{
  "packId": "astronomy-and-space",
  "packName": "Astronomy & Space",
  "packVersion": "0.3.3",
  "shortName": "Astronomy",
  "description": "From why stars twinkle to why Pluto was reclassified: the Sun, the planets, comets, the Milky Way and the tools astronomers use to measure it all.",
  "icon": "🔭",
  "language": "en",
  "lessons": [
    {
      "id": "l01",
      "title": "What You Are Actually Looking At",
      "order": 1,
      "studyGuidePath": "/packs/astronomy-and-space/guides/l01.md",
      "parts": [
        {
          "id": "l01p1",
          "title": "Points and Discs",
          "order": 1,
          "studyGuideAnchor": "points-and-discs",
          "itemIds": [
            "ast-f-twinkle-is-our-air",
            "ast-f-planet-disc-averages-out",
            "ast-f-planet-still-a-dot",
            "ast-f-low-planet-can-twinkle",
            "ast-d-airmass",
            "ast-p-proxima-centauri-distance",
            "ast-p-r-doradus-disc",
            "ast-q-why-stars-twinkle",
            "ast-q-star-through-telescope",
            "czr-ast-d-airmass",
            "tfr-ast-d-airmass"
          ]
        },
        {
          "id": "l01p2",
          "title": "Things That Move",
          "order": 2,
          "studyGuideAnchor": "things-that-move",
          "itemIds": [
            "ast-f-iss-is-a-mirror",
            "ast-f-iss-speed-and-altitude",
            "ast-f-meteor-lasts-seconds",
            "ast-f-orbit-is-crowded",
            "ast-d-fireball",
            "ast-p-aircraft-position-lights",
            "ast-p-satellite-pass-length",
            "ast-q-iss-fades-mid-sky",
            "ast-q-satellite-signature",
            "czr-ast-d-fireball",
            "tfr-ast-d-fireball"
          ]
        },
        {
          "id": "l01p3",
          "title": "How Bright Is Bright",
          "order": 3,
          "studyGuideAnchor": "how-bright-is-bright",
          "itemIds": [
            "ast-f-magnitude-runs-backwards",
            "ast-f-five-magnitudes-hundredfold",
            "ast-f-only-2500-stars",
            "ast-f-ecliptic-and-daily-drift",
            "ast-d-apparent-magnitude",
            "ast-q-magnitude-faintest-object",
            "ast-n-magnitude-sun",
            "ast-n-magnitude-full-moon",
            "ast-n-magnitude-venus-brightest",
            "ast-n-magnitude-sirius",
            "ast-n-magnitude-vega",
            "ast-n-magnitude-naked-eye-limit",
            "czr-ast-d-apparent-magnitude"
          ]
        }
      ],
      "objectives": [
        {
          "id": "o1",
          "statement": "Tell a planet, a star, a satellite and the ISS apart, and say what each difference reveals",
          "demonstrationIds": [
            "d-l01p1",
            "d-l01p2",
            "d-l01p3"
          ]
        }
      ],
      "demonstrations": [
        {
          "id": "d-l01p1",
          "label": "Points and Discs",
          "itemIds": [
            "ast-d-airmass",
            "ast-p-proxima-centauri-distance",
            "ast-p-r-doradus-disc",
            "ast-q-why-stars-twinkle",
            "ast-q-star-through-telescope",
            "czr-ast-d-airmass",
            "tfr-ast-d-airmass"
          ],
          "requiredCorrect": 5
        },
        {
          "id": "d-l01p2",
          "label": "Things That Move",
          "itemIds": [
            "ast-d-fireball",
            "ast-p-aircraft-position-lights",
            "ast-p-satellite-pass-length",
            "ast-q-iss-fades-mid-sky",
            "ast-q-satellite-signature",
            "czr-ast-d-fireball",
            "tfr-ast-d-fireball"
          ],
          "requiredCorrect": 5
        },
        {
          "id": "d-l01p3",
          "label": "How Bright Is Bright",
          "itemIds": [
            "ast-d-apparent-magnitude",
            "ast-q-magnitude-faintest-object",
            "ast-n-magnitude-sun",
            "ast-n-magnitude-full-moon",
            "ast-n-magnitude-venus-brightest",
            "ast-n-magnitude-sirius",
            "ast-n-magnitude-vega",
            "ast-n-magnitude-naked-eye-limit",
            "czr-ast-d-apparent-magnitude"
          ],
          "requiredCorrect": 6
        }
      ],
      "objectiveTests": [
        {
          "id": "ot-l01",
          "objectiveId": "o1",
          "title": "What You Are Actually Looking At — check",
          "mcqIds": [
            "ast-q-why-stars-twinkle",
            "ast-q-star-through-telescope",
            "ast-q-iss-fades-mid-sky",
            "ast-q-satellite-signature",
            "ast-q-magnitude-faintest-object"
          ]
        }
      ]
    },
    {
      "id": "l02",
      "title": "The Earth, Moon and Sun",
      "order": 2,
      "studyGuidePath": "/packs/astronomy-and-space/guides/l02.md",
      "parts": [
        {
          "id": "l02p1",
          "title": "Why the Moon Has Phases",
          "order": 1,
          "studyGuideAnchor": "why-the-moon-has-phases",
          "itemIds": [
            "ast-f-moon-half-lit",
            "ast-f-moon-two-months",
            "ast-f-moon-far-side",
            "ast-f-moon-tilt-nodes",
            "ast-d-synodic-month",
            "ast-p-moon-tidal-lock",
            "ast-p-moon-perigee",
            "ast-q-moon-first-quarter",
            "ast-q-moon-phase-cause",
            "czr-ast-d-synodic-month",
            "tfr-ast-d-synodic-month"
          ]
        },
        {
          "id": "l02p2",
          "title": "Why Eclipses Are Rare",
          "order": 2,
          "studyGuideAnchor": "why-eclipses-are-rare",
          "itemIds": [
            "ast-f-eclipse-umbra-strip",
            "ast-f-eclipse-totality-brief",
            "ast-f-eclipse-400-coincidence",
            "ast-f-eclipse-saros-cycle",
            "ast-d-penumbra",
            "ast-p-annular-eclipse",
            "ast-p-iso-solar-filter",
            "ast-q-eclipse-solar-phase",
            "ast-q-eclipse-optics-filter",
            "czr-ast-d-penumbra",
            "tfr-ast-d-penumbra"
          ]
        },
        {
          "id": "l02p3",
          "title": "Seasons and Tides",
          "order": 3,
          "studyGuideAnchor": "seasons-and-tides",
          "itemIds": [
            "ast-f-earth-tilt-seasons",
            "ast-f-summer-at-aphelion",
            "ast-f-tides-two-bulges",
            "ast-f-moon-retreat-laser",
            "ast-d-equinox",
            "ast-p-spring-tide",
            "ast-p-solar-retinopathy",
            "ast-q-seasons-cause",
            "ast-q-tides-distance-cube",
            "czr-ast-d-equinox",
            "tfr-ast-d-equinox"
          ]
        }
      ],
      "objectives": [
        {
          "id": "o2",
          "statement": "Explain phases, eclipses, seasons and tides from the geometry of two orbits",
          "demonstrationIds": [
            "d-l02p1",
            "d-l02p2",
            "d-l02p3"
          ]
        }
      ],
      "demonstrations": [
        {
          "id": "d-l02p1",
          "label": "Why the Moon Has Phases",
          "itemIds": [
            "ast-d-synodic-month",
            "ast-p-moon-tidal-lock",
            "ast-p-moon-perigee",
            "ast-q-moon-first-quarter",
            "ast-q-moon-phase-cause",
            "czr-ast-d-synodic-month",
            "tfr-ast-d-synodic-month"
          ],
          "requiredCorrect": 5
        },
        {
          "id": "d-l02p2",
          "label": "Why Eclipses Are Rare",
          "itemIds": [
            "ast-d-penumbra",
            "ast-p-annular-eclipse",
            "ast-p-iso-solar-filter",
            "ast-q-eclipse-solar-phase",
            "ast-q-eclipse-optics-filter",
            "czr-ast-d-penumbra",
            "tfr-ast-d-penumbra"
          ],
          "requiredCorrect": 5
        },
        {
          "id": "d-l02p3",
          "label": "Seasons and Tides",
          "itemIds": [
            "ast-d-equinox",
            "ast-p-spring-tide",
            "ast-p-solar-retinopathy",
            "ast-q-seasons-cause",
            "ast-q-tides-distance-cube",
            "czr-ast-d-equinox",
            "tfr-ast-d-equinox"
          ],
          "requiredCorrect": 5
        }
      ],
      "objectiveTests": [
        {
          "id": "ot-l02",
          "objectiveId": "o2",
          "title": "The Earth, Moon and Sun — check",
          "mcqIds": [
            "ast-q-moon-first-quarter",
            "ast-q-moon-phase-cause",
            "ast-q-eclipse-solar-phase",
            "ast-q-eclipse-optics-filter",
            "ast-q-seasons-cause",
            "ast-q-tides-distance-cube"
          ]
        }
      ]
    },
    {
      "id": "l03",
      "title": "The Sun",
      "order": 3,
      "studyGuidePath": "/packs/astronomy-and-space/guides/l03.md",
      "parts": [
        {
          "id": "l03p1",
          "title": "Inside the Sun",
          "order": 1,
          "studyGuideAnchor": "inside-the-sun",
          "itemIds": [
            "ast-f-sun-not-a-fire",
            "ast-f-sun-ten-jupiters",
            "ast-f-sun-pp-chain",
            "ast-f-sun-fusion-in-core",
            "ast-f-sun-half-done",
            "ast-p-sun-spectral-class",
            "ast-p-sun-composition",
            "ast-d-solar-mass",
            "ast-q-sun-holds-itself-up",
            "ast-q-sun-cno-share",
            "tfr-ast-d-solar-mass"
          ]
        },
        {
          "id": "l03p2",
          "title": "The Sun's Weather",
          "order": 2,
          "studyGuideAnchor": "the-sun-s-weather",
          "itemIds": [
            "ast-f-sun-slow-escape",
            "ast-f-sun-granulation",
            "ast-f-sun-temperature-inversion",
            "ast-f-coronal-heating-suspects",
            "ast-f-maunder-minimum",
            "ast-p-differential-rotation",
            "ast-p-sunspot-cycle-length",
            "ast-d-solar-flare",
            "ast-q-sunspot-looks-dark",
            "ast-q-flare-class-steps",
            "czr-ast-d-solar-flare",
            "tfr-ast-d-solar-flare"
          ]
        },
        {
          "id": "l03p3",
          "title": "Reach and Consequence",
          "order": 3,
          "studyGuideAnchor": "reach-and-consequence",
          "itemIds": [
            "ast-f-solar-wind-fills-space",
            "ast-f-aurora-own-light",
            "ast-f-carrington-event-1859",
            "ast-f-parker-inside-corona",
            "ast-p-cme-travel-time",
            "ast-p-g5-storm-grade",
            "ast-d-coronal-hole",
            "ast-q-solar-viewing-safety",
            "ast-q-storm-hazard-target",
            "czr-ast-d-coronal-hole",
            "tfr-ast-d-coronal-hole"
          ]
        }
      ],
      "objectives": [
        {
          "id": "o3",
          "statement": "Describe the Sun's structure and how its energy and weather reach Earth",
          "demonstrationIds": [
            "d-l03p1",
            "d-l03p2",
            "d-l03p3"
          ]
        }
      ],
      "demonstrations": [
        {
          "id": "d-l03p1",
          "label": "Inside the Sun",
          "itemIds": [
            "ast-p-sun-spectral-class",
            "ast-p-sun-composition",
            "ast-d-solar-mass",
            "ast-q-sun-holds-itself-up",
            "ast-q-sun-cno-share",
            "tfr-ast-d-solar-mass"
          ],
          "requiredCorrect": 4
        },
        {
          "id": "d-l03p2",
          "label": "The Sun's Weather",
          "itemIds": [
            "ast-p-differential-rotation",
            "ast-p-sunspot-cycle-length",
            "ast-d-solar-flare",
            "ast-q-sunspot-looks-dark",
            "ast-q-flare-class-steps",
            "czr-ast-d-solar-flare",
            "tfr-ast-d-solar-flare"
          ],
          "requiredCorrect": 5
        },
        {
          "id": "d-l03p3",
          "label": "Reach and Consequence",
          "itemIds": [
            "ast-p-cme-travel-time",
            "ast-p-g5-storm-grade",
            "ast-d-coronal-hole",
            "ast-q-solar-viewing-safety",
            "ast-q-storm-hazard-target",
            "czr-ast-d-coronal-hole",
            "tfr-ast-d-coronal-hole"
          ],
          "requiredCorrect": 5
        }
      ],
      "objectiveTests": [
        {
          "id": "ot-l03",
          "objectiveId": "o3",
          "title": "The Sun — check",
          "mcqIds": [
            "ast-q-sun-holds-itself-up",
            "ast-q-sun-cno-share",
            "ast-q-sunspot-looks-dark",
            "ast-q-flare-class-steps",
            "ast-q-solar-viewing-safety",
            "ast-q-storm-hazard-target"
          ]
        }
      ]
    },
    {
      "id": "l04",
      "title": "Mercury and Venus",
      "order": 4,
      "studyGuidePath": "/packs/astronomy-and-space/guides/l04.md",
      "parts": [
        {
          "id": "l04p1",
          "title": "Mercury, the Extreme Small World",
          "order": 1,
          "studyGuideAnchor": "mercury-the-extreme-small-world",
          "itemIds": [
            "ast-f-mercury-long-day",
            "ast-f-mercury-polar-ice",
            "ast-f-mercury-metal-core",
            "ast-f-mercury-temp-swing",
            "ast-d-exosphere",
            "ast-p-caloris-basin",
            "ast-p-mercury-year",
            "ast-q-mercury-night-cold",
            "ast-q-mercury-core-share",
            "ast-q-mercury-gravity-twin",
            "czr-ast-d-exosphere",
            "tfr-ast-d-exosphere"
          ]
        },
        {
          "id": "l04p2",
          "title": "Venus, the Runaway",
          "order": 2,
          "studyGuideAnchor": "venus-the-runaway",
          "itemIds": [
            "ast-f-venus-backward-spin",
            "ast-f-venus-lead-melting-surface",
            "ast-f-venus-acid-cloud-deck",
            "ast-f-venus-radar-mapping",
            "ast-p-venus-co2-inventory",
            "ast-p-venus-surface-age",
            "ast-d-retrograde",
            "ast-q-venus-brightest-planet",
            "ast-q-venera-lander-survival",
            "ast-q-venus-dominant-gas",
            "czr-ast-d-retrograde",
            "tfr-ast-d-retrograde"
          ]
        },
        {
          "id": "l04p3",
          "title": "Why Neither Kept Water",
          "order": 3,
          "studyGuideAnchor": "why-neither-kept-water",
          "itemIds": [
            "ast-f-escape-velocity-ladder",
            "ast-f-mercury-never-held-air",
            "ast-f-venus-water-left-first",
            "ast-f-magnetic-field-no-shield",
            "ast-p-venus-early-ocean-model",
            "ast-p-planets-without-moons",
            "ast-d-runaway-greenhouse",
            "ast-q-venus-collapse-order",
            "ast-q-atmosphere-retention-levers",
            "ast-q-lowest-escape-speed",
            "tfr-ast-d-runaway-greenhouse"
          ]
        }
      ],
      "objectives": [
        {
          "id": "o4",
          "statement": "Contrast Mercury and Venus, and say why neither kept liquid water",
          "demonstrationIds": [
            "d-l04p1",
            "d-l04p2",
            "d-l04p3"
          ]
        }
      ],
      "demonstrations": [
        {
          "id": "d-l04p1",
          "label": "Mercury, the Extreme Small World",
          "itemIds": [
            "ast-d-exosphere",
            "ast-p-caloris-basin",
            "ast-p-mercury-year",
            "ast-q-mercury-night-cold",
            "ast-q-mercury-core-share",
            "ast-q-mercury-gravity-twin",
            "czr-ast-d-exosphere",
            "tfr-ast-d-exosphere"
          ],
          "requiredCorrect": 5
        },
        {
          "id": "d-l04p2",
          "label": "Venus, the Runaway",
          "itemIds": [
            "ast-p-venus-co2-inventory",
            "ast-p-venus-surface-age",
            "ast-d-retrograde",
            "ast-q-venus-brightest-planet",
            "ast-q-venera-lander-survival",
            "ast-q-venus-dominant-gas",
            "czr-ast-d-retrograde",
            "tfr-ast-d-retrograde"
          ],
          "requiredCorrect": 5
        },
        {
          "id": "d-l04p3",
          "label": "Why Neither Kept Water",
          "itemIds": [
            "ast-p-venus-early-ocean-model",
            "ast-p-planets-without-moons",
            "ast-d-runaway-greenhouse",
            "ast-q-venus-collapse-order",
            "ast-q-atmosphere-retention-levers",
            "ast-q-lowest-escape-speed",
            "tfr-ast-d-runaway-greenhouse"
          ],
          "requiredCorrect": 5
        }
      ],
      "objectiveTests": [
        {
          "id": "ot-l04",
          "objectiveId": "o4",
          "title": "Mercury and Venus — check",
          "mcqIds": [
            "ast-q-mercury-night-cold",
            "ast-q-mercury-core-share",
            "ast-q-mercury-gravity-twin",
            "ast-q-venus-brightest-planet",
            "ast-q-venera-lander-survival",
            "ast-q-venus-dominant-gas",
            "ast-q-venus-collapse-order",
            "ast-q-atmosphere-retention-levers",
            "ast-q-lowest-escape-speed"
          ]
        }
      ]
    },
    {
      "id": "l05",
      "title": "Earth and Mars",
      "order": 5,
      "studyGuidePath": "/packs/astronomy-and-space/guides/l05.md",
      "parts": [
        {
          "id": "l05p1",
          "title": "Earth as a Planet",
          "order": 1,
          "studyGuideAnchor": "earth-as-a-planet",
          "itemIds": [
            "ast-f-earth-moving-plates",
            "ast-f-earth-oxygen-from-life",
            "ast-f-earth-carbon-thermostat",
            "ast-f-earth-oversized-moon",
            "ast-p-earth-sidereal-day",
            "ast-p-earth-global-ocean",
            "ast-d-lithosphere",
            "ast-q-earth-oxygen-source",
            "ast-q-earth-plate-tectonics",
            "ast-q-earth-carbon-weathering",
            "czr-ast-d-lithosphere",
            "tfr-ast-d-lithosphere"
          ]
        },
        {
          "id": "l05p2",
          "title": "Mars, the World That Dried Out",
          "order": 2,
          "studyGuideAnchor": "mars-the-world-that-dried-out",
          "itemIds": [
            "ast-f-mars-sol-clock",
            "ast-f-mars-olympus-mons",
            "ast-f-mars-valles-marineris",
            "ast-f-mars-water-evidence",
            "ast-f-mars-temperature-range",
            "ast-p-phobos-moon",
            "ast-p-deimos-moon",
            "ast-d-sol-martian-day",
            "ast-q-mars-olympus-growth",
            "ast-q-mars-year-length",
            "czr-ast-d-sol-martian-day",
            "tfr-ast-d-sol-martian-day"
          ]
        },
        {
          "id": "l05p3",
          "title": "What Made the Difference",
          "order": 3,
          "studyGuideAnchor": "what-made-the-difference",
          "itemIds": [
            "ast-f-mars-tenth-of-mass",
            "ast-f-mars-same-gas-as-venus",
            "ast-f-mars-maven-loss-rate",
            "ast-f-earth-magnetosphere-field",
            "ast-f-mars-polar-dry-ice",
            "ast-p-sputtering-loss",
            "ast-p-earth-carbon-in-rock",
            "ast-d-escape-speed",
            "ast-q-mars-argon-accounting",
            "ast-q-mars-escape-energy",
            "ast-q-atmosphere-light-gases-first",
            "tfr-ast-d-escape-speed"
          ]
        }
      ],
      "objectives": [
        {
          "id": "o5",
          "statement": "Compare Earth and Mars, and explain why only one stayed habitable",
          "demonstrationIds": [
            "d-l05p1",
            "d-l05p2",
            "d-l05p3"
          ]
        }
      ],
      "demonstrations": [
        {
          "id": "d-l05p1",
          "label": "Earth as a Planet",
          "itemIds": [
            "ast-p-earth-sidereal-day",
            "ast-p-earth-global-ocean",
            "ast-d-lithosphere",
            "ast-q-earth-oxygen-source",
            "ast-q-earth-plate-tectonics",
            "ast-q-earth-carbon-weathering",
            "czr-ast-d-lithosphere",
            "tfr-ast-d-lithosphere"
          ],
          "requiredCorrect": 5
        },
        {
          "id": "d-l05p2",
          "label": "Mars, the World That Dried Out",
          "itemIds": [
            "ast-p-phobos-moon",
            "ast-p-deimos-moon",
            "ast-d-sol-martian-day",
            "ast-q-mars-olympus-growth",
            "ast-q-mars-year-length",
            "czr-ast-d-sol-martian-day",
            "tfr-ast-d-sol-martian-day"
          ],
          "requiredCorrect": 5
        },
        {
          "id": "d-l05p3",
          "label": "What Made the Difference",
          "itemIds": [
            "ast-p-sputtering-loss",
            "ast-p-earth-carbon-in-rock",
            "ast-d-escape-speed",
            "ast-q-mars-argon-accounting",
            "ast-q-mars-escape-energy",
            "ast-q-atmosphere-light-gases-first",
            "tfr-ast-d-escape-speed"
          ],
          "requiredCorrect": 5
        }
      ],
      "objectiveTests": [
        {
          "id": "ot-l05",
          "objectiveId": "o5",
          "title": "Earth and Mars — check",
          "mcqIds": [
            "ast-q-earth-oxygen-source",
            "ast-q-earth-plate-tectonics",
            "ast-q-earth-carbon-weathering",
            "ast-q-mars-olympus-growth",
            "ast-q-mars-year-length",
            "ast-q-mars-argon-accounting",
            "ast-q-mars-escape-energy",
            "ast-q-atmosphere-light-gases-first"
          ]
        }
      ]
    },
    {
      "id": "l06",
      "title": "Jupiter",
      "order": 6,
      "studyGuidePath": "/packs/astronomy-and-space/guides/l06.md",
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        {
          "id": "l06p1",
          "title": "The Giant Itself",
          "order": 1,
          "studyGuideAnchor": "the-giant-itself",
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            "ast-f-jupiter-no-surface",
            "ast-f-jupiter-star-ingredients",
            "ast-f-jupiter-shoemaker-levy",
            "ast-d-metallic-hydrogen",
            "ast-p-jupiter-day-length",
            "ast-p-jupiter-year-length",
            "ast-q-jupiter-fusion-threshold",
            "ast-q-jupiter-cloud-gravity"
          ]
        },
        {
          "id": "l06p2",
          "title": "Storms and Magnetism",
          "order": 2,
          "studyGuideAnchor": "storms-and-magnetism",
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            "ast-f-jupiter-red-spot",
            "ast-f-jupiter-oblate",
            "ast-f-jupiter-belts-zones",
            "ast-f-jupiter-field-no-iron",
            "ast-f-jupiter-rings-moon-count",
            "ast-d-radiation-belt",
            "ast-p-jupiter-magnetosphere",
            "ast-p-juno-polar-orbit",
            "ast-q-jupiter-belt-fuel",
            "ast-q-jupiter-dynamo-source",
            "czr-ast-d-radiation-belt"
          ]
        },
        {
          "id": "l06p3",
          "title": "The Galilean Moons",
          "order": 3,
          "studyGuideAnchor": "the-galilean-moons",
          "itemIds": [
            "ast-f-galileo-four-points",
            "ast-f-galilean-resonance",
            "ast-f-io-four-hundred-volcanoes",
            "ast-d-tidal-heating",
            "ast-p-europa-ice-shell",
            "ast-q-callisto-cratering",
            "ast-c-io-moon",
            "ast-c-europa-moon",
            "ast-c-ganymede-moon",
            "ast-c-callisto-moon",
            "ast-c-europa-clipper-mission",
            "ast-c-sidereus-nuncius",
            "tfr-ast-d-tidal-heating"
          ]
        }
      ],
      "objectives": [
        {
          "id": "o6",
          "statement": "Characterise Jupiter and its major moons",
          "demonstrationIds": [
            "d-l06p1",
            "d-l06p2",
            "d-l06p3"
          ]
        }
      ],
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        {
          "id": "d-l06p1",
          "label": "The Giant Itself",
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            "ast-d-metallic-hydrogen",
            "ast-p-jupiter-day-length",
            "ast-p-jupiter-year-length",
            "ast-q-jupiter-fusion-threshold",
            "ast-q-jupiter-cloud-gravity"
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          "requiredCorrect": 3
        },
        {
          "id": "d-l06p2",
          "label": "Storms and Magnetism",
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            "ast-p-juno-polar-orbit",
            "ast-q-jupiter-belt-fuel",
            "ast-q-jupiter-dynamo-source",
            "czr-ast-d-radiation-belt"
          ],
          "requiredCorrect": 4
        },
        {
          "id": "d-l06p3",
          "label": "The Galilean Moons",
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            "ast-d-tidal-heating",
            "ast-p-europa-ice-shell",
            "ast-q-callisto-cratering",
            "ast-c-io-moon",
            "ast-c-europa-moon",
            "ast-c-ganymede-moon",
            "ast-c-callisto-moon",
            "ast-c-europa-clipper-mission",
            "ast-c-sidereus-nuncius",
            "tfr-ast-d-tidal-heating"
          ],
          "requiredCorrect": 6
        }
      ],
      "objectiveTests": [
        {
          "id": "ot-l06",
          "objectiveId": "o6",
          "title": "Jupiter — check",
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            "ast-q-jupiter-fusion-threshold",
            "ast-q-jupiter-cloud-gravity",
            "ast-q-jupiter-belt-fuel",
            "ast-q-jupiter-dynamo-source",
            "ast-q-callisto-cratering"
          ]
        }
      ]
    },
    {
      "id": "l07",
      "title": "Saturn",
      "order": 7,
      "studyGuidePath": "/packs/astronomy-and-space/guides/l07.md",
      "parts": [
        {
          "id": "l07p1",
          "title": "The Planet That Would Float",
          "order": 1,
          "studyGuideAnchor": "the-planet-that-would-float",
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            "ast-f-saturn-lighter-than-water",
            "ast-f-saturn-no-surface",
            "ast-f-saturn-hexagon",
            "ast-f-saturn-ring-clock",
            "ast-d-oblateness",
            "ast-p-saturn-from-the-sun",
            "ast-p-saturn-axial-tilt",
            "ast-q-saturn-day-not-year",
            "ast-q-saturn-ringed-worlds",
            "czr-ast-d-oblateness",
            "tfr-ast-d-oblateness"
          ]
        },
        {
          "id": "l07p2",
          "title": "The Rings",
          "order": 2,
          "studyGuideAnchor": "the-rings",
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            "ast-f-saturn-rings-are-ice",
            "ast-f-saturn-rings-thickness",
            "ast-f-saturn-rings-lettering",
            "ast-f-saturn-ring-age-argument",
            "ast-d-roche-limit",
            "ast-p-cassini-grand-finale",
            "ast-p-saturn-ring-rain",
            "ast-q-encke-gap-held-open",
            "ast-q-saturn-rings-composition",
            "czr-ast-d-roche-limit",
            "tfr-ast-d-roche-limit"
          ]
        },
        {
          "id": "l07p3",
          "title": "The Moons of Saturn",
          "order": 3,
          "studyGuideAnchor": "the-moons-of-saturn",
          "itemIds": [
            "ast-f-saturn-moon-count-dated",
            "ast-f-saturn-moon-size-ladder",
            "ast-f-saturn-moons-found-from-earth",
            "ast-f-cassini-deliberate-ending",
            "ast-d-tiger-stripes",
            "ast-c-moon-titan",
            "ast-c-moon-enceladus",
            "ast-c-moon-mimas",
            "ast-c-moon-tethys",
            "ast-c-moon-dione",
            "ast-c-moon-rhea",
            "ast-c-moon-iapetus",
            "ast-c-moon-phoebe",
            "ast-c-moon-hyperion",
            "ast-q-titan-standing-seas",
            "ast-q-enceladus-silica-grains",
            "tfr-ast-d-tiger-stripes",
            "ot-cov-o7-1",
            "ot-cov-o7-2",
            "ot-cov-o7-3",
            "ot-cov-o7-4"
          ]
        }
      ],
      "objectives": [
        {
          "id": "o7",
          "statement": "Characterise Saturn, explain its rings, and place Titan and Enceladus",
          "demonstrationIds": [
            "d-l07p1",
            "d-l07p2",
            "d-l07p3"
          ]
        }
      ],
      "demonstrations": [
        {
          "id": "d-l07p1",
          "label": "The Planet That Would Float",
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            "ast-d-oblateness",
            "ast-p-saturn-from-the-sun",
            "ast-p-saturn-axial-tilt",
            "ast-q-saturn-day-not-year",
            "ast-q-saturn-ringed-worlds",
            "czr-ast-d-oblateness",
            "tfr-ast-d-oblateness",
            "ot-cov-o7-1",
            "ot-cov-o7-2",
            "ot-cov-o7-3",
            "ot-cov-o7-4"
          ],
          "requiredCorrect": 5
        },
        {
          "id": "d-l07p2",
          "label": "The Rings",
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            "ast-d-roche-limit",
            "ast-p-cassini-grand-finale",
            "ast-p-saturn-ring-rain",
            "ast-q-encke-gap-held-open",
            "ast-q-saturn-rings-composition",
            "czr-ast-d-roche-limit",
            "tfr-ast-d-roche-limit"
          ],
          "requiredCorrect": 5
        },
        {
          "id": "d-l07p3",
          "label": "The Moons of Saturn",
          "itemIds": [
            "ast-d-tiger-stripes",
            "ast-c-moon-titan",
            "ast-c-moon-enceladus",
            "ast-c-moon-mimas",
            "ast-c-moon-tethys",
            "ast-c-moon-dione",
            "ast-c-moon-rhea",
            "ast-c-moon-iapetus",
            "ast-c-moon-phoebe",
            "ast-c-moon-hyperion",
            "ast-q-titan-standing-seas",
            "ast-q-enceladus-silica-grains",
            "tfr-ast-d-tiger-stripes"
          ],
          "requiredCorrect": 8
        }
      ],
      "objectiveTests": [
        {
          "id": "ot-l07",
          "objectiveId": "o7",
          "title": "Saturn — check",
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            "ast-q-saturn-day-not-year",
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            "ast-q-saturn-rings-composition",
            "ast-q-titan-standing-seas",
            "ast-q-enceladus-silica-grains",
            "ot-cov-o7-1",
            "ot-cov-o7-2",
            "ot-cov-o7-3",
            "ot-cov-o7-4"
          ]
        }
      ]
    },
    {
      "id": "l08",
      "title": "Uranus and Neptune",
      "order": 8,
      "studyGuidePath": "/packs/astronomy-and-space/guides/l08.md",
      "parts": [
        {
          "id": "l08p1",
          "title": "Why Ice Giant Is a Real Category",
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          "studyGuideAnchor": "why-ice-giant-is-a-real-category",
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            "ast-f-ice-giant-not-frozen",
            "ast-f-icegiant-four-earths-wide",
            "ast-f-neptune-smaller-heavier",
            "ast-f-neptune-one-orbit-since-discovery",
            "ast-p-uranus-day-length",
            "ast-d-ice-giant",
            "ast-q-icegiant-interior",
            "ast-q-neptune-mass-flip"
          ]
        },
        {
          "id": "l08p2",
          "title": "The Tipped World",
          "order": 2,
          "studyGuideAnchor": "the-tipped-world",
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            "ast-f-uranus-rolls-like-barrel",
            "ast-f-uranus-tilt-hypothesis",
            "ast-f-icegiant-methane-haze",
            "ast-f-neptune-great-dark-spot",
            "ast-p-uranus-literary-moons",
            "ast-d-coronae-miranda",
            "ast-q-uranus-hottest-region",
            "ast-q-fastest-winds-planet",
            "czr-ast-d-coronae-miranda",
            "tfr-ast-d-coronae-miranda"
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        },
        {
          "id": "l08p3",
          "title": "Neptune, Found With Mathematics",
          "order": 3,
          "studyGuideAnchor": "neptune-found-with-mathematics",
          "itemIds": [
            "ast-f-neptune-found-on-paper",
            "ast-f-uranus-rings-occultation",
            "ast-f-triton-cold-is-not-dead",
            "ast-p-neptune-ring-names",
            "ast-p-neptune-moon-names",
            "ast-d-occultation",
            "ast-q-neptune-discovery-method",
            "ast-q-icegiant-only-visitor",
            "czr-ast-d-occultation",
            "tfr-ast-d-occultation"
          ]
        }
      ],
      "objectives": [
        {
          "id": "o8",
          "statement": "Distinguish the ice giants from the gas giants, and say why Uranus is tipped over",
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            "d-l08p1",
            "d-l08p2",
            "d-l08p3"
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        }
      ],
      "demonstrations": [
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          "id": "d-l08p1",
          "label": "Why Ice Giant Is a Real Category",
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            "ast-p-uranus-day-length",
            "ast-d-ice-giant",
            "ast-q-icegiant-interior",
            "ast-q-neptune-mass-flip"
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          "requiredCorrect": 3
        },
        {
          "id": "d-l08p2",
          "label": "The Tipped World",
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            "ast-p-uranus-literary-moons",
            "ast-d-coronae-miranda",
            "ast-q-uranus-hottest-region",
            "ast-q-fastest-winds-planet",
            "czr-ast-d-coronae-miranda",
            "tfr-ast-d-coronae-miranda"
          ],
          "requiredCorrect": 4
        },
        {
          "id": "d-l08p3",
          "label": "Neptune, Found With Mathematics",
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            "ast-p-neptune-ring-names",
            "ast-p-neptune-moon-names",
            "ast-d-occultation",
            "ast-q-neptune-discovery-method",
            "ast-q-icegiant-only-visitor",
            "czr-ast-d-occultation",
            "tfr-ast-d-occultation"
          ],
          "requiredCorrect": 5
        }
      ],
      "objectiveTests": [
        {
          "id": "ot-l08",
          "objectiveId": "o8",
          "title": "Uranus and Neptune — check",
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            "ast-q-icegiant-interior",
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            "ast-q-uranus-hottest-region",
            "ast-q-fastest-winds-planet",
            "ast-q-neptune-discovery-method",
            "ast-q-icegiant-only-visitor"
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        }
      ]
    },
    {
      "id": "l09",
      "title": "Asteroids, Meteors and Dwarf Planets",
      "order": 9,
      "studyGuidePath": "/packs/astronomy-and-space/guides/l09.md",
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          "id": "l09p1",
          "title": "The Asteroid Belt",
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          "studyGuideAnchor": "the-asteroid-belt",
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            "ast-f-belt-unfinished-planet",
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            "ast-f-vesta-differentiated",
            "ast-f-jupiter-trojan-swarms",
            "ast-p-asteroid-belt-distance",
            "ast-p-pallas-inclination",
            "ast-d-differentiated",
            "ast-q-belt-no-planet",
            "ast-q-asteroid-c-type-share",
            "czr-ast-d-differentiated",
            "tfr-ast-d-differentiated"
          ]
        },
        {
          "id": "l09p2",
          "title": "Meteoroid, Meteor, Meteorite",
          "order": 2,
          "studyGuideAnchor": "meteoroid-meteor-meteorite",
          "itemIds": [
            "ast-f-meteor-three-words",
            "ast-f-meteoritic-dust-daily",
            "ast-f-meteor-shower-radiant",
            "ast-f-meteorite-falls-finds",
            "ast-p-leonids-tempel-tuttle",
            "ast-p-chondrite-never-melted",
            "ast-d-rock-comet",
            "ast-q-meteor-is-light",
            "ast-q-geminids-parent-body",
            "czr-ast-d-rock-comet",
            "tfr-ast-d-rock-comet"
          ]
        },
        {
          "id": "l09p3",
          "title": "Dwarf Planets and the 2006 Vote",
          "order": 3,
          "studyGuideAnchor": "dwarf-planets-and-the-2006-vote",
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            "ast-f-iau-third-test",
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            "ast-f-pluto-unchanged",
            "ast-f-five-dwarf-planets-list",
            "ast-p-small-solar-system-body",
            "ast-d-dwarf-planet",
            "ast-q-pluto-reclassified-why",
            "ast-p-ceres-dwarf",
            "ast-p-pluto-dwarf",
            "ast-p-haumea-dwarf",
            "ast-p-makemake-dwarf",
            "ast-p-eris-dwarf",
            "tfr-ast-d-dwarf-planet"
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        }
      ],
      "objectives": [
        {
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            "d-l09p1",
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            "d-l09p3"
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        }
      ],
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          "id": "d-l09p1",
          "label": "The Asteroid Belt",
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            "ast-p-asteroid-belt-distance",
            "ast-p-pallas-inclination",
            "ast-d-differentiated",
            "ast-q-belt-no-planet",
            "ast-q-asteroid-c-type-share",
            "czr-ast-d-differentiated",
            "tfr-ast-d-differentiated"
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          "requiredCorrect": 5
        },
        {
          "id": "d-l09p2",
          "label": "Meteoroid, Meteor, Meteorite",
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            "ast-p-leonids-tempel-tuttle",
            "ast-p-chondrite-never-melted",
            "ast-d-rock-comet",
            "ast-q-meteor-is-light",
            "ast-q-geminids-parent-body",
            "czr-ast-d-rock-comet",
            "tfr-ast-d-rock-comet"
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          "requiredCorrect": 5
        },
        {
          "id": "d-l09p3",
          "label": "Dwarf Planets and the 2006 Vote",
          "itemIds": [
            "ast-p-small-solar-system-body",
            "ast-d-dwarf-planet",
            "ast-q-pluto-reclassified-why",
            "ast-p-ceres-dwarf",
            "ast-p-pluto-dwarf",
            "ast-p-haumea-dwarf",
            "ast-p-makemake-dwarf",
            "ast-p-eris-dwarf",
            "tfr-ast-d-dwarf-planet"
          ],
          "requiredCorrect": 6
        }
      ],
      "objectiveTests": [
        {
          "id": "ot-l09",
          "objectiveId": "o9",
          "title": "Asteroids, Meteors and Dwarf Planets — check",
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            "ast-q-belt-no-planet",
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            "ast-q-meteor-is-light",
            "ast-q-geminids-parent-body",
            "ast-q-pluto-reclassified-why"
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        }
      ]
    },
    {
      "id": "l10",
      "title": "The Kuiper Belt, Comets and the Outer Edge",
      "order": 10,
      "studyGuidePath": "/packs/astronomy-and-space/guides/l10.md",
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          "id": "l10p1",
          "title": "The Kuiper Belt",
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            "ast-f-pluto-belt-neighbours",
            "ast-f-arrokoth-contact-binary",
            "ast-p-plutinos-neptune-lock",
            "ast-p-kuiper-belt-mass",
            "ast-d-trans-neptunian-object",
            "ast-q-pluto-neptune-crossing",
            "ast-q-kuiper-belt-catalogue-gap",
            "czr-ast-d-trans-neptunian-object"
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        },
        {
          "id": "l10p2",
          "title": "Comets",
          "order": 2,
          "studyGuideAnchor": "comets",
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            "ast-f-comet-nothing-burns",
            "ast-f-comet-coma-swells",
            "ast-f-comet-two-tails",
            "ast-f-halley-not-a-timetable",
            "ast-f-comet-nucleus-size-brightness",
            "ast-f-67p-rosetta-porous",
            "ast-p-short-period-comets",
            "ast-p-comet-nucleus-town-sized",
            "ast-d-comet-coma",
            "ast-q-comet-tail-direction",
            "ast-q-hale-bopp-brightness",
            "czr-ast-d-comet-coma"
          ]
        },
        {
          "id": "l10p3",
          "title": "Where Does the Solar System End?",
          "order": 3,
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            "ast-f-solar-system-three-edges",
            "ast-f-voyagers-heliopause-crossings",
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            "ast-f-outer-system-light-time",
            "ast-d-heliopause-boundary",
            "ast-q-voyager-still-inside",
            "ast-q-nasa-outer-boundary",
            "ast-n-au-kuiper-belt-edge",
            "ast-n-au-sedna-perihelion",
            "ast-n-au-voyager1-heliopause",
            "ast-n-au-scattered-disc-reach",
            "ast-n-au-oort-inner-near",
            "ast-n-au-oort-inner-far",
            "ast-n-au-oort-outer-edge",
            "tfr-ast-d-heliopause-boundary"
          ]
        }
      ],
      "objectives": [
        {
          "id": "o10",
          "statement": "Place the Kuiper Belt, comets and the Oort Cloud, and order the outer Solar System",
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            "d-l10p1",
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            "d-l10p3"
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        }
      ],
      "demonstrations": [
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          "id": "d-l10p1",
          "label": "The Kuiper Belt",
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            "ast-p-plutinos-neptune-lock",
            "ast-p-kuiper-belt-mass",
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            "ast-q-pluto-neptune-crossing",
            "ast-q-kuiper-belt-catalogue-gap",
            "czr-ast-d-trans-neptunian-object"
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          "requiredCorrect": 4
        },
        {
          "id": "d-l10p2",
          "label": "Comets",
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            "ast-p-short-period-comets",
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            "ast-d-comet-coma",
            "ast-q-comet-tail-direction",
            "ast-q-hale-bopp-brightness",
            "czr-ast-d-comet-coma"
          ],
          "requiredCorrect": 4
        },
        {
          "id": "d-l10p3",
          "label": "Where Does the Solar System End?",
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            "ast-d-heliopause-boundary",
            "ast-q-voyager-still-inside",
            "ast-q-nasa-outer-boundary",
            "ast-n-au-kuiper-belt-edge",
            "ast-n-au-sedna-perihelion",
            "ast-n-au-voyager1-heliopause",
            "ast-n-au-scattered-disc-reach",
            "ast-n-au-oort-inner-near",
            "ast-n-au-oort-inner-far",
            "ast-n-au-oort-outer-edge",
            "tfr-ast-d-heliopause-boundary"
          ],
          "requiredCorrect": 7
        }
      ],
      "objectiveTests": [
        {
          "id": "ot-l10",
          "objectiveId": "o10",
          "title": "The Kuiper Belt, Comets and the Outer Edge — check",
          "mcqIds": [
            "ast-q-pluto-neptune-crossing",
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            "ast-q-comet-tail-direction",
            "ast-q-hale-bopp-brightness",
            "ast-q-voyager-still-inside",
            "ast-q-nasa-outer-boundary"
          ]
        }
      ]
    },
    {
      "id": "l11",
      "title": "How the Solar System Formed",
      "order": 11,
      "studyGuidePath": "/packs/astronomy-and-space/guides/l11.md",
      "parts": [
        {
          "id": "l11p1",
          "title": "From Cloud to Disc",
          "order": 1,
          "studyGuideAnchor": "from-cloud-to-disc",
          "itemIds": [
            "ast-f-solar-system-one-collapse",
            "ast-f-solar-nebula-flat-disc",
            "ast-f-supernova-isotope-clue",
            "ast-f-frost-line-sorted-system",
            "ast-f-sun-holds-99-8-percent",
            "ast-d-frost-line",
            "ast-p-planetesimals-formation",
            "ast-p-belts-unused-material",
            "ast-q-inner-planets-small",
            "ast-q-supernova-trigger-evidence",
            "czr-ast-d-frost-line"
          ]
        },
        {
          "id": "l11p2",
          "title": "Building Planets",
          "order": 2,
          "studyGuideAnchor": "building-planets",
          "itemIds": [
            "ast-f-angular-momentum-problem",
            "ast-f-disc-in-100000-years",
            "ast-f-disc-gas-deadline",
            "ast-f-jupiter-formed-first",
            "ast-f-moon-giant-impact",
            "ast-d-radiometric-dating",
            "ast-p-oldest-dated-solids",
            "ast-q-earth-younger-than-meteorites",
            "ast-q-giant-impact-awkward"
          ]
        },
        {
          "id": "l11p3",
          "title": "Reading the Evidence",
          "order": 3,
          "studyGuideAnchor": "reading-the-evidence",
          "itemIds": [
            "ast-f-late-heavy-bombardment-contested",
            "ast-f-change6-far-side-test",
            "ast-f-51-pegasi-b-discovery",
            "ast-f-metre-sized-barrier",
            "ast-f-frost-line-moves",
            "ast-d-hot-jupiter",
            "ast-p-returned-moon-rock",
            "ast-q-late-heavy-bombardment-status",
            "ast-q-exoplanets-not-default",
            "czr-ast-d-hot-jupiter",
            "tfr-ast-d-hot-jupiter"
          ]
        }
      ],
      "objectives": [
        {
          "id": "o11",
          "statement": "Trace how the Solar System formed and why the frost line sorted it",
          "demonstrationIds": [
            "d-l11p1",
            "d-l11p2",
            "d-l11p3"
          ]
        }
      ],
      "demonstrations": [
        {
          "id": "d-l11p1",
          "label": "From Cloud to Disc",
          "itemIds": [
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            "ast-p-planetesimals-formation",
            "ast-p-belts-unused-material",
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            "ast-q-supernova-trigger-evidence",
            "czr-ast-d-frost-line"
          ],
          "requiredCorrect": 4
        },
        {
          "id": "d-l11p2",
          "label": "Building Planets",
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            "ast-d-radiometric-dating",
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            "ast-q-giant-impact-awkward"
          ],
          "requiredCorrect": 3
        },
        {
          "id": "d-l11p3",
          "label": "Reading the Evidence",
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            "ast-d-hot-jupiter",
            "ast-p-returned-moon-rock",
            "ast-q-late-heavy-bombardment-status",
            "ast-q-exoplanets-not-default",
            "czr-ast-d-hot-jupiter",
            "tfr-ast-d-hot-jupiter"
          ],
          "requiredCorrect": 4
        }
      ],
      "objectiveTests": [
        {
          "id": "ot-l11",
          "objectiveId": "o11",
          "title": "How the Solar System Formed — check",
          "mcqIds": [
            "ast-q-inner-planets-small",
            "ast-q-supernova-trigger-evidence",
            "ast-q-earth-younger-than-meteorites",
            "ast-q-giant-impact-awkward",
            "ast-q-late-heavy-bombardment-status",
            "ast-q-exoplanets-not-default"
          ]
        }
      ]
    },
    {
      "id": "l12",
      "title": "The Lives of Stars",
      "order": 12,
      "studyGuidePath": "/packs/astronomy-and-space/guides/l12.md",
      "parts": [
        {
          "id": "l12p1",
          "title": "How Stars Are Born",
          "order": 1,
          "studyGuideAnchor": "how-stars-are-born",
          "itemIds": [
            "ast-f-molecular-cloud-cold",
            "ast-f-protostar-glows-first",
            "ast-f-fusion-ignition-point",
            "ast-f-cno-twentieth-power",
            "ast-p-giant-molecular-cloud",
            "ast-p-protostar-survival",
            "ast-d-protostar",
            "ast-q-starbirth-gas-temperature",
            "ast-q-protostar-glow-cause",
            "ast-q-cno-temperature-exponent",
            "czr-ast-d-protostar"
          ]
        },
        {
          "id": "l12p2",
          "title": "Mass Decides Everything",
          "order": 2,
          "studyGuideAnchor": "mass-decides-everything",
          "itemIds": [
            "ast-f-spectral-colour-thermometer",
            "ast-f-obafgkm-history",
            "ast-f-mass-luminosity-power",
            "ast-f-massive-stars-die-young",
            "ast-f-sunlike-quiet-ending",
            "ast-p-red-dwarf-share",
            "ast-p-hr-diagram-axes",
            "ast-d-main-sequence",
            "ast-q-tenfold-mass-lifetime",
            "ast-q-core-collapse-birth-mass",
            "ast-n-oclass-hot-end",
            "ast-n-oclass-cool-end",
            "ast-n-gclass-hot-end",
            "ast-n-gclass-cool-end",
            "ast-n-mclass-hot-end",
            "ast-n-mclass-cool-end",
            "tfr-ast-d-main-sequence"
          ]
        },
        {
          "id": "l12p3",
          "title": "How Stars Die",
          "order": 3,
          "studyGuideAnchor": "how-stars-die",
          "itemIds": [
            "ast-f-supernova-light-is-leftover",
            "ast-f-iron-stops-paying",
            "ast-f-three-remnant-endings",
            "ast-f-remnant-limits-approximate",
            "ast-p-tov-limit",
            "ast-d-chandrasekhar-limit",
            "ast-q-sun-black-hole-mass",
            "ast-q-supernova-energy-carrier",
            "ast-q-core-gives-way-iron",
            "ast-c-white-dwarf-remnant",
            "ast-c-neutron-star-remnant",
            "ast-c-black-hole-remnant",
            "ast-c-core-collapse-supernova",
            "ast-c-supernova-neutrinos",
            "ast-c-iron-shell-element",
            "tfr-ast-d-chandrasekhar-limit"
          ]
        }
      ],
      "objectives": [
        {
          "id": "o12",
          "statement": "Classify a star by mass and colour, and predict whether it ends as a dwarf, neutron star or black hole",
          "demonstrationIds": [
            "d-l12p1",
            "d-l12p2",
            "d-l12p3"
          ]
        }
      ],
      "demonstrations": [
        {
          "id": "d-l12p1",
          "label": "How Stars Are Born",
          "itemIds": [
            "ast-p-giant-molecular-cloud",
            "ast-p-protostar-survival",
            "ast-d-protostar",
            "ast-q-starbirth-gas-temperature",
            "ast-q-protostar-glow-cause",
            "ast-q-cno-temperature-exponent",
            "czr-ast-d-protostar"
          ],
          "requiredCorrect": 5
        },
        {
          "id": "d-l12p2",
          "label": "Mass Decides Everything",
          "itemIds": [
            "ast-p-red-dwarf-share",
            "ast-p-hr-diagram-axes",
            "ast-d-main-sequence",
            "ast-q-tenfold-mass-lifetime",
            "ast-q-core-collapse-birth-mass",
            "ast-n-oclass-hot-end",
            "ast-n-oclass-cool-end",
            "ast-n-gclass-hot-end",
            "ast-n-gclass-cool-end",
            "ast-n-mclass-hot-end",
            "ast-n-mclass-cool-end",
            "tfr-ast-d-main-sequence"
          ],
          "requiredCorrect": 8
        },
        {
          "id": "d-l12p3",
          "label": "How Stars Die",
          "itemIds": [
            "ast-p-tov-limit",
            "ast-d-chandrasekhar-limit",
            "ast-q-sun-black-hole-mass",
            "ast-q-supernova-energy-carrier",
            "ast-q-core-gives-way-iron",
            "ast-c-white-dwarf-remnant",
            "ast-c-neutron-star-remnant",
            "ast-c-black-hole-remnant",
            "ast-c-core-collapse-supernova",
            "ast-c-supernova-neutrinos",
            "ast-c-iron-shell-element",
            "tfr-ast-d-chandrasekhar-limit"
          ],
          "requiredCorrect": 8
        }
      ],
      "objectiveTests": [
        {
          "id": "ot-l12",
          "objectiveId": "o12",
          "title": "The Lives of Stars — check",
          "mcqIds": [
            "ast-q-starbirth-gas-temperature",
            "ast-q-protostar-glow-cause",
            "ast-q-cno-temperature-exponent",
            "ast-q-tenfold-mass-lifetime",
            "ast-q-core-collapse-birth-mass",
            "ast-q-sun-black-hole-mass",
            "ast-q-supernova-energy-carrier",
            "ast-q-core-gives-way-iron"
          ]
        }
      ]
    },
    {
      "id": "l13",
      "title": "Galaxies, Distance and Spacetime",
      "order": 13,
      "studyGuidePath": "/packs/astronomy-and-space/guides/l13.md",
      "parts": [
        {
          "id": "l13p1",
          "title": "The Milky Way",
          "order": 1,
          "studyGuideAnchor": "the-milky-way",
          "itemIds": [
            "ast-f-milky-way-thin-disc",
            "ast-f-sun-galactic-orbit",
            "ast-f-milky-way-star-count",
            "ast-f-sagittarius-a-star",
            "ast-p-lenticular-galaxy",
            "ast-p-elliptical-galaxy",
            "ast-d-irregular-galaxy",
            "ast-q-eht-image-content",
            "ast-q-hubble-tuning-fork",
            "tfr-ast-d-irregular-galaxy"
          ]
        },
        {
          "id": "l13p2",
          "title": "Measuring the Universe",
          "order": 2,
          "studyGuideAnchor": "measuring-the-universe",
          "itemIds": [
            "ast-f-light-year-is-distance",
            "ast-f-distance-ladder-rungs",
            "ast-f-andromeda-approaching",
            "ast-f-andromeda-merger-open",
            "ast-p-parallax-rung",
            "ast-d-standard-candle",
            "ast-q-parsec-definition",
            "ast-q-galaxy-merger-stars",
            "ast-n-ly-parsec",
            "ast-n-ly-thin-disc-height",
            "ast-n-ly-sun-to-centre",
            "ast-n-ly-milky-way-width",
            "ast-n-ly-andromeda-distance",
            "ast-n-ly-local-group-span"
          ]
        },
        {
          "id": "l13p3",
          "title": "Gravity, Spacetime and Expansion",
          "order": 3,
          "studyGuideAnchor": "gravity-spacetime-and-expansion",
          "itemIds": [
            "ast-f-spacetime-curvature",
            "ast-f-gravitational-lensing-arcs",
            "ast-f-gps-relativity-correction",
            "ast-f-hubble-tension-gap",
            "ast-p-cosmological-redshift",
            "ast-p-einstein-ring",
            "ast-d-spacetime",
            "ast-q-light-deflection-cause",
            "ast-q-cosmological-redshift-cause"
          ]
        }
      ],
      "objectives": [
        {
          "id": "o13",
          "statement": "Order cosmic distances and explain how gravity and spacetime shape what is there.",
          "demonstrationIds": [
            "d-l13p1",
            "d-l13p2",
            "d-l13p3"
          ]
        }
      ],
      "demonstrations": [
        {
          "id": "d-l13p1",
          "label": "The Milky Way",
          "itemIds": [
            "ast-p-lenticular-galaxy",
            "ast-p-elliptical-galaxy",
            "ast-d-irregular-galaxy",
            "ast-q-eht-image-content",
            "ast-q-hubble-tuning-fork",
            "tfr-ast-d-irregular-galaxy"
          ],
          "requiredCorrect": 4
        },
        {
          "id": "d-l13p2",
          "label": "Measuring the Universe",
          "itemIds": [
            "ast-p-parallax-rung",
            "ast-d-standard-candle",
            "ast-q-parsec-definition",
            "ast-q-galaxy-merger-stars",
            "ast-n-ly-parsec",
            "ast-n-ly-thin-disc-height",
            "ast-n-ly-sun-to-centre",
            "ast-n-ly-milky-way-width",
            "ast-n-ly-andromeda-distance",
            "ast-n-ly-local-group-span"
          ],
          "requiredCorrect": 6
        },
        {
          "id": "d-l13p3",
          "label": "Gravity, Spacetime and Expansion",
          "itemIds": [
            "ast-p-cosmological-redshift",
            "ast-p-einstein-ring",
            "ast-d-spacetime",
            "ast-q-light-deflection-cause",
            "ast-q-cosmological-redshift-cause"
          ],
          "requiredCorrect": 3
        }
      ],
      "objectiveTests": [
        {
          "id": "ot-l13",
          "objectiveId": "o13",
          "title": "Galaxies, Distance and Spacetime — check",
          "mcqIds": [
            "ast-q-eht-image-content",
            "ast-q-hubble-tuning-fork",
            "ast-q-parsec-definition",
            "ast-q-galaxy-merger-stars",
            "ast-q-light-deflection-cause",
            "ast-q-cosmological-redshift-cause"
          ]
        }
      ]
    }
  ],
  "items": [
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      "id": "ast-f-twinkle-is-our-air",
      "shape": "fact",
      "title": "The Flicker Is Our Air",
      "body": "**Scintillation** — twinkling — happens entirely in Earth's atmosphere. A ray of starlight bends slightly each time it crosses between warmer and cooler pockets of air; the pockets keep moving, and the narrow beam wanders in and out of your eye. Seen from space, **nothing twinkles**. The flicker is a measurement of our own air, not of the star.",
      "factVariant": "image-heavy",
      "imageCaption": "Twinkling is the one thing in the night sky that tells you about Earth.",
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "starlight refraction through turbulent atmospheric layers diagram",
        "imagePrompt": "Flat vector schematic: a single ray of starlight enters Earth's atmosphere from above and kinks at each boundary between labelled warm and cool air pockets, reaching an eye on the ground offset from the star's true direction. Light background, labelled layers, no photographic texture.",
        "alt": "Diagram of one ray of starlight bending at each boundary between warmer and cooler air pockets, arriving at an eye on the ground displaced from its true direction",
        "depictable": true,
        "allowGenerated": true
      },
      "source": {
        "label": "University of Wisconsin–Madison — Why do stars appear to twinkle in the night sky?",
        "url": "https://news.wisc.edu/curiosities-why-do-stars-appear-to-twinkle-in-the-night-sky/"
      },
      "tags": [
        "l01p1",
        "twinkling",
        "atmosphere"
      ],
      "uid": "1d56ldbcfohnd"
    },
    {
      "id": "ast-f-planet-disc-averages-out",
      "shape": "fact",
      "title": "Why a Disc Holds Steady",
      "body": "A planet is close enough to be a real **disc**: the naked-eye planets span roughly **10 to 50 arcseconds**, and Jupiter reaches about 49 arcseconds at opposition. Light from one edge is bent one way while light from the other edge is bent the other way at the same instant, so the wobbles **average out** before the light reaches you. Many independent paths cannot all dim at once.",
      "source": {
        "label": "Royal Museums Greenwich — What was the bright object I saw in the sky last night?",
        "url": "https://www.rmg.co.uk/stories/space-astronomy/what-was-bright-object-i-saw-sky-last-night"
      },
      "tags": [
        "l01p1",
        "planets",
        "scintillation"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Venus crescent phase telescopic photograph resolved planetary disc",
        "entityTerm": "Venus",
        "imagePrompt": "A telescopic photograph of Venus showing a clean crescent phase — a resolved disc with a sharp terminator, against a black sky.",
        "alt": "Venus photographed through a telescope as an unmistakable crescent-shaped disc rather than a point of light",
        "depictable": true,
        "credit": "Wikipedia — Jupiter · See Wikimedia Commons",
        "creditUrl": "https://en.wikipedia.org/wiki/Jupiter",
        "subject": "Hubble Space Telescope (OPAL 2024) photograph of Jupiter: a full, richly banded planetary disc with visible cloud belts and the Great Red Spot — a genuine planet clearly resolved as a disc, not a point of light.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-planet-disc-averages-out.webp"
      },
      "uid": "1j7o9eaixibfu"
    },
    {
      "id": "ast-f-planet-still-a-dot",
      "shape": "fact",
      "title": "A Disc You Cannot See",
      "body": "Your eye separates detail only about **one arcminute** — 60 arcseconds — apart, so a planet's 10-to-50-arcsecond disc is still a dot to you. For scale, the Moon and the Sun are each about **half a degree** across: 30 arcminutes, or 1,800 arcseconds. The averaging that stops the twinkle happens in the light before it arrives, not in your eye.",
      "source": {
        "label": "Chandra X-ray Observatory — Scales and Angular Measurement",
        "url": "https://chandra.harvard.edu/photo/scale.html"
      },
      "tags": [
        "l01p1",
        "angular-size",
        "naked-eye"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Venus Jupiter conjunction",
        "imagePrompt": "Documentary-style photograph: Venus and Jupiter shining close together as two sharp, unresolved points of light in a twilight sky. Natural light, no readable text, no logos, no watermarks.",
        "alt": "Venus and Jupiter shining close together as two sharp, unresolved points of light in a twilight sky",
        "credit": "Skatebiker · CC BY-SA 4.0",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:Venus-Jupiter-20230301.jpg",
        "subject": "A clean, uncluttered sunset/twilight sky in orange-to-purple gradient over dark mountain silhouettes, with two bright unresolved points of light close together in the upper-middle of the frame; Wikimedia file titled 'Venus-Jupiter-20230301.jpg', CC BY-SA 4.0.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-planet-still-a-dot.webp"
      },
      "uid": "15jvl00m6zmho"
    },
    {
      "id": "ast-f-low-planet-can-twinkle",
      "shape": "fact",
      "title": "The Rule's Horizon Exception",
      "body": "Looking low in the sky means looking through more air: the **airmass** is 1 straight up and 2 at sixty degrees from vertical. A long enough path overwhelms the averaging a small disc gives you, so a planet near the horizon **can** twinkle — Venus low in the west often scintillates violently. Bright stars down there flash colours too, as the long air path splits their light like a prism.",
      "source": {
        "label": "University of Sheffield PHY217 — Calibrating Photometric Data",
        "url": "https://vikdhillon.staff.shef.ac.uk/teaching/phy217/instruments/phy217_inst_photcal.html"
      },
      "tags": [
        "l01p1",
        "airmass",
        "horizon"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Venus evening star",
        "imagePrompt": "Documentary-style photograph: Venus glowing as a bright point low over the horizon at dusk, the 'evening star'. Natural light, no readable text, no logos, no watermarks.",
        "alt": "Venus glowing as a bright point low over the horizon at dusk, the 'evening star'",
        "credit": "Brocken Inaglory · CC BY-SA 3.0",
        "creditUrl": "https://en.wikipedia.org/wiki/Venus_in_culture",
        "subject": "a twilight photograph over an ocean horizon: one very bright point of light sits low near the skyline with its glow reflected on the water, plus a fainter star higher up in a darkening, star-flecked sky — exactly 'Venus glowing as a bright point low over the horizon at dusk'",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-low-planet-can-twinkle.webp"
      },
      "uid": "1j3g5be17vq9ws"
    },
    {
      "id": "ast-d-airmass",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Airmass"
      },
      "definition": {
        "modality": "text",
        "value": "How much atmosphere a beam crosses on its way down: 1 looking straight up, 2 at sixty degrees from vertical, far more at the horizon"
      },
      "source": {
        "label": "University of Sheffield PHY217 — Calibrating Photometric Data",
        "url": "https://vikdhillon.staff.shef.ac.uk/teaching/phy217/instruments/phy217_inst_photcal.html"
      },
      "tags": [
        "l01p1",
        "airmass",
        "atmosphere"
      ],
      "uid": "uburxo8djae2"
    },
    {
      "id": "ast-p-proxima-centauri-distance",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Proxima Centauri"
      },
      "sideB": {
        "modality": "text",
        "value": "The nearest star after the Sun, 4.25 light years away",
        "short": "4.25 light years away"
      },
      "source": {
        "label": "NASA Imagine the Universe — The Nearest Star",
        "url": "https://imagine.gsfc.nasa.gov/features/cosmic/nearest_star_info.html"
      },
      "tags": [
        "l01p1",
        "stars",
        "distance"
      ],
      "uid": "lwdmg41xklyce"
    },
    {
      "id": "ast-p-r-doradus-disc",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "R Doradus"
      },
      "sideB": {
        "modality": "text",
        "value": "The widest stellar disc measured from Earth, 0.057 arcseconds",
        "short": "A 0.057-arcsecond disc"
      },
      "source": {
        "label": "ESO — The Biggest Star in the Sky (eso9706)",
        "url": "https://www.eso.org/public/news/eso9706/"
      },
      "tags": [
        "l01p1",
        "stars",
        "angular-size"
      ],
      "uid": "1h3j8m1u46b6"
    },
    {
      "id": "ast-q-why-stars-twinkle",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Why does one light in the night sky flicker while another holds steady?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Brighter, not fainter"
        },
        {
          "modality": "text",
          "value": "Hotter, not cooler"
        },
        {
          "modality": "text",
          "value": "Burning, not reflecting"
        },
        {
          "modality": "text",
          "value": "A point, not a disc"
        }
      ],
      "correctIndex": 3,
      "explanation": "A point sends one narrow beam, which moving air bends in and out of your eye; a disc sends many, and they cannot all dim at once. Burning versus reflecting is a real difference but not this one. Brighter and hotter change nothing: a faint planet still holds steady.",
      "source": {
        "label": "University of Wisconsin–Madison — Why do stars appear to twinkle in the night sky?",
        "url": "https://news.wisc.edu/curiosities-why-do-stars-appear-to-twinkle-in-the-night-sky/"
      },
      "tags": [
        "l01p1",
        "twinkling",
        "distance"
      ],
      "uid": "pbrzcf1z0xtrb"
    },
    {
      "id": "ast-q-star-through-telescope",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Aim the largest amateur telescope at a star. What do you get?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Visible surface detail"
        },
        {
          "modality": "text",
          "value": "A disc with mottled markings"
        },
        {
          "modality": "text",
          "value": "A brighter point of light"
        },
        {
          "modality": "text",
          "value": "A small round disc"
        }
      ],
      "correctIndex": 2,
      "explanation": "Even Hubble separates detail only to about 0.1 arcseconds, nearly twice the width of the largest stellar disc there is. So no small round disc appears, no surface detail resolves and no mottled markings show. Magnification adds brightness, not resolution.",
      "source": {
        "label": "Chandra X-ray Observatory — Scales and Angular Measurement",
        "url": "https://chandra.harvard.edu/photo/scale.html"
      },
      "tags": [
        "l01p1",
        "telescopes",
        "resolution"
      ],
      "uid": "16lz9u91ne4091"
    },
    {
      "id": "czr-ast-d-airmass",
      "shape": "cloze",
      "derivedFrom": "ast-d-airmass",
      "template": "___ — How much atmosphere a beam crosses on its way down: 1 looking straight up, 2 at sixty degrees from vertical, far more at the horizon",
      "answer": "Airmass",
      "distractors": [
        "Apparent magnitude",
        "Solar mass",
        "Escape speed"
      ],
      "explanation": "Airmass is how much atmosphere a beam crosses on its way down. Apparent magnitude, the closest of the alternatives, is how bright a thing looks from Earth, on a ranking inherited from Hipparchus.",
      "source": {
        "label": "University of Sheffield PHY217 — Calibrating Photometric Data",
        "url": "https://vikdhillon.staff.shef.ac.uk/teaching/phy217/instruments/phy217_inst_photcal.html"
      },
      "tags": [
        "l01p1",
        "airmass",
        "atmosphere",
        "derived"
      ],
      "uid": "j5tqp1ldkq0h"
    },
    {
      "id": "tfr-ast-d-airmass",
      "shape": "trueFalse",
      "derivedFrom": "ast-d-airmass",
      "statement": "Airmass — how much atmosphere a beam crosses on its way down.",
      "isTrue": true,
      "why": "Airmass is how much atmosphere a beam crosses on its way down, which is why a star low over the horizon looks dimmer and redder than the same star overhead. The Chandrasekhar limit is a mass ceiling instead: the heaviest a white dwarf can be, about 1.4 solar masses.",
      "source": {
        "label": "University of Sheffield PHY217 — Calibrating Photometric Data",
        "url": "https://vikdhillon.staff.shef.ac.uk/teaching/phy217/instruments/phy217_inst_photcal.html"
      },
      "tags": [
        "l01p1",
        "airmass",
        "atmosphere",
        "derived"
      ],
      "uid": "36nob11nxoix9"
    },
    {
      "id": "ast-f-iss-is-a-mirror",
      "shape": "fact",
      "title": "A Mirror, Not a Lamp",
      "body": "The **International Space Station** carries no lights you can see from the ground. It is visible purely as **reflected sunlight**, mostly off about **2,500 square metres** of solar array — the same reason we can see the Moon. Cabin lighting is far too faint to reach you, so what crosses the sky is the Sun's light, bounced.",
      "factVariant": "image-heavy",
      "imageCaption": "Every photon you see from the station started at the Sun.",
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "International Space Station solar array wings lit by sunlight in orbit",
        "entityTerm": "International Space Station",
        "imagePrompt": "An orbital photograph of the International Space Station dominated by its large solar array wings in full sunlight against black space.",
        "alt": "The complete International Space Station seen from a departing spacecraft, its eight large solar array wings and white radiator panels sunlit against black space, with the Russian segment and…",
        "depictable": true,
        "credit": "Wikipedia — International Space Station · See Wikimedia Commons",
        "creditUrl": "https://en.wikipedia.org/wiki/International_Space_Station",
        "subject": "The complete International Space Station seen from a departing spacecraft, its eight large solar array wings and white radiator panels sunlit against black space, with the Russian segment and Nauka module at the bottom and the cloud-covered curve of Earth below. This is the NASA photograph from the ",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-iss-is-a-mirror.webp"
      },
      "source": {
        "label": "NASA — Spot the Station Frequently Asked Questions",
        "url": "https://www.nasa.gov/missions/station/spot-the-station-frequently-asked-questions/"
      },
      "tags": [
        "l01p2",
        "iss",
        "reflected-light"
      ],
      "uid": "1a79p3714mfqgp"
    },
    {
      "id": "ast-f-iss-speed-and-altitude",
      "shape": "fact",
      "title": "Four Hundred Kilometres Up",
      "body": "The station orbits about **400 kilometres** above the ground — closer to you than most countries are, a couple of hours' drive straight up. It travels at roughly **28,000 kilometres per hour** and circles the Earth in about **90 minutes**: sixteen circuits a day, and sixteen sunrises for the crew. Nothing is pushing it along. That is simply the speed a circular orbit at 400 km requires.",
      "source": {
        "label": "ESA — Where is the International Space Station?",
        "url": "https://www.esa.int/Science_Exploration/Human_and_Robotic_Exploration/International_Space_Station/Where_is_the_International_Space_Station"
      },
      "tags": [
        "l01p2",
        "iss",
        "orbit"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "International Space Station photographed in orbit above the curve of the Earth",
        "entityTerm": "International Space Station",
        "imagePrompt": "The International Space Station photographed from a departing spacecraft with the curved, cloud-flecked limb of Earth filling the background.",
        "alt": "A photograph taken from aboard the International Space Station looking down at Earth: a SpaceX Dragon cargo capsule berthed to the station in the foreground with its dark-blue trunk solar arrays…",
        "depictable": true,
        "credit": "Pexels · SpaceX · Pexels License",
        "creditUrl": "https://www.pexels.com/photo/satellite-view-of-earth-586072/",
        "subject": "A photograph taken from aboard the International Space Station looking down at Earth: a SpaceX Dragon cargo capsule berthed to the station in the foreground with its dark-blue trunk solar arrays, the Canadarm2 robotic arm (with its \"Canada\" wordmark) above it, one of the ISS's gold solar array wings",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-iss-speed-and-altitude.webp"
      },
      "uid": "zmhebuz0a4pk"
    },
    {
      "id": "ast-f-meteor-lasts-seconds",
      "shape": "fact",
      "title": "Over in a Second",
      "body": "A **meteor** is a grain of dust or a small rock meeting the atmosphere at between **11 and 72 kilometres per second**, burning about **80 to 120 kilometres** up. It is over in a few seconds — usually less — and that duration is what separates it from every other moving light. Most shooting stars are sand-grain debris that burns away entirely; only a rare, larger one drops anything to the ground.",
      "source": {
        "label": "EarthSky — How high up are meteors when they begin to glow?",
        "url": "https://earthsky.org/space/at-what-altitude-do-meteors-become-incandescent/"
      },
      "tags": [
        "l01p2",
        "meteors",
        "atmosphere"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "a single bright meteor streak in a dark starry sky",
        "imagePrompt": "A night-sky photograph in which a single meteor cuts a short, bright, tapering streak across otherwise steady stars.",
        "alt": "One bright meteor drawn as a short, tapering streak across the sky",
        "depictable": true,
        "credit": "Pexels · Achraf Alan · Pexels License",
        "creditUrl": "https://www.pexels.com/photo/photo-of-shooting-star-during-night-time-1477156/",
        "subject": "A single bright, warm orange-red tapering streak arcing across a mostly empty dark sky, with a soft horizon glow at the bottom — clean, unambiguous, one streak only.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-meteor-lasts-seconds.webp"
      },
      "uid": "10v6y5ygbkljq"
    },
    {
      "id": "ast-f-orbit-is-crowded",
      "shape": "fact",
      "title": "Forty Thousand Tracked Objects",
      "body": "Space surveillance networks track about **40,000 objects** in Earth orbit, of which roughly **11,000 are working payloads**. Seeing several moving points in an hour is no longer unusual — under a dark sky it is the normal experience. The count keeps climbing, so treat these figures as dated rather than fixed.",
      "source": {
        "label": "ESA — Space Environment Report 2025",
        "url": "https://www.esa.int/Space_Safety/Space_Debris/ESA_Space_Environment_Report_2025"
      },
      "tags": [
        "l01p2",
        "satellites",
        "orbit"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "long exposure night sky crossed by many satellite trails",
        "imagePrompt": "A long-exposure night sky photograph crossed by several straight, evenly bright satellite trails at different angles over a dark landscape.",
        "alt": "A long-exposure night sky ruled by several straight satellite trails crossing the star field",
        "depictable": true,
        "credit": "International Gemini Observatory/NOIRLab/NSF/AURA/J. Warner (Openverse) · by 4.0",
        "creditUrl": "https://commons.wikimedia.org/w/index.php?curid=182244888",
        "subject": "NOIRLab/Gemini Observatory photo 'Stars and Satellites over Gemini North': a long star-trail composite over the Gemini North dome on Mauna Kea, with dense curved star-trail arcs crossed by a lattice of straight satellite trails and one bright flare/meteor streak -- matches the alt text directly",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-orbit-is-crowded.webp"
      },
      "uid": "1xzf2nj1xk7kt"
    },
    {
      "id": "ast-d-fireball",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Fireball"
      },
      "definition": {
        "modality": "text",
        "value": "A meteor brighter than magnitude −4, about as bright as Venus at its best — and still over in seconds, so brightness alone never tells it from a satellite"
      },
      "source": {
        "label": "American Meteor Society — Fireball FAQs",
        "url": "https://www.amsmeteors.org/fireballs/faqf/"
      },
      "tags": [
        "l01p2",
        "meteors",
        "brightness"
      ],
      "uid": "1nro1t1mxghcv"
    },
    {
      "id": "ast-p-aircraft-position-lights",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Aircraft light rules"
      },
      "sideB": {
        "modality": "text",
        "value": "Red on the left, green on the right, white to the rear",
        "short": "Red left, green right"
      },
      "source": {
        "label": "14 CFR § 25.1385 — Position light system installation",
        "url": "https://www.law.cornell.edu/cfr/text/14/25.1385"
      },
      "tags": [
        "l01p2",
        "aircraft",
        "identification"
      ],
      "uid": "17tk3h31prlo0x"
    },
    {
      "id": "ast-p-satellite-pass-length",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Satellite pass length"
      },
      "sideB": {
        "modality": "text",
        "value": "About two minutes from one horizon to the other"
      },
      "source": {
        "label": "Royal Museums Greenwich — What was the bright object I saw in the sky last night?",
        "url": "https://www.rmg.co.uk/stories/space-astronomy/what-was-bright-object-i-saw-sky-last-night"
      },
      "tags": [
        "l01p2",
        "satellites",
        "identification"
      ],
      "uid": "1p7iwwb157dp1d"
    },
    {
      "id": "ast-q-iss-fades-mid-sky",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "A bright pass of the space station fades to nothing halfway across the sky. Why?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Its arrays turned from the Sun"
        },
        {
          "modality": "text",
          "value": "Its own lights were switched off"
        },
        {
          "modality": "text",
          "value": "It has moved too far to see"
        },
        {
          "modality": "text",
          "value": "It flies into Earth's shadow"
        }
      ],
      "correctIndex": 3,
      "explanation": "It shines only by reflected sunlight, and halfway across the sky it crosses into Earth's shadow. Its arrays track the Sun continuously and turning them would not darken the hull; it carries no lights to switch off; and it is no farther away than a moment earlier.",
      "source": {
        "label": "NASA — Spot the Station Frequently Asked Questions",
        "url": "https://www.nasa.gov/missions/station/spot-the-station-frequently-asked-questions/"
      },
      "tags": [
        "l01p2",
        "iss",
        "shadow"
      ],
      "uid": "jzl13kxzk78w"
    },
    {
      "id": "ast-q-satellite-signature",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "A moving light crosses the sky. Which sign marks it as a satellite?"
      },
      "options": [
        {
          "modality": "text",
          "value": "A streak gone in one second"
        },
        {
          "modality": "text",
          "value": "Red and green flashes"
        },
        {
          "modality": "text",
          "value": "A steady point, holding course"
        },
        {
          "modality": "text",
          "value": "A brief hover, then a bank away"
        }
      ],
      "correctIndex": 2,
      "explanation": "Red and green flashes are the position lights an aircraft must show at night. Hovering and then banking away is an aircraft turning as it passes. A streak gone in a second is a meteor burning up. Only an orbit gives an unblinking point on a straight track.",
      "source": {
        "label": "Royal Museums Greenwich — What was the bright object I saw in the sky last night?",
        "url": "https://www.rmg.co.uk/stories/space-astronomy/what-was-bright-object-i-saw-sky-last-night"
      },
      "tags": [
        "l01p2",
        "satellites",
        "identification"
      ],
      "uid": "j8d4unm1sr9z"
    },
    {
      "id": "czr-ast-d-fireball",
      "shape": "cloze",
      "derivedFrom": "ast-d-fireball",
      "template": "___ — A meteor brighter than magnitude −4, about as bright as Venus at its best — and still over in seconds, so brightness alone never tells it from a satellite",
      "answer": "Fireball",
      "distractors": [
        "Ice giant",
        "Rock comet",
        "Dwarf planet"
      ],
      "explanation": "Fireball is a meteor brighter than magnitude −4, about as bright as Venus at its best. Ice giant, the closest of the alternatives, is a giant planet whose bulk is a hot fluid of water, methane and ammonia over a rocky core, not the hydrogen and helium of a gas giant.",
      "source": {
        "label": "American Meteor Society — Fireball FAQs",
        "url": "https://www.amsmeteors.org/fireballs/faqf/"
      },
      "tags": [
        "l01p2",
        "meteors",
        "brightness",
        "derived"
      ],
      "uid": "td4dc417fcq6c"
    },
    {
      "id": "tfr-ast-d-fireball",
      "shape": "trueFalse",
      "derivedFrom": "ast-d-fireball",
      "statement": "Fireball — a galaxy with no disc, no arms and no smooth ellipse.",
      "isTrue": false,
      "why": "A fireball is a meteor brighter than magnitude −4, about as bright as Venus at its best and bright enough to throw a shadow. An irregular galaxy is a shape class: a galaxy with no disc, no arms and no smooth ellipse, often pulled out of shape by a passing neighbour.",
      "source": {
        "label": "American Meteor Society — Fireball FAQs",
        "url": "https://www.amsmeteors.org/fireballs/faqf/"
      },
      "tags": [
        "l01p2",
        "meteors",
        "brightness",
        "derived"
      ],
      "whyOptions": [
        "Ice giant",
        "Irregular galaxy",
        "Rock comet"
      ],
      "whyCorrectIndex": 1,
      "uid": "1opt5frb3f07n"
    },
    {
      "id": "ast-f-magnitude-runs-backwards",
      "shape": "fact",
      "title": "A Scale Running Backwards",
      "body": "**Apparent magnitude** runs backwards: the smaller the number, the brighter the object, and the brightest things carry **negative** numbers. It is a two-thousand-year-old accident. Hipparchus called the brightest stars *first magnitude* and the faintest he could see *sixth*, and astronomy kept his ranking — so negative does not mean below zero brightness, only brighter than the old first rank.",
      "source": {
        "label": "Penn State ASTRO 801 — The Magnitude System",
        "url": "https://courses.ems.psu.edu/astro801/content/l4_p5.html"
      },
      "tags": [
        "l01p3",
        "magnitude",
        "history"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Orion constellation photograph showing stars of clearly different brightness",
        "entityTerm": "Orion (constellation)",
        "imagePrompt": "A photograph of the constellation Orion in which the brightest stars render as large discs and the faintest as small points, making the brightness ranking obvious.",
        "alt": "A single very bright star with cross-shaped diffraction spikes and a faint blue-white halo, centred in a dark sky scattered with hundreds of far fainter stars.",
        "depictable": true,
        "subject": "A single very bright star with cross-shaped diffraction spikes and a faint blue-white halo, centred in a dark sky scattered with hundreds of far fainter stars. Not Orion: no belt and no Betelgeuse/Rigel pair are in frame; the Pexels credit names no star.",
        "credit": "Pexels · A bright star shines among countless stars in the vast, dark night sky.",
        "creditUrl": "https://www.pexels.com/photo/bright-star-in-the-vast-starry-night-sky-33931044/",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-magnitude-runs-backwards.webp"
      },
      "uid": "1jp2dnzihgat7"
    },
    {
      "id": "ast-f-five-magnitudes-hundredfold",
      "shape": "fact",
      "title": "Five Steps, One Hundred Times",
      "body": "The scale is **logarithmic**: one magnitude is a factor of about **2.512** in brightness, and five magnitudes is a factor of exactly **100**. Each step is the same ratio, not the same amount — which is why the gaps are larger than they look. The Sun at −26.7 sits 32.7 magnitudes above the naked-eye limit of +6.0, a factor of roughly **twelve trillion** — and it is the one object on that scale you must never look at directly.",
      "factVariant": "image-heavy",
      "imageCaption": "Each step down the scale multiplies the light by about two and a half.",
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "apparent magnitude logarithmic brightness ladder diagram",
        "imagePrompt": "A clean vertical ladder diagram of apparent magnitude with rungs labelled from about -27 to +6, each step annotated as x2.512 and a bracket showing five steps equalling x100. Flat vector, light background.",
        "alt": "Ladder diagram of the magnitude scale, each rung a factor of 2.512 in brightness and five rungs a factor of one hundred",
        "depictable": true,
        "allowGenerated": true
      },
      "source": {
        "label": "Case Western Reserve University ASTR 221 — The Magnitude Scale",
        "url": "https://burro.case.edu/Academics/Astr221/Light/magscale.html"
      },
      "tags": [
        "l01p3",
        "magnitude",
        "logarithmic"
      ],
      "uid": "m3a0b81cu0vte"
    },
    {
      "id": "ast-f-only-2500-stars",
      "shape": "fact",
      "title": "Fewer Stars Than You Think",
      "body": "Under a genuinely dark sky the naked-eye limit is around magnitude **+6.0 to +6.5**, which puts perhaps **2,500 stars** above your horizon at any moment. The famous *millions of stars* is wrong by three orders of magnitude. Under city light the limit falls far enough that most of those stars simply vanish.",
      "source": {
        "label": "Las Cumbres Observatory — Apparent Magnitude",
        "url": "https://lco.global/spacebook/distance/what-apparent-magnitude/"
      },
      "tags": [
        "l01p3",
        "magnitude",
        "dark-sky"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "the night sky as seen with the unaided eye from a dark rural site",
        "imagePrompt": "A wide naked-eye view of a genuinely dark rural night sky, stars sparse and individually countable rather than a dense telescopic star field.",
        "alt": "A wide-field night-sky photograph: a deep blue-black sky scattered with pinpoint stars, with a faint hazy band of the Milky Way running up the left side.",
        "depictable": true,
        "subject": "A wide-field night-sky photograph: a deep blue-black sky scattered with pinpoint stars, with a faint hazy band of the Milky Way running up the left side. No ground, horizon, text, or logos in frame.",
        "credit": "Pexels · A captivating view of a dense star field against a clear night sky, showcasing the vastness of space.",
        "creditUrl": "https://www.pexels.com/photo/dense-field-star-on-clear-night-sky-18066238/",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-only-2500-stars.webp"
      },
      "uid": "fakmwp2m3g5d"
    },
    {
      "id": "ast-f-ecliptic-and-daily-drift",
      "shape": "fact",
      "title": "One Line, One Daily Turn",
      "body": "The whole sky drifts east to west at about **15 degrees an hour** — 360 degrees in 24 hours — and that is Earth turning, not the sky. The Sun traces a path called the **ecliptic**: the plane of Earth's orbit, tilted **23.4 degrees** to the celestial equator. The planets orbit near that plane, and the Moon's orbit is tipped only about 5 degrees, so they all appear along one broad line.",
      "source": {
        "label": "NASA — Basics of Space Flight, Chapter 2: Reference Systems",
        "url": "https://science.nasa.gov/learn/basics-of-space-flight/chapter2-2/"
      },
      "tags": [
        "l01p3",
        "ecliptic",
        "diurnal-motion"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "circumpolar star trails circling the celestial pole long exposure",
        "imagePrompt": "A long-exposure photograph of concentric circular star trails centred on the celestial pole above a dark, simple landscape.",
        "alt": "A long-exposure night photograph of concentric star trails arcing around the celestial pole (centre of rotation at upper left of frame), above a flat horizon with an orange-pink twilight glow and…",
        "depictable": true,
        "credit": "Pexels · Stunning long-exposure capture of star trails illuminating the night sky over a colorful horizon.",
        "creditUrl": "https://www.pexels.com/photo/star-trails-over-a-colorful-horizon-at-night-35647006/",
        "subject": "A long-exposure night photograph of concentric star trails arcing around the celestial pole (centre of rotation at upper left of frame), above a flat horizon with an orange-pink twilight glow and a line of distant ground lights.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-ecliptic-and-daily-drift.webp"
      },
      "uid": "1k4r6vj13rharf"
    },
    {
      "id": "ast-d-apparent-magnitude",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Apparent magnitude"
      },
      "definition": {
        "modality": "text",
        "value": "How bright a thing looks from Earth, on a ranking inherited from Hipparchus — a smaller number means brighter, negative means brighter still, and five steps is a factor of exactly 100"
      },
      "source": {
        "label": "Las Cumbres Observatory — Apparent Magnitude",
        "url": "https://lco.global/spacebook/distance/what-apparent-magnitude/"
      },
      "tags": [
        "l01p3",
        "magnitude",
        "brightness"
      ],
      "uid": "1pfclcgbkvd22"
    },
    {
      "id": "ast-q-magnitude-faintest-object",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Which of these four sends the least light to your eye?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Venus, at −4.4"
        },
        {
          "modality": "text",
          "value": "Vega, at 0.0"
        },
        {
          "modality": "text",
          "value": "Sirius, at −1.46"
        },
        {
          "modality": "text",
          "value": "A star at magnitude +6.0"
        }
      ],
      "correctIndex": 3,
      "explanation": "Magnitude runs backwards: the larger the number, the fainter the object. +6.0 is the naked-eye limit and the faintest here. Vega at 0.0 defines the zero point, Sirius at -1.46 is the brightest star in the night sky, and Venus at -4.4 is brighter still.",
      "source": {
        "label": "Case Western Reserve University ASTR 221 — The Magnitude Scale",
        "url": "https://burro.case.edu/Academics/Astr221/Light/magscale.html"
      },
      "tags": [
        "l01p3",
        "magnitude",
        "brightness"
      ],
      "uid": "13rwvf15nhdrl"
    },
    {
      "id": "ast-n-magnitude-sun",
      "shape": "numeric",
      "prompt": {
        "modality": "text",
        "value": "The Sun — never view it directly, with or without optics"
      },
      "value": -26.7,
      "unit": "magnitude",
      "tolerance": 0.2,
      "source": {
        "label": "Las Cumbres Observatory — Apparent Magnitude",
        "url": "https://lco.global/spacebook/distance/what-apparent-magnitude/"
      },
      "tags": [
        "l01p3",
        "magnitude",
        "sun"
      ],
      "uid": "jf1q4cmh9m82"
    },
    {
      "id": "ast-n-magnitude-full-moon",
      "shape": "numeric",
      "prompt": {
        "modality": "text",
        "value": "The full Moon"
      },
      "value": -12.6,
      "unit": "magnitude",
      "tolerance": 0.2,
      "source": {
        "label": "Las Cumbres Observatory — Apparent Magnitude",
        "url": "https://lco.global/spacebook/distance/what-apparent-magnitude/"
      },
      "tags": [
        "l01p3",
        "magnitude",
        "moon"
      ],
      "uid": "uf10hl1hv5cgn"
    },
    {
      "id": "ast-n-magnitude-venus-brightest",
      "shape": "numeric",
      "prompt": {
        "modality": "text",
        "value": "Venus at its brightest"
      },
      "value": -4.4,
      "unit": "magnitude",
      "tolerance": 0.3,
      "source": {
        "label": "Las Cumbres Observatory — Apparent Magnitude",
        "url": "https://lco.global/spacebook/distance/what-apparent-magnitude/"
      },
      "tags": [
        "l01p3",
        "magnitude",
        "venus"
      ],
      "uid": "1m0yblb1bpifih"
    },
    {
      "id": "ast-n-magnitude-sirius",
      "shape": "numeric",
      "prompt": {
        "modality": "text",
        "value": "Sirius, the brightest night star"
      },
      "value": -1.46,
      "unit": "magnitude",
      "tolerance": 0.2,
      "source": {
        "label": "Case Western Reserve University ASTR 221 — The Magnitude Scale",
        "url": "https://burro.case.edu/Academics/Astr221/Light/magscale.html"
      },
      "tags": [
        "l01p3",
        "magnitude",
        "sirius"
      ],
      "uid": "1c6wuhk1rar32"
    },
    {
      "id": "ast-n-magnitude-vega",
      "shape": "numeric",
      "prompt": {
        "modality": "text",
        "value": "Vega, the zero point of the scale"
      },
      "value": 0,
      "unit": "magnitude",
      "tolerance": 0.1,
      "source": {
        "label": "Case Western Reserve University ASTR 221 — The Magnitude Scale",
        "url": "https://burro.case.edu/Academics/Astr221/Light/magscale.html"
      },
      "tags": [
        "l01p3",
        "magnitude",
        "vega"
      ],
      "uid": "zm2qlkid6fl4"
    },
    {
      "id": "ast-n-magnitude-naked-eye-limit",
      "shape": "numeric",
      "prompt": {
        "modality": "text",
        "value": "The naked-eye limit under a dark sky"
      },
      "value": 6,
      "unit": "magnitude",
      "tolerance": 0.5,
      "source": {
        "label": "Las Cumbres Observatory — Apparent Magnitude",
        "url": "https://lco.global/spacebook/distance/what-apparent-magnitude/"
      },
      "tags": [
        "l01p3",
        "magnitude",
        "dark-sky"
      ],
      "uid": "fh627pl1tblt"
    },
    {
      "id": "czr-ast-d-apparent-magnitude",
      "shape": "cloze",
      "derivedFrom": "ast-d-apparent-magnitude",
      "template": "___ — How bright a thing looks from Earth, on a ranking inherited from Hipparchus — a smaller number means brighter, negative means brighter still, and five steps is a factor of exactly 100",
      "answer": "Apparent magnitude",
      "distractors": [
        "Airmass",
        "Solar mass",
        "Escape speed"
      ],
      "explanation": "Apparent magnitude is how bright a thing looks from Earth, on a ranking inherited from Hipparchus. Airmass, the closest of the alternatives, is how much atmosphere a beam crosses on its way down.",
      "source": {
        "label": "Las Cumbres Observatory — Apparent Magnitude",
        "url": "https://lco.global/spacebook/distance/what-apparent-magnitude/"
      },
      "tags": [
        "l01p3",
        "magnitude",
        "brightness",
        "derived"
      ],
      "uid": "ipn9n3blwj9z"
    },
    {
      "id": "ast-f-moon-half-lit",
      "shape": "fact",
      "title": "Half Lit, Always",
      "body": "The Sun lights exactly **half** the Moon at every moment — one hemisphere in daylight, one in darkness, no exceptions. A **phase** is simply how much of that permanently lit half is turned toward you. Earth's shadow has nothing to do with it: the shadow reaches the Moon only during a **lunar eclipse**, and those do not happen every month. Phases do.",
      "factVariant": "image-heavy",
      "imageCaption": "Nothing about the Moon changes during the month; your line of sight does.",
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "Moon phases orbit diagram with sunlight arriving from one direction",
        "imagePrompt": "Flat vector diagram: the Moon at eight orbital positions around Earth, parallel sunlight arriving from one side so exactly half of each Moon is lit, with the phase as seen from Earth drawn beside each position.",
        "alt": "Diagram of the Moon at eight points around its orbit with sunlight arriving from one side, showing the same lit half viewed from different angles",
        "depictable": true,
        "allowGenerated": true
      },
      "source": {
        "label": "NASA — Moon Phases",
        "url": "https://science.nasa.gov/moon/moon-phases/"
      },
      "tags": [
        "l02p1",
        "moon",
        "phases"
      ],
      "uid": "9r6f8r10emg5r"
    },
    {
      "id": "ast-f-moon-two-months",
      "shape": "fact",
      "title": "Two Months, One Orbit",
      "body": "One lap of the Moon against the background stars takes **27.322 days** — the sidereal month, its true orbital period. New Moon to new Moon takes **29.530589 days**, about 2.2 days longer. Phases are measured against the Sun, and Earth carries the Moon along its own orbit meanwhile, so after one full lap the Moon still has further to travel before it lines up with the Sun again.",
      "source": {
        "label": "JPL Solar System Dynamics — Planetary Satellite Mean Elements",
        "url": "https://ssd.jpl.nasa.gov/sats/elem/"
      },
      "tags": [
        "l02p1",
        "moon",
        "orbit"
      ],
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "sidereal versus synodic month diagram Moon Earth Sun alignment",
        "imagePrompt": "Two-panel flat vector diagram: panel one shows the Moon completing 27.3 days back to the same background star; panel two shows Earth having moved along its orbit so the Moon must travel further to line up with the Sun again at 29.5 days.",
        "alt": "Diagram contrasting one lap of the Moon against the stars with the longer run back to the same alignment with the Sun",
        "depictable": true,
        "allowGenerated": true
      },
      "uid": "3fndgm2328ac"
    },
    {
      "id": "ast-f-moon-far-side",
      "shape": "fact",
      "title": "The Far Side Is Sunlit",
      "body": "The Moon is **tidally locked**: it turns once on its axis for every orbit of Earth, which is exactly why the same face stays pointed at us. It is rotating, not frozen. And the **far side** is not a dark side — it gets as much sunlight as the near side does. We simply never see it from here.",
      "source": {
        "label": "NASA — Moon Phases",
        "url": "https://science.nasa.gov/moon/moon-phases/"
      },
      "tags": [
        "l02p1",
        "moon",
        "rotation"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "far side of the Moon photographed by Lunar Reconnaissance Orbiter",
        "entityTerm": "Far side of the Moon",
        "imagePrompt": "An orbital photograph of the Moon's far side in daylight, densely cratered highlands, no large dark maria, against black space.",
        "alt": "The Moon's far side in full sunlight, heavily cratered and without the dark maria of the near side",
        "depictable": true,
        "credit": "Wikipedia — Far side of the Moon · See Wikimedia Commons",
        "creditUrl": "https://en.wikipedia.org/wiki/Far_side_of_the_Moon",
        "subject": "Full lunar disc in full sunlight, overwhelmingly cratered highland terrain with only two small dark patches (consistent with Mare Moscoviense and Mare Ingenii) and a bright-rayed crater near center — the lead image of Wikipedia's 'Far side of the Moon' article, matching the alt text closely.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-moon-far-side.webp"
      },
      "uid": "1uswijeq2clyk"
    },
    {
      "id": "ast-f-moon-tilt-nodes",
      "shape": "fact",
      "title": "Five Degrees Off Target",
      "body": "The Moon's orbit is tilted **5.16 degrees** to Earth's orbital plane. At the Moon's distance that small angle throws its shadow thousands of kilometres above or below Earth, so most new Moons produce nothing at all. The two points where the tilted orbit crosses are the **nodes**, and an eclipse needs the right phase *and* the Moon near a node — a coincidence confined to an **eclipse season**, with midpoints 173.3 days apart.",
      "source": {
        "label": "NASA — Why Do Eclipses Happen?",
        "url": "https://science.nasa.gov/eclipses/geometry/"
      },
      "tags": [
        "l02p1",
        "moon",
        "eclipse-geometry"
      ],
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "lunar orbit five degree tilt nodes eclipse season diagram",
        "imagePrompt": "Flat vector diagram showing the Moon's orbital plane inclined about five degrees to the ecliptic, the two crossing points labelled as nodes, and the Moon's shadow cone passing above and below Earth at other times.",
        "alt": "A black-and-white telephoto photograph of the full Moon (Earth's Moon) against a black sky, showing the dark maria of the near side and the bright rayed crater Tycho.",
        "depictable": true,
        "allowGenerated": true,
        "subject": "A black-and-white telephoto photograph of the full Moon (Earth's Moon) against a black sky, showing the dark maria of the near side and the bright rayed crater Tycho.",
        "credit": "Pexels · Black and white image of the full moon showcasing detailed craters, captured over Varanasi.",
        "creditUrl": "https://www.pexels.com/photo/full-moon-28284726/",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-moon-tilt-nodes.webp"
      },
      "uid": "114td2d13in00p"
    },
    {
      "id": "ast-d-synodic-month",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Synodic month"
      },
      "definition": {
        "modality": "text",
        "value": "The 29.53-day round trip from one new Moon to the next, timed against the Sun rather than against the background stars"
      },
      "curatedDistractors": [
        "Sidereal month",
        "Draconic month",
        "Anomalistic month"
      ],
      "source": {
        "label": "NASA GSFC — Periodicity of Solar Eclipses",
        "url": "https://eclipse.gsfc.nasa.gov/SEsaros/SEperiodicity.html"
      },
      "tags": [
        "l02p1",
        "moon",
        "lunar-months"
      ],
      "uid": "4gxwnydj55go"
    },
    {
      "id": "ast-p-moon-tidal-lock",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Tidally locked"
      },
      "sideB": {
        "modality": "text",
        "value": "One turn on its axis for every trip around Earth"
      },
      "source": {
        "label": "NASA — Moon Phases",
        "url": "https://science.nasa.gov/moon/moon-phases/"
      },
      "tags": [
        "l02p1",
        "moon",
        "rotation"
      ],
      "uid": "1mfjtk41577odw"
    },
    {
      "id": "ast-p-moon-perigee",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Perigee"
      },
      "sideB": {
        "modality": "text",
        "value": "The Moon's closest approach, a mean 363,300 km"
      },
      "source": {
        "label": "JPL Solar System Dynamics — Planetary Satellite Mean Elements",
        "url": "https://ssd.jpl.nasa.gov/sats/elem/"
      },
      "tags": [
        "l02p1",
        "moon",
        "distance"
      ],
      "uid": "1g1pczd143hsy9"
    },
    {
      "id": "ast-q-moon-first-quarter",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "At first quarter, how much of the Moon's visible face is lit?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Half"
        },
        {
          "modality": "text",
          "value": "Three quarters"
        },
        {
          "modality": "text",
          "value": "All of it"
        },
        {
          "modality": "text",
          "value": "One quarter"
        }
      ],
      "correctIndex": 0,
      "explanation": "The name counts the orbit, not the disc: one quarter of the cycle is complete while exactly half the face is lit. A quarter-lit face and a three-quarter-lit face are the crescent and gibbous phases, and a fully lit face is the full Moon.",
      "source": {
        "label": "NASA — Moon Phases",
        "url": "https://science.nasa.gov/moon/moon-phases/"
      },
      "tags": [
        "l02p1",
        "moon",
        "phase-names"
      ],
      "uid": "1esrrald7ahg7"
    },
    {
      "id": "ast-q-moon-phase-cause",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "What decides the Moon's shape on a given night?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Its dark side rotating into view"
        },
        {
          "modality": "text",
          "value": "How much of the lit half shows"
        },
        {
          "modality": "text",
          "value": "Earth's shadow crossing it"
        },
        {
          "modality": "text",
          "value": "The Sun moving round behind it"
        }
      ],
      "correctIndex": 1,
      "explanation": "Earth's shadow reaches the Moon only at a lunar eclipse, not every month; cloud hides the Moon rather than reshaping it; and there is no permanently dark side to rotate into view. Only your line of sight on the lit half changes.",
      "source": {
        "label": "NASA — Moon Phases",
        "url": "https://science.nasa.gov/moon/moon-phases/"
      },
      "tags": [
        "l02p1",
        "moon",
        "phases"
      ],
      "uid": "1qjm8rjjvznt5"
    },
    {
      "id": "czr-ast-d-synodic-month",
      "shape": "cloze",
      "derivedFrom": "ast-d-synodic-month",
      "template": "___ — The 29.53-day round trip from one new Moon to the next, timed against the Sun rather than against the background stars",
      "answer": "Synodic month",
      "distractors": [
        "Equinox",
        "Solar flare",
        "Sol"
      ],
      "explanation": "Synodic month is the 29.53-day round trip from one new Moon to the next, timed against the Sun rather than against the background stars. Equinox, the closest of the alternatives, is a point where the ecliptic crosses the celestial equator, with the axis leaning neither toward nor away from the Sun.",
      "source": {
        "label": "NASA GSFC — Periodicity of Solar Eclipses",
        "url": "https://eclipse.gsfc.nasa.gov/SEsaros/SEperiodicity.html"
      },
      "tags": [
        "l02p1",
        "moon",
        "lunar-months",
        "derived"
      ],
      "uid": "br2s3l1divx2p"
    },
    {
      "id": "tfr-ast-d-synodic-month",
      "shape": "trueFalse",
      "derivedFrom": "ast-d-synodic-month",
      "statement": "Synodic month — the 29.53-day round trip from one new Moon to the next, timed against the Sun rather than against the background stars.",
      "isTrue": true,
      "why": "One body passing in front of a star, its starlight dimming in a pattern that maps structures far too faint to photograph, is an occultation. The synodic month is a stretch of time: the 29.53-day round trip from one new Moon to the next, timed against the Sun rather than the background stars.",
      "source": {
        "label": "NASA GSFC — Periodicity of Solar Eclipses",
        "url": "https://eclipse.gsfc.nasa.gov/SEsaros/SEperiodicity.html"
      },
      "tags": [
        "l02p1",
        "moon",
        "lunar-months",
        "derived"
      ],
      "uid": "we29bwusrqsa"
    },
    {
      "id": "ast-f-eclipse-umbra-strip",
      "shape": "fact",
      "title": "The Shadow's Narrow Strip",
      "body": "A shadow has two parts: an **umbra**, where the light is completely blocked, and a **penumbra**, where it is only partly blocked. In a solar eclipse the umbra lands on Earth as a narrow strip — the **path of totality**. Stand inside it and the eclipse is total; stand anywhere in the surrounding penumbra and it is partial. Totality is geography, not luck.",
      "factVariant": "image-heavy",
      "imageCaption": "Only the narrow track of the umbra sees totality; everyone around it sees a partial eclipse.",
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Moon umbral shadow on Earth photographed from orbit during a solar eclipse",
        "entityTerm": "Solar eclipse",
        "imagePrompt": "A photograph taken from orbit looking down at Earth during a total solar eclipse: a sharply darker circular umbral patch on the cloud tops, fading outward into a larger, softer penumbral shading.",
        "alt": "The Moon's dark umbral shadow sitting as a small round patch on Earth's cloud tops, photographed from orbit during a solar eclipse",
        "depictable": true,
        "credit": "Pexels · Zelch Csaba · Pexels License",
        "creditUrl": "https://www.pexels.com/photo/stunning-view-of-earth-during-solar-eclipse-30596283/",
        "subject": "A full daylit Earth viewed from orbit (Africa and Europe visible under white clouds) with a distinct black circular patch sitting over central/southern Africa — this is the Moon's umbral shadow on Earth's surface exactly as the card describes.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-eclipse-umbra-strip.webp"
      },
      "source": {
        "label": "USNO Astronomical Almanac Glossary — umbra",
        "url": "https://aa.usno.navy.mil/faq/asa_glossary"
      },
      "tags": [
        "l02p2",
        "eclipse",
        "shadow"
      ],
      "uid": "mat0z41hua5y6"
    },
    {
      "id": "ast-f-eclipse-totality-brief",
      "shape": "fact",
      "title": "Totality Never Lasts",
      "body": "A total solar eclipse gives between about **10 seconds and 7.5 minutes** of totality, and no more. The umbra sweeps across the ground at more than a thousand kilometres an hour, so no single spot stays inside it for long. The partial phases either side of it last hours; totality does not. Totality is the one and only phase that is safe to watch unfiltered — the moment the bright disc returns, the filter must be back on.",
      "source": {
        "label": "NASA — Eclipse Frequently Asked Questions",
        "url": "https://science.nasa.gov/eclipses/faq/"
      },
      "tags": [
        "l02p2",
        "eclipse",
        "duration"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "total solar eclipse totality white corona around a black lunar disc",
        "entityTerm": "Solar eclipse",
        "imagePrompt": "A photograph of totality in a total solar eclipse: a jet-black lunar disc ringed by the pearly white corona streaming outward, sky dark around it.",
        "alt": "A total solar eclipse at totality: the Moon's completely black disc centred in frame with the Sun's white corona streaming out around it in irregular rays, a faint pink chromospheric edge at the…",
        "depictable": true,
        "subject": "A total solar eclipse at totality: the Moon's completely black disc centred in frame with the Sun's white corona streaming out around it in irregular rays, a faint pink chromospheric edge at the lower limb, against a black sky.",
        "credit": "Pexels · Stunning image of total solar eclipse showing the sun's corona against a dark sky.",
        "creditUrl": "https://www.pexels.com/photo/total-lunar-eclipse-21298469/",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-eclipse-totality-brief.webp"
      },
      "uid": "10wxbmkns67ny"
    },
    {
      "id": "ast-f-eclipse-400-coincidence",
      "shape": "fact",
      "title": "Four Hundred by Four Hundred",
      "body": "The Sun's diameter is about **400 times** the Moon's — and the Sun happens to sit about **400 times** farther away. The two ratios cancel, so the discs look almost exactly the same size from Earth, which is why totality lasts minutes rather than hours, and why a Moon near apogee leaves a ring instead. Nothing in physics requires the match.",
      "source": {
        "label": "NASA — Total Solar Eclipse 2024: The Moon's Moment in the Sun",
        "url": "https://science.nasa.gov/solar-system/skywatching/eclipses/solar-eclipses/2024-solar-eclipse/total-solar-eclipse-2024-the-moons-moment-in-the-sun/"
      },
      "tags": [
        "l02p2",
        "eclipse",
        "coincidence"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "annular solar eclipse ring of fire photograph",
        "entityTerm": "Annular eclipse",
        "imagePrompt": "A photograph of an annular solar eclipse at maximum, an unbroken thin ring of brilliant sunlight surrounding the black lunar disc.",
        "alt": "An annular eclipse: a complete bright ring of sunlight left showing around the Moon when it is too far away to cover the Sun",
        "depictable": true,
        "credit": "Ken Lund from Reno, Nevada, USA · CC BY-SA 2.0",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:The_%22Ring_of_Fire%22_-_Annular_Solar_Eclipse,_Mesquite,_Nevada_(3)_(7239346576).jpg",
        "subject": "A complete, symmetric bright orange-gold ring of sunlight around a dark Moon on a black sky — the 'Ring of Fire' annular eclipse at Mesquite, Nevada (Wikimedia, CC BY-SA 2.0).",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-eclipse-400-coincidence.webp"
      },
      "uid": "1n0khpxq85931"
    },
    {
      "id": "ast-f-eclipse-saros-cycle",
      "shape": "fact",
      "title": "Predicted Without Computers",
      "body": "Two lunar clocks run at slightly different speeds: the synodic month of 29.530589 days, and the **draconic month** — node to node — of 27.212221 days. They come back into step after 223 synodic months, which is also 242 draconic months: the **saros**, about **6,585.3 days**, or 18 years, 11 days and 8 hours. Those extra 8 hours turn Earth a further **120 degrees**, so each repeat lands a third of the way around the planet.",
      "source": {
        "label": "NASA GSFC — Periodicity of Solar Eclipses",
        "url": "https://eclipse.gsfc.nasa.gov/SEsaros/SEperiodicity.html"
      },
      "tags": [
        "l02p2",
        "eclipse",
        "saros"
      ],
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "saros cycle eclipse repetition diagram 18 years 11 days one third around Earth",
        "imagePrompt": "Flat vector diagram: two rows of tick marks for the synodic and draconic months converging after 223 and 242 counts, beside a globe showing three successive eclipse tracks each shifted 120 degrees in longitude.",
        "alt": "A photograph of a total solar eclipse: the Moon's black disc with the Sun's white corona glowing around it and faint pink prominences at the lower-left limb, small in frame against a fully black sky.",
        "depictable": true,
        "allowGenerated": true,
        "subject": "A photograph of a total solar eclipse: the Moon's black disc with the Sun's white corona glowing around it and faint pink prominences at the lower-left limb, small in frame against a fully black sky.",
        "credit": "Pexels · Dramatic total solar eclipse with visible corona against a dark sky.",
        "creditUrl": "https://www.pexels.com/photo/total-eclipse-of-the-sun-23279637/",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-eclipse-saros-cycle.webp"
      },
      "uid": "g3y0rs1a2es9m"
    },
    {
      "id": "ast-d-penumbra",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Penumbra"
      },
      "definition": {
        "modality": "text",
        "value": "The outer part of a shadow, where the light source is partly blocked rather than hidden completely"
      },
      "curatedDistractors": [
        "Umbra",
        "Path of totality",
        "Annular eclipse"
      ],
      "source": {
        "label": "USNO Astronomical Almanac Glossary — umbra",
        "url": "https://aa.usno.navy.mil/faq/asa_glossary"
      },
      "tags": [
        "l02p2",
        "eclipse",
        "shadow"
      ],
      "uid": "deznqr1jvhmyx"
    },
    {
      "id": "ast-p-annular-eclipse",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Annular eclipse"
      },
      "sideB": {
        "modality": "text",
        "value": "A bright ring left uncovered by a too-distant Moon — never safe to view unfiltered",
        "short": "Ring left by a distant Moon"
      },
      "source": {
        "label": "NASA — Types of Solar Eclipses",
        "url": "https://science.nasa.gov/eclipses/types/"
      },
      "tags": [
        "l02p2",
        "eclipse",
        "annular"
      ],
      "uid": "1s11h1h1ucfwph"
    },
    {
      "id": "ast-p-iso-solar-filter",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "ISO 12312-2"
      },
      "sideB": {
        "modality": "text",
        "value": "The standard a safe solar filter has to meet"
      },
      "source": {
        "label": "NASA — Eclipse Safety",
        "url": "https://science.nasa.gov/eclipses/safety/"
      },
      "tags": [
        "l02p2",
        "eclipse",
        "safety"
      ],
      "uid": "27srf89kyjcq"
    },
    {
      "id": "ast-q-eclipse-solar-phase",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "A solar eclipse can only happen at which phase?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Waning crescent"
        },
        {
          "modality": "text",
          "value": "New Moon"
        },
        {
          "modality": "text",
          "value": "Full Moon"
        },
        {
          "modality": "text",
          "value": "First quarter"
        }
      ],
      "correctIndex": 1,
      "explanation": "The Moon has to pass between Earth and the Sun, and that is exactly what a new Moon is. A full Moon sits on the opposite side, so it can only give a lunar eclipse; at first quarter and waning crescent the three bodies are nowhere near a line.",
      "source": {
        "label": "NASA — Eclipses and the Moon",
        "url": "https://science.nasa.gov/moon/eclipses/"
      },
      "tags": [
        "l02p2",
        "eclipse",
        "phases"
      ],
      "uid": "a8bu921jf7z50"
    },
    {
      "id": "ast-q-eclipse-optics-filter",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Why is looking through binoculars while wearing eclipse glasses unsafe?"
      },
      "options": [
        {
          "modality": "text",
          "value": "They focus ultraviolet only"
        },
        {
          "modality": "text",
          "value": "They shift the light to infrared"
        },
        {
          "modality": "text",
          "value": "They polarise the incoming light"
        },
        {
          "modality": "text",
          "value": "They concentrate the sunlight"
        }
      ],
      "correctIndex": 3,
      "explanation": "Binoculars gather light over a wide front lens and bring it to a point — far more energy than the filter was designed to stop. They do not shift wavelength, polarise, or select ultraviolet; the filter must sit in FRONT of the optics, never behind it.",
      "source": {
        "label": "NASA — Eclipse Safety",
        "url": "https://science.nasa.gov/eclipses/safety/"
      },
      "tags": [
        "l02p2",
        "eclipse",
        "safety"
      ],
      "uid": "1cpvq6iufpo0a"
    },
    {
      "id": "czr-ast-d-penumbra",
      "shape": "cloze",
      "derivedFrom": "ast-d-penumbra",
      "template": "___ — The outer part of a shadow, where the light source is partly blocked rather than hidden completely",
      "answer": "Penumbra",
      "distractors": [
        "Coronal hole",
        "Exosphere",
        "Lithosphere"
      ],
      "explanation": "Penumbra is the outer part of a shadow, where the light source is partly blocked rather than hidden completely — not Coronal hole.",
      "source": {
        "label": "USNO Astronomical Almanac Glossary — umbra",
        "url": "https://aa.usno.navy.mil/faq/asa_glossary"
      },
      "tags": [
        "l02p2",
        "eclipse",
        "shadow",
        "derived"
      ],
      "uid": "luq5l6xubzg2"
    },
    {
      "id": "tfr-ast-d-penumbra",
      "shape": "trueFalse",
      "derivedFrom": "ast-d-penumbra",
      "statement": "Penumbra — the glowing head of gas and dust already driven off a comet.",
      "isTrue": false,
      "why": "A coma is the glowing head of gas and dust already driven off a comet, and it can swell wider than Jupiter as the nucleus warms. A penumbra belongs to shadows rather than comets: the outer part of a shadow, where the light source is partly blocked rather than hidden completely.",
      "source": {
        "label": "USNO Astronomical Almanac Glossary — umbra",
        "url": "https://aa.usno.navy.mil/faq/asa_glossary"
      },
      "tags": [
        "l02p2",
        "eclipse",
        "shadow",
        "derived"
      ],
      "whyOptions": [
        "Coma",
        "Coronal hole",
        "Exosphere"
      ],
      "whyCorrectIndex": 0,
      "uid": "orw8vy1fdu6s2"
    },
    {
      "id": "ast-f-earth-tilt-seasons",
      "shape": "fact",
      "title": "Sunlight at an Angle",
      "body": "Seasons come from **axial tilt**: Earth's rotation axis leans **23.4 degrees** away from the perpendicular to its orbital plane. That lean changes the angle at which sunlight strikes the ground and the length of the day, concentrating the same sunlight into a smaller area or spreading it thin. Its extremes are the **solstices**, the longest and shortest days — the extreme of sunlight, not of heat, which lags by weeks.",
      "factVariant": "image-heavy",
      "imageCaption": "The tilt changes the angle of the light and the length of the day — not the distance.",
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "Earth axial tilt seasons orbit diagram solstice equinox sunlight angle",
        "imagePrompt": "Flat vector diagram of Earth at solstices and equinoxes around the Sun, rotation axis leaning a constant 23.4 degrees, with an inset comparing sunlight spread over a large area versus concentrated on a small one.",
        "alt": "Diagram of Earth at four points around its orbit with the axis leaning a fixed 23.4 degrees, showing sunlight striking each hemisphere at different angles",
        "depictable": true,
        "allowGenerated": true
      },
      "source": {
        "label": "NASA — Earth Facts",
        "url": "https://science.nasa.gov/earth/facts/"
      },
      "tags": [
        "l02p3",
        "earth",
        "seasons"
      ],
      "uid": "1cfc52p1r3hylh"
    },
    {
      "id": "ast-f-summer-at-aphelion",
      "shape": "fact",
      "title": "Summer at Our Farthest",
      "body": "Earth reaches **aphelion**, its farthest point from the Sun, in early July — 6 July in 2026, at about **152.1 million km** — and perihelion, its closest, in early January. The Northern Hemisphere therefore has its summer at the moment Earth is farthest away. The whole swing is only about **3 percent** of the average distance: the orbit is very nearly circular, whatever school diagrams suggest.",
      "source": {
        "label": "USNO Astronomical Applications — Earth's Seasons and Apsides, 2026",
        "url": "https://aa.usno.navy.mil/calculated/seasons?year=2026&tz=0&tz_sign=-1&tz_label=false&dst=false&submit=Get+Data"
      },
      "tags": [
        "l02p3",
        "earth",
        "orbit"
      ],
      "uid": "7hm9smiqitey"
    },
    {
      "id": "ast-f-tides-two-bulges",
      "shape": "fact",
      "title": "Two Bulges, Not One",
      "body": "What raises a tide is the **difference** in the Moon's pull across the width of Earth, not the pull itself. The near side is pulled hardest and bulges toward the Moon; on the far side the pull is weakest, inertia wins, and the water bulges outward the other way. Earth turns through both, which is why coasts get **two** high and two low tides every 24 hours and 50 minutes.",
      "source": {
        "label": "NOAA National Ocean Service — Gravity, Inertia, and the Two Bulges",
        "url": "https://oceanservice.noaa.gov/education/tutorial_tides/tides03_gravity.html"
      },
      "tags": [
        "l02p3",
        "tides",
        "gravity"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Bay of Fundy low tide",
        "imagePrompt": "Documentary-style photograph: Boats resting on exposed mud at low tide in the Bay of Fundy, which has the world's most extreme tidal range. Natural light, no readable text, no logos, no watermarks.",
        "alt": "Boats resting on exposed mud at low tide in the Bay of Fundy, which has the world's most extreme tidal range"
      },
      "uid": "1iyfjbh1e9wv75"
    },
    {
      "id": "ast-f-moon-retreat-laser",
      "shape": "fact",
      "title": "Measured by Laser",
      "body": "**Lunar laser ranging** off the retroreflector arrays left by Apollo 11, 14 and 15 shows the Moon receding about **3.8 centimetres a year** — a direct measurement repeated for over fifty years, not an inference from theory. The same tidal friction is slowing Earth, lengthening the day by about **2.4 milliseconds per century**. What Earth's spin loses, the Moon's orbit gains.",
      "source": {
        "label": "NASA JPL — The Apollo Experiment That Keeps on Giving",
        "url": "https://www.jpl.nasa.gov/news/the-apollo-experiment-that-keeps-on-giving/"
      },
      "tags": [
        "l02p3",
        "moon",
        "tidal-friction"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Apollo lunar laser ranging retroreflector array on the surface of the Moon",
        "entityTerm": "Lunar Laser Ranging experiment",
        "imagePrompt": "A photograph of an Apollo lunar laser ranging retroreflector panel sitting on the grey lunar surface, its grid of corner-cube prisms catching the sunlight.",
        "alt": "The panel of corner-cube retroreflectors left on the lunar surface by an Apollo crew, still returning laser pulses",
        "depictable": true,
        "credit": "Wikipedia — Lunar Laser Ranging experiments · See Wikimedia Commons",
        "creditUrl": "https://en.wikipedia.org/wiki/Lunar_Laser_Ranging_experiments",
        "subject": "The actual Apollo 11 laser-ranging retroreflector panel (grid of corner-cube prisms) deployed and sitting on the lunar surface, with the Lunar Module and astronaut bootprints visible in the background -- this is exactly the object and setting the alt text describes.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-moon-retreat-laser.webp"
      },
      "uid": "19mj1zuh4zt9q"
    },
    {
      "id": "ast-d-equinox",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Equinox"
      },
      "definition": {
        "modality": "text",
        "value": "A point where the ecliptic crosses the celestial equator, with the axis leaning neither toward nor away from the Sun — the balance between the solstices, not an extreme"
      },
      "curatedDistractors": [
        "Solstice",
        "Perihelion",
        "Aphelion"
      ],
      "source": {
        "label": "USNO Astronomical Almanac Glossary — equinox",
        "url": "https://aa.usno.navy.mil/faq/asa_glossary"
      },
      "tags": [
        "l02p3",
        "earth",
        "seasons"
      ],
      "uid": "14815fm1oxe9ls"
    },
    {
      "id": "ast-p-spring-tide",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Spring tide"
      },
      "sideB": {
        "modality": "text",
        "value": "Extra-large water rise when Sun and Moon align"
      },
      "source": {
        "label": "NOAA National Ocean Service — Tidal Variations: the Influence of Position and Distance",
        "url": "https://oceanservice.noaa.gov/education/tutorial_tides/tides06_variations.html"
      },
      "tags": [
        "l02p3",
        "tides",
        "spring-neap"
      ],
      "uid": "pvholm12chyy0"
    },
    {
      "id": "ast-p-solar-retinopathy",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Solar retinopathy"
      },
      "sideB": {
        "modality": "text",
        "value": "Permanent eye damage from one unprotected look"
      },
      "source": {
        "label": "American Academy of Ophthalmology — Solar Eclipse Eye Safety",
        "url": "https://www.aao.org/eye-health/tips-prevention/solar-eclipse-eye-safety"
      },
      "tags": [
        "l02p3",
        "safety",
        "vision"
      ],
      "uid": "7f1jc4xe7hfe"
    },
    {
      "id": "ast-q-seasons-cause",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "What makes the Northern Hemisphere warm in July?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Its axis leans toward the Sun"
        },
        {
          "modality": "text",
          "value": "Earth is closest to the Sun"
        },
        {
          "modality": "text",
          "value": "The Sun gives out more light"
        },
        {
          "modality": "text",
          "value": "It climbs higher than in January"
        }
      ],
      "correctIndex": 0,
      "explanation": "Earth is farthest from the Sun in early July, so distance gets the sign backwards, and the Sun's output barely changes. Climbing higher IS what July does — but that is the tilt showing its effect, not a rival cause. The lean is the cause; the rest follows from it.",
      "source": {
        "label": "NASA — Earth Facts",
        "url": "https://science.nasa.gov/earth/facts/"
      },
      "tags": [
        "l02p3",
        "earth",
        "seasons"
      ],
      "uid": "1rbj9861nwq2lc"
    },
    {
      "id": "ast-q-tides-distance-cube",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Why does the Moon beat the far more massive Sun at raising tides?"
      },
      "options": [
        {
          "modality": "text",
          "value": "It falls off as distance cubed"
        },
        {
          "modality": "text",
          "value": "The Moon orbits us, not the Sun"
        },
        {
          "modality": "text",
          "value": "The Sun pulls on us more weakly"
        },
        {
          "modality": "text",
          "value": "Water answers the nearer body"
        }
      ],
      "correctIndex": 0,
      "explanation": "Tide-generating force depends on the difference in pull across Earth, and that difference drops as the cube of distance — so the Sun's huge mass loses to its huge distance and raises about half the tide. Its gravity is not weak, moonlight has no pull, and nothing is blocked.",
      "source": {
        "label": "NOAA National Ocean Service — What Causes Tides?",
        "url": "https://oceanservice.noaa.gov/education/tutorial_tides/tides02_cause.html"
      },
      "tags": [
        "l02p3",
        "tides",
        "distance"
      ],
      "uid": "1rekx6v1m5u8g3"
    },
    {
      "id": "czr-ast-d-equinox",
      "shape": "cloze",
      "derivedFrom": "ast-d-equinox",
      "template": "___ — A point where the ecliptic crosses the celestial equator, with the axis leaning neither toward nor away from the Sun — the balance between the solstices, not an extreme",
      "answer": "Equinox",
      "distractors": [
        "Synodic month",
        "Solar flare",
        "Sol"
      ],
      "explanation": "Equinox is a point where the ecliptic crosses the celestial equator, with the axis leaning neither toward nor away from the Sun. Synodic month, the closest of the alternatives, is the 29.53-day round trip from one new Moon to the next, timed against the Sun rather than against the background stars.",
      "source": {
        "label": "USNO Astronomical Almanac Glossary — equinox",
        "url": "https://aa.usno.navy.mil/faq/asa_glossary"
      },
      "tags": [
        "l02p3",
        "earth",
        "seasons",
        "derived"
      ],
      "uid": "1h3gdkx1qsph3p"
    },
    {
      "id": "tfr-ast-d-equinox",
      "shape": "trueFalse",
      "derivedFrom": "ast-d-equinox",
      "statement": "Equinox — a point where the ecliptic crosses the celestial equator, with the axis leaning neither toward nor away from the Sun.",
      "isTrue": true,
      "why": "An equinox is a point where the ecliptic crosses the celestial equator, with the axis leaning neither toward nor away from the Sun — day and night run near equal. A solar flare is a minutes-to-hours burst of electromagnetic radiation from the Sun's atmosphere, graded by X-ray flux.",
      "source": {
        "label": "USNO Astronomical Almanac Glossary — equinox",
        "url": "https://aa.usno.navy.mil/faq/asa_glossary"
      },
      "tags": [
        "l02p3",
        "earth",
        "seasons",
        "derived"
      ],
      "uid": "979wip373cnl"
    },
    {
      "id": "ast-f-sun-not-a-fire",
      "shape": "fact",
      "title": "Not a Fire, a Standoff",
      "body": "A star is not burning. Combustion is chemistry, and no chemical reaction could run the Sun for billions of years — it runs on **nuclear fusion**. Nor is it an explosion: the outward pressure of that fusion balances the inward pull of its own gravity almost exactly. That standoff is **hydrostatic equilibrium**, and it is what holds a main sequence star steady. Every later stage of a star's life is the balance being lost.",
      "source": {
        "label": "NASA/Webb — Star Lifecycle",
        "url": "https://science.nasa.gov/mission/webb/star-lifecycle/"
      },
      "tags": [
        "l03p1",
        "sun",
        "fusion"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "full solar disc photographed in white light showing a calm photosphere",
        "entityTerm": "Sun",
        "imagePrompt": "A white-light photograph of the entire solar disc, evenly bright with limb darkening toward the edge, against black space.",
        "alt": "The Sun's full disc in white light, a steady, sharply bounded sphere rather than anything resembling a flame",
        "depictable": true,
        "credit": "Unsplash · Foto Micha · Unsplash License",
        "creditUrl": "https://unsplash.com/photos/the-sun-with-dark-sunspots-against-black-background-PDzvs8sFIe8",
        "subject": "a full, sharply-bounded pale white/cream solar disc on black with several small dark sunspots scattered across an otherwise calm, evenly-lit face — a clean white-light photosphere image",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-sun-not-a-fire.webp"
      },
      "uid": "1wpcqtn4a87sn"
    },
    {
      "id": "ast-f-sun-ten-jupiters",
      "shape": "fact",
      "title": "Ten Jupiters Across",
      "body": "The Sun is about **1.4 million kilometres** wide — 109 Earths laid side by side, and roughly **ten times wider than Jupiter**. It would take about **330,000 Earths** to match its mass. The Sun is not a big planet; it is a different category of object, and its size is the first evidence.",
      "factVariant": "image-heavy",
      "imageCaption": "109 Earths would fit across the Sun — and Jupiter about ten times.",
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "Sun Jupiter and Earth diameter comparison to scale diagram",
        "imagePrompt": "Flat scale diagram: an arc of the Sun's disc filling the frame with Jupiter and Earth drawn to true relative size beside it, each labelled with its diameter.",
        "alt": "A six-panel rendered size-comparison chart of planets and stars (the Dave Jarvis-derived 'comparison of planets and stars, sheet by sheet' graphic from Wikimedia Commons).",
        "depictable": true,
        "allowGenerated": true,
        "subject": "A six-panel rendered size-comparison chart of planets and stars (the Dave Jarvis-derived 'comparison of planets and stars, sheet by sheet' graphic from Wikimedia Commons). Panel 3, labelled 'Jupiter < Wolf 359 < Sun < Sirius', shows Jupiter as a small sphere about a tenth of the Sun's width; panel 2",
        "credit": "Wikimedia Commons · Jcpag2012 and Dave Jarvis · CC BY-SA 4.0",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:Comparison_of_planets_and_stars_(sheet_by_sheet)_(Apr_2015_update).png",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-sun-ten-jupiters.webp"
      },
      "source": {
        "label": "NASA Science — Sun: Facts",
        "url": "https://science.nasa.gov/sun/facts/"
      },
      "tags": [
        "l03p1",
        "sun",
        "scale"
      ],
      "uid": "depzbo19wkbx0"
    },
    {
      "id": "ast-f-sun-pp-chain",
      "shape": "fact",
      "title": "Four Hydrogens, One Helium",
      "body": "Fusion in the Sun is a specific sequence, not one collision. In the **proton-proton chain**, four hydrogen nuclei end up as one helium-4 nucleus by way of deuterium and helium-3 — and the first step is the slow one. It dominates in cores around 15 million K and below, ours among them. The **CNO cycle** runs here too but supplies only about **one percent** of the output, a share the Borexino detector measured directly in 2020.",
      "source": {
        "label": "Lawrence Berkeley National Laboratory — Proton-Proton Chain",
        "url": "https://aether.lbl.gov/www/tour/elements/stellar/pp.html"
      },
      "tags": [
        "l03p1",
        "sun",
        "fusion"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Borexino neutrino detector Gran Sasso laboratory interior sphere",
        "entityTerm": "Borexino",
        "imagePrompt": "A photograph inside the Borexino detector at Gran Sasso: the large spherical vessel studded with photomultiplier tubes, seen from within.",
        "alt": "The interior of the Borexino neutrino detector, the instrument that measured how small the CNO cycle's share of the Sun's output is",
        "depictable": true,
        "credit": "Wikipedia — Borexino · See Wikimedia Commons",
        "creditUrl": "https://en.wikipedia.org/wiki/Borexino",
        "subject": "The Borexino detector's giant insulated stainless-steel sphere seen from a catwalk inside the underground hall at Laboratori Nazionali del Gran Sasso — the real detector, matching the Wikipedia 'Borexino' article's own lead image.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-sun-pp-chain.webp"
      },
      "uid": "1517iqn1uu3g4j"
    },
    {
      "id": "ast-f-sun-fusion-in-core",
      "shape": "fact",
      "title": "Fusion Only in the Core",
      "body": "From the middle outward the Sun is layered: **core**, **radiative zone**, **convective zone**, the visible **photosphere**, then an atmosphere of **chromosphere**, a thin transition region, and the **corona**. Fusion happens only in the core — the innermost **20 to 25 percent** of the radius. The Sun does not fuse hydrogen throughout its volume; everything outside the core is a delivery system.",
      "source": {
        "label": "NASA Science — The Sun Spot blog: Layers of the Sun",
        "url": "https://science.nasa.gov/blogs/the-sun-spot/2023/09/26/layers-of-the-sun/"
      },
      "tags": [
        "l03p1",
        "sun",
        "structure"
      ],
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "Sun interior cutaway diagram core radiative zone convective zone photosphere corona",
        "imagePrompt": "Flat vector cutaway of the Sun showing, from the centre out, core, radiative zone, convective zone, photosphere, chromosphere and corona, with the core shaded and labelled as the only region where fusion happens.",
        "alt": "Cutaway diagram of the Sun with fusion confined to the innermost quarter of the radius and every outer layer labelled",
        "depictable": true,
        "allowGenerated": true
      },
      "uid": "rekg081elr05o"
    },
    {
      "id": "ast-f-sun-half-done",
      "shape": "fact",
      "title": "Average, and Half Done",
      "body": "By class the Sun is a **G2 V** star: photosphere about 5,500 °C, core about 15 million °C, age about **4.6 billion years**. It is average for its class and outnumbered by dimmer stars. Roughly **5 billion years** of main sequence life remain, then about a billion as a red giant, ending as a white dwarf. Nothing about that is sudden — the Sun cannot go out or explode without warning.",
      "source": {
        "label": "NASA Science — Sun: Facts",
        "url": "https://science.nasa.gov/sun/facts/"
      },
      "tags": [
        "l03p1",
        "sun",
        "lifecycle"
      ],
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "life cycle of a Sun-like star diagram main sequence red giant white dwarf",
        "imagePrompt": "Flat vector timeline of a Sun-like star's life, marked at 4.6 billion years elapsed, with the remaining main sequence span, the red giant phase and the final white dwarf drawn to relative duration.",
        "alt": "Timeline diagram of a Sun-like star: about five billion years of main sequence still to run, then a red giant phase, then a white dwarf",
        "depictable": true,
        "allowGenerated": true
      },
      "uid": "2nxem91rvmy75"
    },
    {
      "id": "ast-p-sun-spectral-class",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Sun's spectral class"
      },
      "sideB": {
        "modality": "text",
        "value": "G2 V — a yellow dwarf, mid-range on the spectral sequence"
      },
      "source": {
        "label": "NASA Science — Sun: Facts",
        "url": "https://science.nasa.gov/sun/facts/"
      },
      "tags": [
        "l03p1",
        "sun",
        "classification"
      ],
      "uid": "8yne1v2mxr1f"
    },
    {
      "id": "ast-p-sun-composition",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "The Sun's ingredients"
      },
      "sideB": {
        "modality": "text",
        "value": "About three quarters hydrogen, one quarter helium — by mass"
      },
      "source": {
        "label": "Stanford Solar Center — The Sun's Vital Statistics",
        "url": "https://solar-center.stanford.edu/vitalstats"
      },
      "tags": [
        "l03p1",
        "sun",
        "composition"
      ],
      "uid": "4iu8ly1s3zige"
    },
    {
      "id": "ast-d-solar-mass",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Solar mass"
      },
      "definition": {
        "modality": "text",
        "value": "The Sun's own mass, about 1.99 × 10^30 kg, adopted as the yardstick every other star is quoted against — stellar masses are quoted in Suns, not in kilograms"
      },
      "source": {
        "label": "Stanford Solar Center — The Sun's Vital Statistics",
        "url": "https://solar-center.stanford.edu/vitalstats"
      },
      "tags": [
        "l03p1",
        "sun",
        "mass"
      ],
      "uid": "1lfoazlyah6pb"
    },
    {
      "id": "ast-q-sun-holds-itself-up",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "What holds a main sequence star up against its own gravity?"
      },
      "options": [
        {
          "modality": "text",
          "value": "The speed of its rotation"
        },
        {
          "modality": "text",
          "value": "Chemical burning of its fuel"
        },
        {
          "modality": "text",
          "value": "Outward pressure from fusion"
        },
        {
          "modality": "text",
          "value": "A dense solid core"
        }
      ],
      "correctIndex": 2,
      "explanation": "Combustion is chemistry — no chemical reaction could run a star for billions of years. Rotation does not support a star, and the Sun has no solid core: it is plasma throughout. Steadiness comes from fusion pressure balancing gravity almost exactly.",
      "source": {
        "label": "NASA/Webb — Star Lifecycle",
        "url": "https://science.nasa.gov/mission/webb/star-lifecycle/"
      },
      "tags": [
        "l03p1",
        "sun",
        "fusion"
      ],
      "uid": "1q4k1cofdpqbq"
    },
    {
      "id": "ast-q-sun-cno-share",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "How much of the Sun's energy output comes from the CNO cycle?"
      },
      "options": [
        {
          "modality": "text",
          "value": "About 40 percent"
        },
        {
          "modality": "text",
          "value": "About 15 percent"
        },
        {
          "modality": "text",
          "value": "About 1 percent"
        },
        {
          "modality": "text",
          "value": "About 99 percent"
        }
      ],
      "correctIndex": 2,
      "explanation": "Borexino measured the CNO share directly in 2020 and put it at order 1 percent; the proton-proton chain supplies the rest. The 99 percent option swaps the two routes, and 15 or 40 percent would need a core far hotter than 15 million K.",
      "source": {
        "label": "Borexino Collaboration (INFN Gran Sasso) — Nature press release on CNO neutrino detection",
        "url": "https://borex.lngs.infn.it/nature-cno-press-release/"
      },
      "tags": [
        "l03p1",
        "sun",
        "fusion"
      ],
      "uid": "ajrzlg3p9t8u"
    },
    {
      "id": "tfr-ast-d-solar-mass",
      "shape": "trueFalse",
      "derivedFrom": "ast-d-solar-mass",
      "statement": "Solar mass — how bright a thing looks from Earth, on a ranking inherited from Hipparchus.",
      "isTrue": false,
      "why": "Apparent magnitude is how bright a thing looks from Earth, on a ranking inherited from Hipparchus in which smaller numbers mean brighter objects. The solar mass is a unit of mass rather than of brightness: the Sun's own mass, about 1.99 × 10^30 kg, the yardstick every other star is quoted against.",
      "source": {
        "label": "Stanford Solar Center — The Sun's Vital Statistics",
        "url": "https://solar-center.stanford.edu/vitalstats"
      },
      "tags": [
        "l03p1",
        "sun",
        "mass",
        "derived"
      ],
      "whyOptions": [
        "Airmass",
        "Apparent magnitude",
        "Escape speed"
      ],
      "whyCorrectIndex": 1,
      "uid": "m8u7q4sqdwj4"
    },
    {
      "id": "ast-f-sun-slow-escape",
      "shape": "fact",
      "title": "A 170,000-Year Journey Out",
      "body": "Energy made in the core does not fly straight out. In the **radiative zone** it is absorbed and re-emitted so many times that reaching the top of the convection zone takes something like **170,000 years** — an order-of-magnitude estimate, since published figures vary widely, not a measurement. The light on your face was released before the last ice age ended, and only then crossed the final 150 million kilometres in eight minutes.",
      "source": {
        "label": "NASA Science — Sun: Facts",
        "url": "https://science.nasa.gov/sun/facts/"
      },
      "tags": [
        "l03p2",
        "sun",
        "energy-transport"
      ],
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "photon random walk through the Sun's radiative zone diagram",
        "imagePrompt": "Flat vector diagram of the Sun's interior with a tangled random-walk path from the core through the radiative zone to the convective zone, contrasted with a straight arrow showing the direct distance.",
        "alt": "Diagram of energy zig-zagging outward through the radiative zone by repeated absorption and re-emission rather than travelling straight out",
        "depictable": true,
        "allowGenerated": true
      },
      "uid": "1rthvrctefssc"
    },
    {
      "id": "ast-f-sun-granulation",
      "shape": "fact",
      "title": "A Pot at Rolling Boil",
      "body": "The outer **200,000 kilometres** of the solar interior carry heat by boiling rather than by radiation. **Granulation** is that boil seen from outside: bright cells of rising plasma about **1,500 km** across — roughly the width of Texas — each lasting **8 to 20 minutes**, with cooler plasma sinking in the dark lanes between them. The Sun's surface is not a still, uniform ball of light.",
      "factVariant": "image-heavy",
      "imageCaption": "Each bright cell is about 1,500 km across and lasts only minutes.",
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "solar granulation convection cells photosphere Inouye Solar Telescope",
        "entityTerm": "Granule (solar physics)",
        "imagePrompt": "A high-resolution photograph of the solar photosphere filling the frame with granulation: bright cell-shaped upwellings about 1,500 km across separated by narrow dark intergranular lanes.",
        "alt": "A high-resolution close-up of the Sun's photosphere showing solar granulation: a dense mosaic of irregular bright gold convection cells separated by thin dark lanes with small bright points in the…",
        "depictable": true,
        "subject": "A high-resolution close-up of the Sun's photosphere showing solar granulation: a dense mosaic of irregular bright gold convection cells separated by thin dark lanes with small bright points in the lanes. Consistent with the Daniel K. Inouye Solar Telescope first-light granulation image (NSF/NSO/AURA",
        "credit": "Wikimedia Commons · NSO/NSF/AURA · CC BY 4.0",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:NSF%E2%80%99s_Inouye_Solar_Telescope_First_Light_(NSO-DKIST-firstlight-full).jpg",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-sun-granulation.webp"
      },
      "source": {
        "label": "NASA Science — The Sun Spot blog: Layers of the Sun",
        "url": "https://science.nasa.gov/blogs/the-sun-spot/2023/09/26/layers-of-the-sun/"
      },
      "tags": [
        "l03p2",
        "sun",
        "convection"
      ],
      "uid": "1xtd32enx5oku"
    },
    {
      "id": "ast-f-sun-temperature-inversion",
      "shape": "fact",
      "title": "Hotter Farther From the Furnace",
      "body": "Through the **chromosphere**, only 3,000 to 5,000 km deep, temperature climbs outward from about **6,000 to about 20,000 degrees** — NASA's own pages give those numbers in °C on one and K on another. Higher still, NASA puts the **corona** at up to 2 million °C against a 5,500 °C surface, while ESA quotes around 1 million °C and calls it more than 150 times hotter. Move away from the furnace and it gets hundreds of times hotter. This is the **coronal heating problem**.",
      "source": {
        "label": "NASA Science — The Sun Spot blog: Layers of the Sun",
        "url": "https://science.nasa.gov/blogs/the-sun-spot/2023/09/26/layers-of-the-sun/"
      },
      "tags": [
        "l03p2",
        "sun",
        "temperature"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "solar corona extreme ultraviolet image Solar Dynamics Observatory AIA 171",
        "entityTerm": "Corona",
        "imagePrompt": "An extreme-ultraviolet image of the full Sun showing bright coronal loops arching above the limb, the hot corona clearly structured above the cooler surface.",
        "alt": "The million-degree corona in extreme ultraviolet, arching in loops far above a photosphere hundreds of times cooler",
        "depictable": true,
        "credit": "NASA's Scientific Visualization Studio - KBR Wyle Services, LLC/Scott Wiessinger · Public domain",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:Continuing_Strong_Solar_Flares-_May_15-16,_2024_(SVS14593_-_SDO_171_5-15-2024_0846UT).png",
        "subject": "A genuine SDO AIA 171 extreme-ultraviolet image of the full solar disk in gold during a strong May 2024 flare event, showing dramatic, clearly arched coronal loop arcades standing above the disk.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-sun-temperature-inversion.webp"
      },
      "uid": "gnfkhq8zid10"
    },
    {
      "id": "ast-f-coronal-heating-suspects",
      "shape": "fact",
      "title": "Two Suspects, No Verdict",
      "body": "The coronal heating problem is unsolved. Two mechanisms lead: **Alfvén waves** carrying magnetic energy outward from the interior, and **nanoflares**, small explosive releases of magnetic energy across the surface — with turbulence a related candidate ESA's Solar Orbiter is testing. Neither is settled and both may operate together. Recent missions narrowed the options rather than closing the question.",
      "source": {
        "label": "NASA — Parker Solar Probe and the curious case of the hot corona",
        "url": "https://www.nasa.gov/science-research/heliophysics/nasas-parker-solar-probe-and-the-curious-case-of-the-hot-corona"
      },
      "tags": [
        "l03p2",
        "sun",
        "open-question"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Solar Orbiter campfires extreme ultraviolet image of the solar corona",
        "entityTerm": "Solar Orbiter",
        "imagePrompt": "An extreme-ultraviolet image of a patch of the solar corona covered in small, scattered point-like brightenings against the darker background corona.",
        "alt": "Small-scale brightenings scattered across the corona in extreme ultraviolet — the nanoflare candidates for heating it",
        "depictable": true,
        "credit": "European Space Agency · CC BY-SA 3.0 igo",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:Solar_Orbiter%E2%80%99s_widest_high-res_view_of_the_Sun_ESA508430.jpg",
        "subject": "a genuine ESA/Solar Orbiter EUI extreme-ultraviolet mosaic of the full solar disc: golden/amber corona with dense filamentary structure, dark coronal-hole regions, and numerous small bright points scattered across the surface — no spacecraft in frame",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-coronal-heating-suspects.webp"
      },
      "uid": "1nvvmb26504ju"
    },
    {
      "id": "ast-f-maunder-minimum",
      "shape": "fact",
      "title": "The Decades Spots Vanished",
      "body": "Between about **1645 and 1715** sunspots nearly disappeared — the **Maunder Minimum**. Fewer than 50 were recorded in the 28 years from 1672 to 1699, against the 40,000 to 50,000 a comparable modern span would show. It fell inside the Little Ice Age, but the cooling had begun earlier and volcanism is thought the main cause, so that link is not settled. The 11-year cycle is a habit, not a law.",
      "source": {
        "label": "NOAA National Weather Service (Sioux Falls) — The Sun and Sunspots",
        "url": "https://www.weather.gov/fsd/sunspots"
      },
      "tags": [
        "l03p2",
        "sun",
        "solar-cycle"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "large sunspot group white light photograph solar photosphere",
        "entityTerm": "Sunspot",
        "imagePrompt": "A white-light close-up photograph of a large sunspot group showing dark umbrae and filamentary penumbrae against the granulated photosphere.",
        "alt": "The full disc of the Sun photographed in white light through a solar filter (peach-orange tint) against a black sky, with five or six sunspot groups scattered across the photosphere, each showing…",
        "depictable": true,
        "credit": "Pexels · Jay Brand · Pexels License",
        "creditUrl": "https://www.pexels.com/photo/detailed-sun-with-visible-sunspots-in-close-up-view-30286194/",
        "subject": "The full disc of the Sun photographed in white light through a solar filter (peach-orange tint) against a black sky, with five or six sunspot groups scattered across the photosphere, each showing dark umbrae ringed by lighter penumbrae, and visible limb darkening toward the edge.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-maunder-minimum.webp"
      },
      "uid": "15348wq1jf5s6w"
    },
    {
      "id": "ast-p-differential-rotation",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Differential rotation"
      },
      "sideB": {
        "modality": "text",
        "value": "25 days at the equator, about 36 at the poles"
      },
      "source": {
        "label": "NASA Science — Sun: Facts",
        "url": "https://science.nasa.gov/sun/facts/"
      },
      "tags": [
        "l03p2",
        "sun",
        "rotation"
      ],
      "uid": "gvuj8121kjvj"
    },
    {
      "id": "ast-p-sunspot-cycle-length",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Sunspot cycle length"
      },
      "sideB": {
        "modality": "text",
        "value": "About 11 years; polarity returns to where it began after 22"
      },
      "source": {
        "label": "NOAA Space Weather Prediction Center — Sunspots/Solar Cycle",
        "url": "https://www.spaceweather.gov/phenomena/sunspotssolar-cycle"
      },
      "tags": [
        "l03p2",
        "sun",
        "solar-cycle"
      ],
      "uid": "11tf9or1fd8wzf"
    },
    {
      "id": "ast-d-solar-flare",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Solar flare"
      },
      "definition": {
        "modality": "text",
        "value": "A minutes-to-hours burst of electromagnetic radiation from the Sun's atmosphere, graded by X-ray flux — light on its way to us, never matter"
      },
      "source": {
        "label": "NOAA Space Weather Prediction Center — Solar Flares (Radio Blackouts)",
        "url": "https://www.spaceweather.gov/phenomena/solar-flares-radio-blackouts"
      },
      "tags": [
        "l03p2",
        "sun",
        "flares"
      ],
      "uid": "esylnw10anekm"
    },
    {
      "id": "ast-q-sunspot-looks-dark",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Why does a sunspot look black?"
      },
      "options": [
        {
          "modality": "text",
          "value": "It is an object passing by"
        },
        {
          "modality": "text",
          "value": "It is cooler than the rest"
        },
        {
          "modality": "text",
          "value": "Its magnetism blocks the light"
        },
        {
          "modality": "text",
          "value": "It is a hole in the surface"
        }
      ],
      "correctIndex": 1,
      "explanation": "A sunspot sits near 3,482 °C against a 5,500 °C background, so alone it would still be dazzling. It is not a hole, and the Sun has no crust to cool — it is a patch where concentrated magnetism chokes off convection, and nothing passes in front.",
      "source": {
        "label": "NOAA National Weather Service (Sioux Falls) — The Sun and Sunspots",
        "url": "https://www.weather.gov/fsd/sunspots"
      },
      "tags": [
        "l03p2",
        "sun",
        "sunspots"
      ],
      "uid": "wlnydr16tzcyh"
    },
    {
      "id": "ast-q-flare-class-steps",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "An X1 flare is how much stronger than a C1 flare?"
      },
      "options": [
        {
          "modality": "text",
          "value": "5 times"
        },
        {
          "modality": "text",
          "value": "1,000 times"
        },
        {
          "modality": "text",
          "value": "100 times"
        },
        {
          "modality": "text",
          "value": "10 times"
        }
      ],
      "correctIndex": 2,
      "explanation": "Each letter is ten times the one below, so C to M is one factor of ten and M to X another — a hundred in all. Ten times is a single letter step, a thousand would need three, and five treats a logarithmic scale as if it were linear.",
      "source": {
        "label": "NOAA Space Weather Prediction Center — Solar Flares (Radio Blackouts)",
        "url": "https://www.spaceweather.gov/phenomena/solar-flares-radio-blackouts"
      },
      "tags": [
        "l03p2",
        "sun",
        "flares"
      ],
      "uid": "130orwm1asb9f8"
    },
    {
      "id": "czr-ast-d-solar-flare",
      "shape": "cloze",
      "derivedFrom": "ast-d-solar-flare",
      "template": "___ — A minutes-to-hours burst of electromagnetic radiation from the Sun's atmosphere, graded by X-ray flux — light on its way to us, never matter",
      "answer": "Solar flare",
      "distractors": [
        "Synodic month",
        "Equinox",
        "Sol"
      ],
      "explanation": "Solar flare is a minutes-to-hours burst of electromagnetic radiation from the Sun's atmosphere, graded by X-ray flux. Synodic month, the closest of the alternatives, is the 29.53-day round trip from one new Moon to the next, timed against the Sun rather than against the background stars.",
      "source": {
        "label": "NOAA Space Weather Prediction Center — Solar Flares (Radio Blackouts)",
        "url": "https://www.spaceweather.gov/phenomena/solar-flares-radio-blackouts"
      },
      "tags": [
        "l03p2",
        "sun",
        "flares",
        "derived"
      ],
      "uid": "gr53wrnbgd8f"
    },
    {
      "id": "tfr-ast-d-solar-flare",
      "shape": "trueFalse",
      "derivedFrom": "ast-d-solar-flare",
      "statement": "Solar flare — one body passing in front of a star, where the pattern of the starlight's dimming maps structures far too faint to photograph.",
      "isTrue": false,
      "why": "One body passing in front of a star, its starlight dimming in a pattern that maps structures far too faint to photograph, is an occultation. A solar flare is a minutes-to-hours burst of electromagnetic radiation from the Sun's atmosphere, graded by the X-ray flux it puts out.",
      "source": {
        "label": "NOAA Space Weather Prediction Center — Solar Flares (Radio Blackouts)",
        "url": "https://www.spaceweather.gov/phenomena/solar-flares-radio-blackouts"
      },
      "tags": [
        "l03p2",
        "sun",
        "flares",
        "derived"
      ],
      "whyOptions": [
        "Equinox",
        "Occultation",
        "Synodic month"
      ],
      "whyCorrectIndex": 1,
      "uid": "1c405wxxvcnap"
    },
    {
      "id": "ast-f-solar-wind-fills-space",
      "shape": "fact",
      "title": "Space Is Not Empty",
      "body": "The Sun is not sealed. Its corona escapes continuously as the **solar wind**, a plasma of protons and electrons. A slow stream of roughly **300 to 500 km/s** comes from coronal streamers near the equator; a fast stream of roughly **500 to 800 km/s** pours out of **coronal holes**, where the magnetic field opens to interplanetary space. Earth sits inside that outflow permanently, not only during storms.",
      "source": {
        "label": "NASA Scientific Visualization Studio — Fast and Slow Solar Wind",
        "url": "https://svs.gsfc.nasa.gov/20347/"
      },
      "tags": [
        "l03p3",
        "sun",
        "solar-wind"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "SOHO LASCO coronagraph image of coronal streamers around the occulted Sun",
        "entityTerm": "Solar and Heliospheric Observatory",
        "imagePrompt": "A coronagraph photograph: an occulting disc covers the Sun and the surrounding corona streams outward in long radial streamers against a starry field.",
        "alt": "A coronagraph image with the Sun's disc blocked out, showing the corona streaming continuously outward into space",
        "depictable": true,
        "credit": "SOHO (ESA &amp; NASA) · Public domain",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:Solar_maximum_coronal_streamers_from_SOHO_LASCO_C2.jpg",
        "subject": "A clean, public-domain SOHO LASCO C2 coronagraph image: the Sun's disc blacked out with a white ring marking the true photosphere size, and numerous bright coronal streamers radiating outward in all directions into a starfield — exactly the alt text's description",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-solar-wind-fills-space.webp"
      },
      "uid": "p79uw7zh8h5z"
    },
    {
      "id": "ast-f-aurora-own-light",
      "shape": "fact",
      "title": "Air Glowing on Its Own",
      "body": "An **aurora** is the visible end of the chain. Electrons accelerated in the tail of Earth's **magnetosphere** slam into oxygen and nitrogen **80 to 500 km** up and make them glow. This is atmospheric gas emitting its own light, not sunlight reflecting off anything. Earth's own magnetic field steers those electrons into two ovals centred on the magnetic poles, and in a strong storm the ovals push toward the equator.",
      "factVariant": "image-heavy",
      "imageCaption": "Oxygen and nitrogen 80 to 500 km up, emitting light of their own.",
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "aurora borealis green curtains over a dark landscape at night",
        "entityTerm": "Aurora",
        "imagePrompt": "A night photograph of green auroral curtains with vertical ray structure filling the sky above a dark, unlit landscape.",
        "alt": "A bright green auroral curtain arcing across a starry night sky, with fainter vertical rays to the right, above a black silhouetted mountain ridge.",
        "depictable": true,
        "credit": "Pexels · Bernd  Feurich · Pexels License",
        "creditUrl": "https://www.pexels.com/photo/bright-green-northern-lights-above-mountain-at-night-5474503/",
        "subject": "A bright green auroral curtain arcing across a starry night sky, with fainter vertical rays to the right, above a black silhouetted mountain ridge.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-aurora-own-light.webp"
      },
      "source": {
        "label": "NOAA Space Weather Prediction Center — Aurora",
        "url": "https://www.spaceweather.gov/phenomena/aurora"
      },
      "tags": [
        "l03p3",
        "sun",
        "aurora"
      ],
      "uid": "15d98drwtunu5"
    },
    {
      "id": "ast-f-carrington-event-1859",
      "shape": "fact",
      "title": "Telegraphs on Fire, 1859",
      "body": "On **1 September 1859** Richard Carrington and Richard Hodgson independently recorded the first solar flare ever observed. The coronal mass ejection behind it crossed to Earth in about **seventeen hours**; telegraph systems across Europe and North America failed, with operators reporting sparking equipment and fires, and aurorae were seen from Cuba, Hawaii and Colombia. The **Carrington Event** wrecked the only electrical network then in existence.",
      "source": {
        "label": "Wikipedia — Carrington Event",
        "url": "https://en.wikipedia.org/wiki/Carrington_Event"
      },
      "tags": [
        "l03p3",
        "sun",
        "space-weather"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Richard Carrington 1859 drawing of the solar flare and sunspot group",
        "entityTerm": "Carrington Event",
        "imagePrompt": "A scan of Richard Carrington's 1859 hand drawing of a complex sunspot group with the bright flare patches he observed marked on it.",
        "alt": "Carrington's own 1859 sketch of the sunspot group and the bright flare he saw cross it",
        "depictable": true,
        "credit": "Wikipedia — Carrington Event · See Wikimedia Commons",
        "creditUrl": "https://en.wikipedia.org/wiki/Carrington_Event",
        "subject": "An engraved scientific diagram of two overlapping sunspot groups with degree gridlines, a compass rose (N/S/P/F), and points labeled A, B, C, D — this is Carrington's own 1859 drawing of the sunspot group and the flare's path, filename 'Carrington_Richard_drawing_of_1859_sunspots.jpeg', hosted on th",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-carrington-event-1859.webp"
      },
      "uid": "5v1hdb1ldgjwp"
    },
    {
      "id": "ast-f-parker-inside-corona",
      "shape": "fact",
      "title": "Inside the Corona",
      "body": "**Parker Solar Probe** has flown within about **6.1 to 6.2 million km** of the Sun's surface at around 430,000 mph, which makes it the fastest object humans have built. NASA announced on **14 December 2021** that an earlier flyby, in April 2021 and far more distant, had already carried it through the corona itself and sampled the particles and magnetic fields there. Nothing melted: the corona is ferociously hot but extremely thin, and the pass is fast and brief.",
      "source": {
        "label": "NASA Science — Parker Solar Probe",
        "url": "https://science.nasa.gov/mission/parker-solar-probe/"
      },
      "tags": [
        "l03p3",
        "sun",
        "missions"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Parker Solar Probe spacecraft heat shield NASA",
        "entityTerm": "Parker Solar Probe",
        "imagePrompt": "A photograph of the Parker Solar Probe spacecraft in a clean room, its thick white heat shield facing the camera above the compact instrument bus.",
        "alt": "NASA's Parker Solar Probe spacecraft standing in a clean room at Goddard with its dark carbon-composite Thermal Protection System (heat shield) mounted on top, foil-wrapped instrument bus below…",
        "depictable": true,
        "credit": "NASA Goddard Space Flight Center · CC BY 2.0",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:Parker_Solar_Probe_Gets_Its_Revolutionary_Heat_Shield.jpg",
        "subject": "NASA's Parker Solar Probe spacecraft standing in a clean room at Goddard with its dark carbon-composite Thermal Protection System (heat shield) mounted on top, foil-wrapped instrument bus below, and a red mission decal on the side reading \"PARKER SOLAR PROBE — A MISSION TO TOUCH THE SUN\".",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-parker-inside-corona.webp"
      },
      "uid": "rmwjpalbyn6s"
    },
    {
      "id": "ast-p-cme-travel-time",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "How long a CME takes"
      },
      "sideB": {
        "modality": "text",
        "value": "15 to 18 hours if fast, several days if slow"
      },
      "source": {
        "label": "NOAA Space Weather Prediction Center — Coronal Mass Ejections",
        "url": "https://www.spaceweather.gov/phenomena/coronal-mass-ejections"
      },
      "tags": [
        "l03p3",
        "sun",
        "space-weather"
      ],
      "uid": "f97fet1tmfkkn"
    },
    {
      "id": "ast-p-g5-storm-grade",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "NOAA's top storm grade"
      },
      "sideB": {
        "modality": "text",
        "value": "G5 extreme — about four per 11-year cycle"
      },
      "source": {
        "label": "NOAA Space Weather Prediction Center — NOAA Space Weather Scales",
        "url": "https://www.spaceweather.gov/noaa-scales-explanation"
      },
      "tags": [
        "l03p3",
        "sun",
        "space-weather"
      ],
      "uid": "1l90hq6e777ss"
    },
    {
      "id": "ast-d-coronal-hole",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Coronal hole"
      },
      "definition": {
        "modality": "text",
        "value": "A region where the Sun's magnetic field opens to interplanetary space, letting plasma pour out at 500 to 800 km/s instead of the slower 300 to 500"
      },
      "source": {
        "label": "NASA Scientific Visualization Studio — Fast and Slow Solar Wind",
        "url": "https://svs.gsfc.nasa.gov/20347/"
      },
      "tags": [
        "l03p3",
        "sun",
        "solar-wind"
      ],
      "uid": "nfufw2xlta7q"
    },
    {
      "id": "ast-q-solar-viewing-safety",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Except during totality, what makes it safe to look at the Sun?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Binoculars used while wearing eclipse glasses",
          "short": "Binoculars + eclipse glasses"
        },
        {
          "modality": "text",
          "value": "A phone screen held up in front of your eyes",
          "short": "A phone screen held up"
        },
        {
          "modality": "text",
          "value": "Two pairs of sunglasses stacked together",
          "short": "Two stacked sunglasses"
        },
        {
          "modality": "text",
          "value": "Eclipse glasses that meet ISO 12312-2",
          "short": "ISO 12312-2 eclipse glasses"
        }
      ],
      "correctIndex": 3,
      "explanation": "Stacked sunglasses and a phone screen are not solar filters and block none of the damage. Binoculars concentrate the light and burn through the filter — it must sit in front of the optic, never behind it. Retinal injury is painless and untreatable.",
      "source": {
        "label": "NASA Science — Eclipse Safety",
        "url": "https://science.nasa.gov/eclipses/safety/"
      },
      "tags": [
        "l03p3",
        "sun",
        "safety"
      ],
      "uid": "n70yi7i9kx8v"
    },
    {
      "id": "ast-q-storm-hazard-target",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Geomagnetic storms drive currents through conductors. What is most at risk?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Car electronics"
        },
        {
          "modality": "text",
          "value": "Household wiring"
        },
        {
          "modality": "text",
          "value": "Continent-scale power grids"
        },
        {
          "modality": "text",
          "value": "Handheld radios"
        }
      ],
      "correctIndex": 2,
      "explanation": "The hazard is to long conductors: grids, pipelines, satellites, radio and GPS. A 1989 storm cut power to six million people in Quebec in 90 seconds. Bodies outdoors, aircraft structure and equatorial buildings are not what the induced currents couple into.",
      "source": {
        "label": "NOAA NESDIS — When Solar Storms Attack: Space Weather and our Infrastructure",
        "url": "https://www.nesdis.noaa.gov/news/when-solar-storms-attack-space-weather-and-our-infrastructure"
      },
      "tags": [
        "l03p3",
        "sun",
        "space-weather"
      ],
      "uid": "uc71gtong1up"
    },
    {
      "id": "czr-ast-d-coronal-hole",
      "shape": "cloze",
      "derivedFrom": "ast-d-coronal-hole",
      "template": "___ — A region where the Sun's magnetic field opens to interplanetary space, letting plasma pour out at 500 to 800 km/s instead of the slower 300 to 500",
      "answer": "Coronal hole",
      "distractors": [
        "Penumbra",
        "Exosphere",
        "Lithosphere"
      ],
      "explanation": "Coronal hole is a region where the Sun's magnetic field opens to interplanetary space, letting plasma pour out at 500 to 800 km/s instead of the slower 300 to 500 — not Penumbra.",
      "source": {
        "label": "NASA Scientific Visualization Studio — Fast and Slow Solar Wind",
        "url": "https://svs.gsfc.nasa.gov/20347/"
      },
      "tags": [
        "l03p3",
        "sun",
        "solar-wind",
        "derived"
      ],
      "uid": "1kokwbt166tyeb"
    },
    {
      "id": "tfr-ast-d-coronal-hole",
      "shape": "trueFalse",
      "derivedFrom": "ast-d-coronal-hole",
      "statement": "Coronal hole — the diagonal band of stars still fusing hydrogen in the core.",
      "isTrue": false,
      "why": "A coronal hole is a region where the Sun's magnetic field opens to interplanetary space, letting plasma pour out at 500 to 800 km/s instead of the slower 300 to 500. The main sequence is a feature of a star chart: the diagonal band of stars still fusing hydrogen in the core.",
      "source": {
        "label": "NASA Scientific Visualization Studio — Fast and Slow Solar Wind",
        "url": "https://svs.gsfc.nasa.gov/20347/"
      },
      "tags": [
        "l03p3",
        "sun",
        "solar-wind",
        "derived"
      ],
      "whyOptions": [
        "Exosphere",
        "Main sequence",
        "Penumbra"
      ],
      "whyCorrectIndex": 1,
      "uid": "1r9omb91vcobfl"
    },
    {
      "id": "ast-f-mercury-long-day",
      "shape": "fact",
      "title": "Mercury's 176-Day Day",
      "body": "Mercury turns exactly **three times** on its axis for every **two** trips around the Sun — a 3:2 spin-orbit resonance. One rotation takes 58.65 Earth days, but because the planet is also racing along its orbit, sunrise to sunrise takes **176 Earth days**. A day on Mercury lasts two of its years.",
      "factVariant": "image-heavy",
      "imageCaption": "Mercury's day is twice as long as its year.",
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "Mercury three to two spin orbit resonance diagram",
        "imagePrompt": "Flat vector diagram tracking a marked point on Mercury through two full orbits of the Sun and three axial rotations, with sunrise-to-sunrise spanning the whole 176-day sequence.",
        "alt": "Diagram of Mercury turning three times on its axis for every two orbits, so sunrise to sunrise takes two Mercury years",
        "depictable": true,
        "allowGenerated": true
      },
      "source": {
        "label": "ESO — Mercury: Length of Day and Year",
        "url": "https://www.eso.org/public/outreach/eduoff/vt-2004/mt-2003/mt-mercury-day.html"
      },
      "tags": [
        "l04p1",
        "mercury",
        "rotation"
      ],
      "uid": "12ezl6a1fcf6ds"
    },
    {
      "id": "ast-f-mercury-polar-ice",
      "shape": "fact",
      "title": "Ice Closest to the Sun",
      "body": "Mercury's spin axis is almost exactly upright, so the floors of deep polar craters **never see sunlight**. MESSENGER found those permanently shadowed floors hold **water ice** — on the same world whose sunlit surface reaches **430 °C**.",
      "factVariant": "image-heavy",
      "imageCaption": "The planet closest to the Sun keeps ice in craters the sunlight never reaches.",
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Mercury north polar permanently shadowed craters MESSENGER image",
        "entityTerm": "MESSENGER",
        "imagePrompt": "An orbital image of Mercury's north polar region, crater floors in permanent shadow shown dark against sunlit rims.",
        "alt": "A NASA MESSENGER polar-stereographic mosaic of Mercury's north polar region: grey cratered terrain with a latitude/longitude graticule, the dark permanently shadowed area around the pole, and…",
        "depictable": true,
        "credit": "NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of · Public domain",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:Radar-bright_Deposits_near_Mercury%27s_North_Pole_messenger_orbit_image20120322.jpg",
        "subject": "A NASA MESSENGER polar-stereographic mosaic of Mercury's north polar region: grey cratered terrain with a latitude/longitude graticule, the dark permanently shadowed area around the pole, and yellow patches marking the radar-bright (water-ice) deposits inside polar crater floors, including the large",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-mercury-polar-ice.webp"
      },
      "source": {
        "label": "NASA Science — Mercury: Facts",
        "url": "https://science.nasa.gov/mercury/facts/"
      },
      "tags": [
        "l04p1",
        "mercury",
        "ice"
      ],
      "uid": "15kwz2w1medajc"
    },
    {
      "id": "ast-f-mercury-metal-core",
      "shape": "fact",
      "title": "A Core Wearing a Planet",
      "body": "Mercury's iron core has a radius of about **2,074 km** inside a planet whose own radius is 2,439 km. The core reaches roughly **85 percent** of the way to the surface, leaving a rocky shell only a few hundred kilometres thick. By mass Mercury is about **70 percent metal** — proportionally far more than any other planet.",
      "source": {
        "label": "NASA Science — Mercury: Facts",
        "url": "https://science.nasa.gov/mercury/facts/"
      },
      "tags": [
        "l04p1",
        "mercury",
        "interior"
      ],
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "Mercury interior cutaway diagram oversized iron core thin rocky mantle",
        "imagePrompt": "Flat vector cutaway of Mercury drawn to scale: an enormous iron core of 2,074 km radius inside a planet of 2,439 km, leaving a narrow labelled mantle and crust.",
        "alt": "A rendered full-disc globe of the planet Mercury against a black starfield: a uniformly tan, heavily cratered surface with bright small rayed craters and no dark maria or atmosphere.",
        "depictable": true,
        "allowGenerated": true,
        "subject": "A rendered full-disc globe of the planet Mercury against a black starfield: a uniformly tan, heavily cratered surface with bright small rayed craters and no dark maria or atmosphere. It is a CGI stock render of the planet's exterior (Pexels, Zelch Csaba), not a cutaway of its interior and not a spac",
        "credit": "Pexels · Detailed view of Mercury, showcasing the planet's surface in outer space.",
        "creditUrl": "https://www.pexels.com/photo/planet-mercury-in-full-shot-photography-12498795/",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-mercury-metal-core.webp"
      },
      "uid": "z5u8kxugm5gj"
    },
    {
      "id": "ast-f-mercury-temp-swing",
      "shape": "fact",
      "title": "Six Hundred Degrees of Swing",
      "body": "Mercury's surface reaches about **430 °C** in daylight and falls to about **−180 °C** at night — a swing of roughly **610 °C**. Nothing holds the heat: Mercury has no atmosphere to move warmth around, so the night side becomes one of the coldest surfaces in the inner Solar System.",
      "source": {
        "label": "NASA Science — Mercury: Facts",
        "url": "https://science.nasa.gov/mercury/facts/"
      },
      "tags": [
        "l04p1",
        "mercury",
        "temperature"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Mercury full globe MESSENGER enhanced colour mosaic",
        "entityTerm": "Mercury (planet)",
        "imagePrompt": "A full-globe orbital mosaic of Mercury showing its heavily cratered, subtly colour-varied surface against black space.",
        "alt": "Mercury's full globe, an airless grey-brown world that swings six hundred degrees between day and night",
        "depictable": true,
        "credit": "Unsplash · NASA · Unsplash License",
        "creditUrl": "https://unsplash.com/photos/mercury-on-a-black-background-71W3CWeZF7A",
        "subject": "A grey, heavily cratered planetary crescent/gibbous globe on solid black, sharp terminator line, monochrome — attributed on Unsplash to 'Unsplash · NASA' with source title 'Mercury on a black background'; consistent with genuine spacecraft imagery of Mercury.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-mercury-temp-swing.webp"
      },
      "uid": "jaceh91f50309"
    },
    {
      "id": "ast-d-exosphere",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Exosphere"
      },
      "definition": {
        "modality": "text",
        "value": "The outermost gas of a world, so thin its atoms almost never collide — on Mercury it is knocked straight off the rock and never dense enough to be held"
      },
      "source": {
        "label": "NASA Science — Mercury: Facts",
        "url": "https://science.nasa.gov/mercury/facts/"
      },
      "tags": [
        "l04p1",
        "mercury",
        "atmosphere"
      ],
      "uid": "fzsuvgbvd2co"
    },
    {
      "id": "ast-p-caloris-basin",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Caloris Basin"
      },
      "sideB": {
        "modality": "text",
        "value": "A 1,550 km impact scar, a third of Mercury across",
        "short": "1,550 km impact scar"
      },
      "source": {
        "label": "NASA Science — Mercury: Facts",
        "url": "https://science.nasa.gov/mercury/facts/"
      },
      "tags": [
        "l04p1",
        "mercury",
        "surface"
      ],
      "uid": "4h0vte14yjka6"
    },
    {
      "id": "ast-p-mercury-year",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Mercury's year"
      },
      "sideB": {
        "modality": "text",
        "value": "88 Earth days — the shortest of any planet",
        "short": "88 Earth days"
      },
      "source": {
        "label": "NASA Science — Mercury: Facts",
        "url": "https://science.nasa.gov/mercury/facts/"
      },
      "tags": [
        "l04p1",
        "mercury",
        "orbit"
      ],
      "uid": "1lgmw5j1ij4285"
    },
    {
      "id": "ast-q-mercury-night-cold",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Why does Mercury's night side get so cold?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Its polar ice chills the ground"
        },
        {
          "modality": "text",
          "value": "It reflects most sunlight away"
        },
        {
          "modality": "text",
          "value": "It has no air to hold the heat"
        },
        {
          "modality": "text",
          "value": "Its core has frozen solid"
        }
      ],
      "correctIndex": 2,
      "explanation": "Mercury has no atmosphere to redistribute warmth. Its ice sits only in shadowed polar craters and warms nothing; its rotation is slow, not fast, at 58.65 days; and it is the closest planet to the Sun, not the farthest.",
      "source": {
        "label": "NASA Science — Mercury: Facts",
        "url": "https://science.nasa.gov/mercury/facts/"
      },
      "tags": [
        "l04p1",
        "mercury",
        "temperature"
      ],
      "uid": "aztsgt1xl56z9"
    },
    {
      "id": "ast-q-mercury-core-share",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "How far does Mercury's metal core reach toward the surface?"
      },
      "options": [
        {
          "modality": "text",
          "value": "About 30 percent of the way"
        },
        {
          "modality": "text",
          "value": "About 15 percent of the way"
        },
        {
          "modality": "text",
          "value": "About 85 percent of the way"
        },
        {
          "modality": "text",
          "value": "About 55 percent of the way"
        }
      ],
      "correctIndex": 2,
      "explanation": "The core's radius is 2,074 km inside a 2,439 km planet, leaving a rocky shell only a few hundred kilometres thick. Earth's core reaches roughly half way — the 55, 30 and 15 percent figures would all describe a far more ordinary rocky world.",
      "source": {
        "label": "NASA Science — Mercury: Facts",
        "url": "https://science.nasa.gov/mercury/facts/"
      },
      "tags": [
        "l04p1",
        "mercury",
        "interior"
      ],
      "uid": "15cmyi6mn7yhi"
    },
    {
      "id": "ast-q-mercury-gravity-twin",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Which planet pulls at almost exactly Mercury's surface gravity?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Neptune"
        },
        {
          "modality": "text",
          "value": "Mars"
        },
        {
          "modality": "text",
          "value": "Venus"
        },
        {
          "modality": "text",
          "value": "Earth"
        }
      ],
      "correctIndex": 1,
      "explanation": "Mercury pulls at 3.70 m/s² and Mars at 3.71 — nearly identical, even though Mars is almost 40 percent wider. Venus (8.87) and Earth (9.80) are more than twice as strong. Width alone does not set surface gravity; mass and radius together do.",
      "source": {
        "label": "JPL Solar System Dynamics — Planetary Physical Parameters",
        "url": "https://ssd.jpl.nasa.gov/planets/phys_par.html"
      },
      "tags": [
        "l04p1",
        "mercury",
        "gravity"
      ],
      "uid": "1ptjhqximzv0x"
    },
    {
      "id": "czr-ast-d-exosphere",
      "shape": "cloze",
      "derivedFrom": "ast-d-exosphere",
      "template": "___ — The outermost gas of a world, so thin its atoms almost never collide — on Mercury it is knocked straight off the rock and never dense enough to be held",
      "answer": "Exosphere",
      "distractors": [
        "Penumbra",
        "Coronal hole",
        "Lithosphere"
      ],
      "explanation": "Exosphere is the outermost gas of a world, so thin its atoms almost never collide. Penumbra, the closest of the alternatives, is the outer part of a shadow, where the light source is partly blocked rather than hidden completely.",
      "source": {
        "label": "NASA Science — Mercury: Facts",
        "url": "https://science.nasa.gov/mercury/facts/"
      },
      "tags": [
        "l04p1",
        "mercury",
        "atmosphere",
        "derived"
      ],
      "uid": "r8x41nkm801x"
    },
    {
      "id": "tfr-ast-d-exosphere",
      "shape": "trueFalse",
      "derivedFrom": "ast-d-exosphere",
      "statement": "Exosphere — the outermost gas of a world, so thin its atoms almost never collide.",
      "isTrue": true,
      "why": "The exosphere is the outermost gas of a world, so thin its atoms almost never collide but follow long ballistic arcs, the fastest of them leaving for good. The heliopause lies far beyond any of that: where the Sun's outflowing wind is finally halted by the gas between the stars.",
      "source": {
        "label": "NASA Science — Mercury: Facts",
        "url": "https://science.nasa.gov/mercury/facts/"
      },
      "tags": [
        "l04p1",
        "mercury",
        "atmosphere",
        "derived"
      ],
      "uid": "ohhg5kbf9mx6"
    },
    {
      "id": "ast-f-venus-backward-spin",
      "shape": "fact",
      "title": "Sunrise in the West",
      "body": "Venus turns once every **243 Earth days**, and it turns backwards — from the surface the Sun would rise in the west. Its year is only 225 Earth days, so one turn on its axis takes longer than one trip around the Sun. But sunrise to sunrise is just **117 Earth days**, half the rotation period: a backwards spin and a forward orbit add together instead of partly cancelling as they do on Earth.",
      "source": {
        "label": "NASA GISS — Climate Modeling Suggests Venus May Have Been Habitable",
        "url": "https://science.nasa.gov/earth/climate-change/nasa-climate-modeling-suggests-venus-may-have-been-habitable/"
      },
      "tags": [
        "l04p2",
        "venus",
        "rotation"
      ],
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "Venus retrograde rotation diagram Sun rising in the west",
        "imagePrompt": "Flat vector diagram of Venus orbiting the Sun with a rotation arrow pointing opposite to every other planet's, annotated with the 243-day spin, the 225-day year and the 117-day solar day.",
        "alt": "A near-full disk of the planet Venus — pale cream-yellow, shrouded in featureless cloud with faint darker streaks and a soft terminator on the right — small in the centre of a plain black…",
        "depictable": true,
        "allowGenerated": true,
        "subject": "A near-full disk of the planet Venus — pale cream-yellow, shrouded in featureless cloud with faint darker streaks and a soft terminator on the right — small in the centre of a plain black, starless background. A stock image (likely a render from a Venus cloud texture), not a diagram.",
        "credit": "Pexels · Image of planet Venus against a black space background, highlighting its atmospheric details.",
        "creditUrl": "https://www.pexels.com/photo/planet-in-space-darkness-20376411/",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-venus-backward-spin.webp"
      },
      "uid": "1l6ifdto2qjnn"
    },
    {
      "id": "ast-f-venus-lead-melting-surface",
      "shape": "fact",
      "title": "Lead Melts, Air Crushes",
      "body": "Venus's surface averages about **464 °C** — NASA's own figure is 467, so call it about 465 — hot enough to melt lead. That is a mean, not a noon peak: Venus is that hot day and night, pole to equator. The air above it presses down at about **92 times** Earth's sea-level pressure, comparable to being more than 900 metres underwater.",
      "source": {
        "label": "ESA — Venus's surface",
        "url": "https://www.esa.int/Science_Exploration/Space_Science/Venus_Express/Venus_s_surface"
      },
      "tags": [
        "l04p2",
        "venus",
        "temperature"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Venera 13 panorama Venus surface",
        "imagePrompt": "Documentary-style photograph: The rocky surface of Venus as photographed by the Venera 13 lander in 1982. Natural light, no readable text, no logos, no watermarks.",
        "alt": "The rocky surface of Venus as photographed by the Venera 13 lander in 1982"
      },
      "uid": "14tgugvb3ic4h"
    },
    {
      "id": "ast-f-venus-acid-cloud-deck",
      "shape": "fact",
      "title": "A Deck of Acid",
      "body": "Venus is the brightest planet in our sky, and the reason sits on top of it. Its **geometric albedo** is **0.65** — a measure of how brightly it shines back at us, not the share of sunlight it absorbs — against Mercury's **0.106**, bare rock about as dark as worn asphalt. The reflector is a deck of **sulphuric acid** droplets between about 45 and 70 km up.",
      "source": {
        "label": "JPL Solar System Dynamics — Planetary Physical Parameters",
        "url": "https://ssd.jpl.nasa.gov/planets/phys_par.html"
      },
      "tags": [
        "l04p2",
        "venus",
        "clouds"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Venus ultraviolet image of the sulphuric acid cloud deck Akatsuki",
        "entityTerm": "Venus",
        "imagePrompt": "An ultraviolet image of Venus's full disc revealing dark and bright banding within a completely closed, highly reflective cloud deck.",
        "alt": "A rendered (CGI, not spacecraft) visible-light view of Venus: a pale cream sphere wrapped in an unbroken deck of cloud with faint darker swirls, lit from the upper right against a black background.",
        "depictable": true,
        "subject": "A rendered (CGI, not spacecraft) visible-light view of Venus: a pale cream sphere wrapped in an unbroken deck of cloud with faint darker swirls, lit from the upper right against a black background. It is not an ultraviolet image.",
        "credit": "Pexels · Detailed view of the planet Venus with a dark cosmic background.",
        "creditUrl": "https://www.pexels.com/photo/planet-of-jupiter-20376409/",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-venus-acid-cloud-deck.webp"
      },
      "uid": "aluawh5li33x"
    },
    {
      "id": "ast-f-venus-radar-mapping",
      "shape": "fact",
      "title": "No Camera Can See It",
      "body": "The cloud deck is opaque, so no camera can photograph the ground. Venus's surface had to be mapped by **radar**, which passes straight through cloud and bounces off rock. NASA's **Magellan** orbiter flew synthetic-aperture radar from 1990 to 1994 and took coverage to **98 percent**. Every image you have seen of that surface is a radar map, not a photograph.",
      "factVariant": "image-heavy",
      "imageCaption": "Every view of the Venusian surface is a radar map, colour-coded — never a photograph.",
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Magellan synthetic aperture radar map of the surface of Venus",
        "entityTerm": "Magellan (spacecraft)",
        "imagePrompt": "A synthetic-aperture radar map of a region of Venus, ridges, volcanoes and lava plains rendered in radar brightness rather than visible light.",
        "alt": "A NASA/JPL Magellan synthetic-aperture radar image of Venus's surface (PIA00109), rendered as a computer-generated 3-D perspective view of the Idem-Kuva corona: ridged, fractured orange-brown…",
        "depictable": true,
        "credit": "NASA/JPL · Public domain",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:PIA00109_Venus_-_3-D_Perspective_View_of_Idem-Kuva.jpg",
        "subject": "A NASA/JPL Magellan synthetic-aperture radar image of Venus's surface (PIA00109), rendered as a computer-generated 3-D perspective view of the Idem-Kuva corona: ridged, fractured orange-brown terrain with a domed feature at centre under a black sky, with the false colour simulated from Venera lander",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-venus-radar-mapping.webp"
      },
      "source": {
        "label": "NASA Science — Magellan mission page",
        "url": "https://science.nasa.gov/mission/magellan/"
      },
      "tags": [
        "l04p2",
        "venus",
        "radar"
      ],
      "uid": "1g3jzb01y95uni"
    },
    {
      "id": "ast-p-venus-co2-inventory",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Carbon dioxide on Venus"
      },
      "sideB": {
        "modality": "text",
        "value": "About 154,000 times what Earth's air holds"
      },
      "source": {
        "label": "NASA Science — 10 Things: Planetary Atmospheres",
        "url": "https://science.nasa.gov/solar-system/10-things-planetary-atmospheres/"
      },
      "tags": [
        "l04p2",
        "venus",
        "atmosphere"
      ],
      "uid": "1q7klyi1xyx37o"
    },
    {
      "id": "ast-p-venus-surface-age",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Venus's surface age"
      },
      "sideB": {
        "modality": "text",
        "value": "Unsettled — estimates run 150 to 600 million years",
        "short": "150–600 million years"
      },
      "source": {
        "label": "NASA Science — Venus: Facts",
        "url": "https://science.nasa.gov/venus/venus-facts/"
      },
      "tags": [
        "l04p2",
        "venus",
        "geology"
      ],
      "uid": "198ld36ozfpps"
    },
    {
      "id": "ast-d-retrograde",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Retrograde"
      },
      "definition": {
        "modality": "text",
        "value": "Motion running opposite to the usual direction in a system — a backwards spin, which on Venus puts sunrise in the west"
      },
      "source": {
        "label": "JPL Solar System Dynamics — Planetary Physical Parameters",
        "url": "https://ssd.jpl.nasa.gov/planets/phys_par.html"
      },
      "tags": [
        "l04p2",
        "venus",
        "rotation"
      ],
      "uid": "1gv9557g8h96p"
    },
    {
      "id": "ast-q-venus-brightest-planet",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Why does Venus outshine every other planet?"
      },
      "options": [
        {
          "modality": "text",
          "value": "It sits nearest the Sun of all"
        },
        {
          "modality": "text",
          "value": "It glows from its own heat"
        },
        {
          "modality": "text",
          "value": "Its clouds bounce back sunlight"
        },
        {
          "modality": "text",
          "value": "It is the largest planet we see"
        }
      ],
      "correctIndex": 2,
      "explanation": "Mercury sits closest to the Sun and reflects barely a tenth of the light falling on it. Venus is indeed the hottest planet and it does spin backwards, but neither heat nor spin sends light back. Its acid cloud deck returns two-thirds of it — albedo 0.65.",
      "source": {
        "label": "JPL Solar System Dynamics — Planetary Physical Parameters",
        "url": "https://ssd.jpl.nasa.gov/planets/phys_par.html"
      },
      "tags": [
        "l04p2",
        "venus",
        "albedo"
      ],
      "uid": "1fmp92jgxhrap"
    },
    {
      "id": "ast-q-venera-lander-survival",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Why did the Venera landers stop working so quickly?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Heat and pressure destroyed them"
        },
        {
          "modality": "text",
          "value": "Acid dissolved their cameras"
        },
        {
          "modality": "text",
          "value": "Their batteries were undersized"
        },
        {
          "modality": "text",
          "value": "They sank into soft ground"
        }
      ],
      "correctIndex": 0,
      "explanation": "Ten probes reached the surface; the shortest lasted 23 minutes and the longest about two hours — Venera 13 managed 127 minutes against a 32-minute design life. At 464 °C and 92 atmospheres, days, weeks and months are out of reach for armoured hardware.",
      "source": {
        "label": "NASA Science — Venus: Facts",
        "url": "https://science.nasa.gov/venus/venus-facts/"
      },
      "tags": [
        "l04p2",
        "venus",
        "landers"
      ],
      "uid": "b4khs1w6shlq"
    },
    {
      "id": "ast-q-venus-dominant-gas",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Which gas makes up most of Venus's atmosphere?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Sulphur dioxide"
        },
        {
          "modality": "text",
          "value": "Methane"
        },
        {
          "modality": "text",
          "value": "Ammonia"
        },
        {
          "modality": "text",
          "value": "Carbon dioxide"
        }
      ],
      "correctIndex": 3,
      "explanation": "It is the same gas that drives Earth's greenhouse effect — Venus simply holds about 154,000 times more of it. Methane and ammonia are not what fills that air, and sulphur dioxide is not either: Venus's sulphur shows up as acid droplets in cloud, 45 to 70 km up.",
      "source": {
        "label": "NASA Science — 10 Things: Planetary Atmospheres",
        "url": "https://science.nasa.gov/solar-system/10-things-planetary-atmospheres/"
      },
      "tags": [
        "l04p2",
        "venus",
        "atmosphere"
      ],
      "uid": "1qgx0ydb8ygw3"
    },
    {
      "id": "czr-ast-d-retrograde",
      "shape": "cloze",
      "derivedFrom": "ast-d-retrograde",
      "template": "___ — Motion running opposite to the usual direction in a system — a backwards spin, which on Venus puts sunrise in the west",
      "answer": "Retrograde",
      "distractors": [
        "Runaway greenhouse",
        "Tidal heating",
        "Differentiated"
      ],
      "explanation": "Retrograde is motion running opposite to the usual direction in a system. Runaway greenhouse, the closest of the alternatives, is a greenhouse effect that feeds itself.",
      "source": {
        "label": "JPL Solar System Dynamics — Planetary Physical Parameters",
        "url": "https://ssd.jpl.nasa.gov/planets/phys_par.html"
      },
      "tags": [
        "l04p2",
        "venus",
        "rotation",
        "derived"
      ],
      "uid": "gha0761wezuhe"
    },
    {
      "id": "tfr-ast-d-retrograde",
      "shape": "trueFalse",
      "derivedFrom": "ast-d-retrograde",
      "statement": "Retrograde — warmth made inside a body by the flexing of a stretched orbit, rather than by sunlight or by radioactive decay.",
      "isTrue": false,
      "why": "Retrograde is motion running opposite to the usual direction in a system — Venus spins that way, and Triton orbits that way. Tidal heating names a source of warmth rather than a direction: heat made inside a body by the flexing of a stretched orbit, not by sunlight.",
      "source": {
        "label": "JPL Solar System Dynamics — Planetary Physical Parameters",
        "url": "https://ssd.jpl.nasa.gov/planets/phys_par.html"
      },
      "tags": [
        "l04p2",
        "venus",
        "rotation",
        "derived"
      ],
      "whyOptions": [
        "Differentiated",
        "Runaway greenhouse",
        "Tidal heating"
      ],
      "whyCorrectIndex": 2,
      "uid": "16koopb1wg5obv"
    },
    {
      "id": "ast-f-escape-velocity-ladder",
      "shape": "fact",
      "title": "The Speed to Get Out",
      "body": "**Escape velocity** — also called escape speed — is the speed something needs to leave a planet for good: **11.19 km/s** at Earth, **10.36 km/s** at Venus, 5.03 km/s at Mars and **4.25 km/s** at Mercury. It does not depend on what is trying to escape — a hydrogen atom and a rocket face the same number. Mass and radius set it, and nothing else does.",
      "source": {
        "label": "JPL Solar System Dynamics — Planetary Physical Parameters",
        "url": "https://ssd.jpl.nasa.gov/planets/phys_par.html"
      },
      "tags": [
        "l04p3",
        "escape-velocity",
        "comparison"
      ],
      "uid": "1un14hu1sdv4gm"
    },
    {
      "id": "ast-f-mercury-never-held-air",
      "shape": "fact",
      "title": "Never Had a Chance",
      "body": "Mercury loses the escape race twice over. It has the **lowest escape velocity** of the four rocky planets at **4.25 km/s**, and its dayside reaches about **430 °C** — and heat is molecular motion, so its gas moves fastest exactly where the grip is weakest. Weak gravity with a hot surface is the worst combination available. The solar wind did not blow Mercury's atmosphere away; Mercury could never hold one.",
      "source": {
        "label": "Catling & Kasting — Atmospheric Evolution, Ch. 5",
        "url": "https://sseh.uchicago.edu/doc/Catling_and_Kasting_ch_5.pdf"
      },
      "tags": [
        "l04p3",
        "mercury",
        "atmosphere-loss"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Mercury MESSENGER mosaic",
        "imagePrompt": "Documentary-style photograph: Mercury's cratered surface as photographed and mosaicked by NASA's MESSENGER spacecraft. Natural light, no readable text, no logos, no watermarks.",
        "alt": "Mercury's cratered surface as photographed and mosaicked by NASA's MESSENGER spacecraft",
        "credit": "Wikipedia — Mercury (planet) · See Wikimedia Commons",
        "creditUrl": "https://en.wikipedia.org/wiki/Mercury_(planet)",
        "subject": "A full-disc photographic mosaic of Mercury: a heavily cratered, gray-tan sphere with bright rayed craters, set against black space — consistent with the well-known MESSENGER-derived 'Mercury in true color' global mosaic.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-mercury-never-held-air.webp"
      },
      "uid": "1daknrp1h6bft"
    },
    {
      "id": "ast-f-venus-water-left-first",
      "shape": "fact",
      "title": "Water Left First",
      "body": "Sunlight evaporated Venus's surface water. **Ultraviolet** light broke the water molecules apart. **Hydrogen**, the lightest thing there is, escaped to space. And with no liquid water left to lock carbon into rock, carbon dioxide piled up with nothing to remove it — a **runaway greenhouse**. Read the chain in that order: losing the water is what disabled Venus's ability to bury its own carbon, which is why Venus is hotter than Mercury while orbiting nearly twice as far from the Sun.",
      "factVariant": "image-heavy",
      "imageCaption": "The water goes first; the carbon dioxide can only build up afterwards.",
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "runaway greenhouse water loss on Venus diagram ultraviolet hydrogen escape",
        "imagePrompt": "Flat vector flow diagram with four linked stages — surface water evaporating, ultraviolet photons splitting water molecules, hydrogen escaping to space, and carbon dioxide accumulating with no liquid water left to lock it into rock.",
        "alt": "Diagram of the chain on Venus: water evaporates, ultraviolet light splits it, hydrogen escapes, and carbon dioxide then has nothing to bury it",
        "depictable": true,
        "allowGenerated": true
      },
      "source": {
        "label": "NASA GISS — Climate Modeling Suggests Venus May Have Been Habitable",
        "url": "https://science.nasa.gov/earth/climate-change/nasa-climate-modeling-suggests-venus-may-have-been-habitable/"
      },
      "tags": [
        "l04p3",
        "venus",
        "runaway-greenhouse"
      ],
      "uid": "efreeh1uxzegp"
    },
    {
      "id": "ast-f-magnetic-field-no-shield",
      "shape": "fact",
      "title": "A Field Is No Shield",
      "body": "A global magnetic field is neither necessary nor sufficient for keeping an atmosphere. Venus has no internally generated field at all — only an **induced magnetic field** — and holds **92 atmospheres** of air. Mercury does have a global field, at about **1 percent** of Earth's surface strength, and holds essentially nothing. Escape speed and temperature are the levers here.",
      "source": {
        "label": "NASA Science — Venus: Facts",
        "url": "https://science.nasa.gov/venus/venus-facts/"
      },
      "tags": [
        "l04p3",
        "magnetic-field",
        "atmosphere"
      ],
      "uid": "18ssny1j6r452"
    },
    {
      "id": "ast-p-venus-early-ocean-model",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Venus's early ocean"
      },
      "sideB": {
        "modality": "text",
        "value": "Modelled, not observed — up to 2 billion habitable years",
        "short": "Modelled: up to 2 billion years"
      },
      "source": {
        "label": "NASA GISS — Climate Modeling Suggests Venus May Have Been Habitable",
        "url": "https://science.nasa.gov/earth/climate-change/nasa-climate-modeling-suggests-venus-may-have-been-habitable/"
      },
      "tags": [
        "l04p3",
        "venus",
        "habitability"
      ],
      "uid": "13j2bboteg92u"
    },
    {
      "id": "ast-p-planets-without-moons",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Planets with no moon"
      },
      "sideB": {
        "modality": "text",
        "value": "Mercury and Venus — alone among the eight"
      },
      "source": {
        "label": "NASA Science — Mercury: Facts",
        "url": "https://science.nasa.gov/mercury/facts/"
      },
      "tags": [
        "l04p3",
        "mercury",
        "venus"
      ],
      "uid": "jz7j5xj9jhjh"
    },
    {
      "id": "ast-d-runaway-greenhouse",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Runaway greenhouse"
      },
      "definition": {
        "modality": "text",
        "value": "A greenhouse effect that feeds itself: warming drives water into the air, the vapour traps more heat, and the ocean is lost — taking with it the rain that would have buried carbon in rock"
      },
      "source": {
        "label": "NASA GISS — Climate Modeling Suggests Venus May Have Been Habitable",
        "url": "https://science.nasa.gov/earth/climate-change/nasa-climate-modeling-suggests-venus-may-have-been-habitable/"
      },
      "tags": [
        "l04p3",
        "venus",
        "runaway-greenhouse"
      ],
      "uid": "z68rw11dh5w1h"
    },
    {
      "id": "ast-q-venus-collapse-order",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "What had to happen before carbon dioxide could pile up on Venus?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Its magnetic field had to die"
        },
        {
          "modality": "text",
          "value": "Its water had to be lost"
        },
        {
          "modality": "text",
          "value": "Its spin had to slow down"
        },
        {
          "modality": "text",
          "value": "Its clouds had to thicken first"
        }
      ],
      "correctIndex": 1,
      "explanation": "Sunlight evaporated the surface water, ultraviolet split the molecules and hydrogen escaped; only then, with nothing left to lock carbon into rock, did the gas accumulate. Venus has no internal field to lose, has never had a moon, and its slow spin is not part of the chain.",
      "source": {
        "label": "NASA GISS — Climate Modeling Suggests Venus May Have Been Habitable",
        "url": "https://science.nasa.gov/earth/climate-change/nasa-climate-modeling-suggests-venus-may-have-been-habitable/"
      },
      "tags": [
        "l04p3",
        "venus",
        "runaway-greenhouse"
      ],
      "uid": "17n8r8l13g7ghf"
    },
    {
      "id": "ast-q-atmosphere-retention-levers",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "What sets the basic physical limit on whether a planet can hold an atmosphere?"
      },
      "options": [
        {
          "modality": "text",
          "value": "A global magnetic field"
        },
        {
          "modality": "text",
          "value": "Escape speed and temperature"
        },
        {
          "modality": "text",
          "value": "The length of its year"
        },
        {
          "modality": "text",
          "value": "The number of moons"
        }
      ],
      "correctIndex": 1,
      "explanation": "Venus has no internal magnetic field and holds 92 atmospheres; Mercury has a field and holds nothing. Moons are no guide either — neither planet has any. Year length does not enter it: mass and radius fix the speed needed to leave, and heat drives molecules to reach it.",
      "source": {
        "label": "NASA Science — Venus: Facts",
        "url": "https://science.nasa.gov/venus/venus-facts/"
      },
      "tags": [
        "l04p3",
        "atmosphere",
        "magnetic-field"
      ],
      "uid": "g295t8152wis2"
    },
    {
      "id": "ast-q-lowest-escape-speed",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Which rocky planet is easiest to leave for good?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Mars"
        },
        {
          "modality": "text",
          "value": "Mercury"
        },
        {
          "modality": "text",
          "value": "Venus"
        },
        {
          "modality": "text",
          "value": "Earth"
        }
      ],
      "correctIndex": 1,
      "explanation": "Mercury needs only 4.25 km/s, the lowest of the four. Mars asks 5.03, Venus 10.36 and Earth 11.19 — Venus is nearly as hard to get away from as Earth. The figure does not depend on what is escaping; a planet's mass and radius fix it.",
      "source": {
        "label": "JPL Solar System Dynamics — Planetary Physical Parameters",
        "url": "https://ssd.jpl.nasa.gov/planets/phys_par.html"
      },
      "tags": [
        "l04p3",
        "escape-velocity",
        "mercury"
      ],
      "uid": "1ayp01y18sv96a"
    },
    {
      "id": "tfr-ast-d-runaway-greenhouse",
      "shape": "trueFalse",
      "derivedFrom": "ast-d-runaway-greenhouse",
      "statement": "Runaway greenhouse — a greenhouse effect that feeds itself.",
      "isTrue": true,
      "why": "Retrograde is motion running opposite to the usual direction in a system. A runaway greenhouse is a climate process rather than a motion: a greenhouse effect that feeds itself, warming driving more vapour into the air and the vapour trapping more heat, a loop that never settles.",
      "source": {
        "label": "NASA GISS — Climate Modeling Suggests Venus May Have Been Habitable",
        "url": "https://science.nasa.gov/earth/climate-change/nasa-climate-modeling-suggests-venus-may-have-been-habitable/"
      },
      "tags": [
        "l04p3",
        "venus",
        "runaway-greenhouse",
        "derived"
      ],
      "uid": "9z2hx290u4e4"
    },
    {
      "id": "ast-f-earth-moving-plates",
      "shape": "fact",
      "title": "The Only Crust That Moves",
      "body": "Earth's **lithosphere** — crust plus upper mantle — is broken into plates that constantly shift, with new crust made at ocean ridges and old crust carried back down at **subduction zones**. The USGS states that Earth is the only planetary body in the Solar System exhibiting **plate tectonics** in action. Venus's crust, by contrast, is all one piece, with no evidence of subduction. Drifting continents are not standard equipment on a rocky planet.",
      "factVariant": "image-heavy",
      "imageCaption": "Every other rocky world wears one unbroken shell of rock.",
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "plate tectonics cross-section diagram mid-ocean ridge and subduction zone",
        "imagePrompt": "Flat vector cross-section of Earth's outer layers showing a spreading mid-ocean ridge on one side and a subducting slab descending into the mantle on the other, both labelled.",
        "alt": "A labelled cross-section diagram of plate tectonics (German labels): on the left, ocean crust dives beneath continental crust at a subduction zone (\"Subduktionszone\") with melting and a volcano…",
        "depictable": true,
        "credit": "Wikimedia Commons · Hannes Grobe/AWI · CC BY-SA 4.0",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:Plattentektonik-profil_hg.png",
        "subject": "A labelled cross-section diagram of plate tectonics (German labels): on the left, ocean crust dives beneath continental crust at a subduction zone (\"Subduktionszone\") with melting and a volcano erupting above; on the right, a mid-ocean ridge (\"Mittelozeanischer Rücken\") where magma rises and arrows ",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-earth-moving-plates.webp"
      },
      "source": {
        "label": "USGS — This Dynamic Planet: Using the Diagram to Discuss How Plate Tectonics Works",
        "url": "https://volcanoes.usgs.gov/about/edu/dynamicplanet/nutshell.php"
      },
      "tags": [
        "l05p1",
        "earth",
        "tectonics"
      ],
      "uid": "fxhkkn6la06t"
    },
    {
      "id": "ast-f-earth-oxygen-from-life",
      "shape": "fact",
      "title": "Air Made by Life",
      "body": "Earth's air is **78 percent nitrogen**, **21 percent oxygen** and about 1 percent everything else — the only rocky-planet atmosphere that is not mostly carbon dioxide. The oxygen is not left over from formation: NASA states plainly that plants continuously produce it by **photosynthesis**. Before the **Great Oxidation Event**, roughly 2.4 billion years ago, the atmosphere was oxygen-poor.",
      "source": {
        "label": "NASA Science — Oxygen on Exoplanets Isn't Proof of Life",
        "url": "https://science.nasa.gov/universe/exoplanets/oxygen-on-exoplanets-isnt-proof-of-life/"
      },
      "tags": [
        "l05p1",
        "earth",
        "atmosphere"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "stromatolites living microbial mats Shark Bay Western Australia",
        "entityTerm": "Stromatolite",
        "imagePrompt": "A photograph of living stromatolites: dark, cushion-shaped microbial mounds standing in clear shallow salt water under bright daylight.",
        "alt": "Living stromatolites in shallow water — the kind of microbial mat whose photosynthesis put oxygen into Earth's air",
        "depictable": true,
        "credit": "Wikipedia — Hamelin Pool Marine Nature Reserve · See Wikimedia Commons",
        "creditUrl": "https://en.wikipedia.org/wiki/Hamelin_Pool_Marine_Nature_Reserve",
        "subject": "A broad shoreline view of numerous dark, rounded living stromatolite mounds emerging from shallow, clear turquoise water under open sky -- Hamelin Pool, Shark Bay",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-earth-oxygen-from-life.webp"
      },
      "uid": "nst0df19zdnkv"
    },
    {
      "id": "ast-f-earth-carbon-thermostat",
      "shape": "fact",
      "title": "Rain Files Carbon Into Rock",
      "body": "Liquid water covers **71 percent** of Earth's surface, and that water runs a thermostat. In the **slow carbon cycle**, warmth brings more rain, rain carrying **carbonic acid** dissolves rock faster, and the products bury carbon on the ocean floor — a self-correcting loop. NASA notes that with no greenhouse gases Earth would be a frozen **−18 °C**, and with too many it would be like Venus. The greenhouse effect is not a fault; the question is how much.",
      "source": {
        "label": "NASA Earth Observatory — The Carbon Cycle",
        "url": "https://science.nasa.gov/earth/earth-observatory/the-carbon-cycle/"
      },
      "tags": [
        "l05p1",
        "earth",
        "carbon-cycle"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "White Cliffs of Dover chalk carbonate cliffs",
        "entityTerm": "White Cliffs of Dover",
        "imagePrompt": "A photograph of tall white chalk sea cliffs rising from a shoreline, the horizontal bedding of the carbonate rock clearly visible.",
        "alt": "Tall white chalk cliffs rising into haze above a grassy shelf and a still pond at their foot, on the Kent coast near Dover (the Wikimedia title names the White Cliffs of Dover;",
        "depictable": true,
        "credit": "Wikimedia Commons · Keven Law from Los Angeles, USA · CC BY-SA 2.0",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:Flickr_-_law_keven_-_There%27ll_Be_Blue_Birds_Over_the_White_Cliffs_of_Dover....jpg",
        "subject": "Tall white chalk cliffs rising into haze above a grassy shelf and a still pond at their foot, on the Kent coast near Dover (the Wikimedia title names the White Cliffs of Dover; the reclaimed platform and pond match Samphire Hoe below Shakespeare Cliff). A small script signature \"© Keven Law ~ June 8",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-earth-carbon-thermostat.webp"
      },
      "uid": "4hsgyfj627i5"
    },
    {
      "id": "ast-f-earth-oversized-moon",
      "shape": "fact",
      "title": "A Moon Too Big",
      "body": "The Moon's radius is **1,738 km** — more than a quarter of Earth's width, and the **fifth largest** moon in the Solar System after Ganymede, Titan, Callisto and Io. Earth is also the only planet with exactly one moon; among the rocky worlds it is that single enormous moon that is the anomaly, since Mercury and Venus have none. It is widely held to steady Earth's tilt inside a narrow **22.1 to 24.5 degree** band, though how strong that effect really is remains debated.",
      "factVariant": "image-heavy",
      "imageCaption": "One moon looks ordinary until you notice how large this one is.",
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Earth and the Moon photographed together in a single frame from space",
        "entityTerm": "Moon",
        "imagePrompt": "A single spacecraft photograph containing both Earth and the Moon at their true relative sizes and separation, against black space.",
        "alt": "A to-scale 3D render of Earth (Africa, Europe, Arabia and India visible in NASA Blue Marble texture) beside the Moon (near-side maria visible), both lit from the upper left on a plain grey…",
        "depictable": true,
        "credit": "Wikimedia Commons · Lsmpascal · see source",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:Earth_moon_size_comparison.jpg",
        "subject": "A to-scale 3D render of Earth (Africa, Europe, Arabia and India visible in NASA Blue Marble texture) beside the Moon (near-side maria visible), both lit from the upper left on a plain grey backdrop with drop shadows; the Moon spans roughly 0.29 of Earth's width.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-earth-oversized-moon.webp"
      },
      "source": {
        "label": "NASA Science — Earth: Facts",
        "url": "https://science.nasa.gov/earth/facts/"
      },
      "tags": [
        "l05p1",
        "earth",
        "moon"
      ],
      "uid": "iogcypyojnaj"
    },
    {
      "id": "ast-p-earth-sidereal-day",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Sidereal day"
      },
      "sideB": {
        "modality": "text",
        "value": "23 h 56 m 04 s — one turn against the stars"
      },
      "source": {
        "label": "NASA Imagine the Universe (GSFC) — Ask an Astrophysicist: Earth",
        "url": "https://imagine.gsfc.nasa.gov/ask_astro/earth.html"
      },
      "tags": [
        "l05p1",
        "earth",
        "rotation"
      ],
      "uid": "64shuv1k85wub"
    },
    {
      "id": "ast-p-earth-global-ocean",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Earth's global ocean"
      },
      "sideB": {
        "modality": "text",
        "value": "71 percent of the surface, averaging 3.6 km deep",
        "short": "71% of the surface, 3.6 km deep"
      },
      "source": {
        "label": "NASA Science — Earth: Facts",
        "url": "https://science.nasa.gov/earth/facts/"
      },
      "tags": [
        "l05p1",
        "earth",
        "ocean"
      ],
      "uid": "1bm5gay7wziwe"
    },
    {
      "id": "ast-d-lithosphere",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Lithosphere"
      },
      "definition": {
        "modality": "text",
        "value": "The crust plus the rigid uppermost mantle taken together — the rigid outer shell that is divided into moving plates, not the crust alone"
      },
      "source": {
        "label": "USGS — This Dynamic Planet: Using the Diagram to Discuss How Plate Tectonics Works",
        "url": "https://volcanoes.usgs.gov/about/edu/dynamicplanet/nutshell.php"
      },
      "tags": [
        "l05p1",
        "earth",
        "tectonics"
      ],
      "uid": "im3q4ks8ejtm"
    },
    {
      "id": "ast-q-earth-oxygen-source",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Why is a fifth of the air you breathe oxygen?"
      },
      "options": [
        {
          "modality": "text",
          "value": "It was there from the start"
        },
        {
          "modality": "text",
          "value": "Sunlight splits it from ice"
        },
        {
          "modality": "text",
          "value": "Plants keep making it"
        },
        {
          "modality": "text",
          "value": "Volcanoes vent it from rock"
        }
      ],
      "correctIndex": 2,
      "explanation": "NASA states the oxygen is there because plants continuously produce it by photosynthesis. Before the Great Oxidation Event about 2.4 billion years ago the atmosphere was oxygen-poor, so it was not there from the start — and NASA names plants, not volcanoes or sunlight on ice.",
      "source": {
        "label": "NASA Science — Oxygen on Exoplanets Isn't Proof of Life",
        "url": "https://science.nasa.gov/universe/exoplanets/oxygen-on-exoplanets-isnt-proof-of-life/"
      },
      "tags": [
        "l05p1",
        "earth",
        "atmosphere"
      ],
      "uid": "d44ij3yjrc71"
    },
    {
      "id": "ast-q-earth-plate-tectonics",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Earth alone still runs plate tectonics. What does it do to the crust?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Holds it fixed against erosion"
        },
        {
          "modality": "text",
          "value": "Melts it away from below"
        },
        {
          "modality": "text",
          "value": "Slowly thickens it everywhere"
        },
        {
          "modality": "text",
          "value": "Makes new crust and recycles old"
        }
      ],
      "correctIndex": 3,
      "explanation": "New crust is made at ocean ridges and old crust is carried back into the mantle at subduction zones, so the surface is continually replaced rather than accumulated. That recycling is why Earth keeps so few very old rocks — and why the oldest surfaces in the Solar System are on worlds without it.",
      "source": {
        "label": "USGS — This Dynamic Planet: Using the Diagram to Discuss How Plate Tectonics Works",
        "url": "https://volcanoes.usgs.gov/about/edu/dynamicplanet/nutshell.php"
      },
      "tags": [
        "l05p1",
        "earth",
        "tectonics"
      ],
      "uid": "yhwdi5obtlrt"
    },
    {
      "id": "ast-q-earth-carbon-weathering",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "In Earth's slow carbon cycle, what does extra rain do?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Warms the deep ocean"
        },
        {
          "modality": "text",
          "value": "Traps more heat in the air"
        },
        {
          "modality": "text",
          "value": "Thickens the cloud deck"
        },
        {
          "modality": "text",
          "value": "Dissolves rock faster"
        }
      ],
      "correctIndex": 3,
      "explanation": "Warmth brings more rain, rain carrying carbonic acid dissolves rock faster, and the products bury carbon on the ocean floor. The loop removes carbon rather than releasing it, and NASA's account turns on weathering — not on a warming deep ocean or a thicker cloud deck.",
      "source": {
        "label": "NASA Earth Observatory — The Carbon Cycle",
        "url": "https://science.nasa.gov/earth/earth-observatory/the-carbon-cycle/"
      },
      "tags": [
        "l05p1",
        "earth",
        "carbon-cycle"
      ],
      "uid": "41axt1mxk4pd"
    },
    {
      "id": "czr-ast-d-lithosphere",
      "shape": "cloze",
      "derivedFrom": "ast-d-lithosphere",
      "template": "___ — The crust plus the rigid uppermost mantle taken together — the rigid outer shell that is divided into moving plates, not the crust alone",
      "answer": "Lithosphere",
      "distractors": [
        "Penumbra",
        "Coronal hole",
        "Exosphere"
      ],
      "explanation": "Lithosphere is the crust plus the rigid uppermost mantle taken together. Penumbra, the closest of the alternatives, is the outer part of a shadow, where the light source is partly blocked rather than hidden completely.",
      "source": {
        "label": "USGS — This Dynamic Planet: Using the Diagram to Discuss How Plate Tectonics Works",
        "url": "https://volcanoes.usgs.gov/about/edu/dynamicplanet/nutshell.php"
      },
      "tags": [
        "l05p1",
        "earth",
        "tectonics",
        "derived"
      ],
      "uid": "1o2j06rsjjg7v"
    },
    {
      "id": "tfr-ast-d-lithosphere",
      "shape": "trueFalse",
      "derivedFrom": "ast-d-lithosphere",
      "statement": "Lithosphere — the crust plus the rigid uppermost mantle taken together.",
      "isTrue": true,
      "why": "The lithosphere is the crust plus the rigid uppermost mantle taken together — the outer shell that cracks into plates, marked out by how the rock behaves rather than by what it is made of. A penumbra is a shadow term: the outer part of a shadow, where the light source is partly blocked.",
      "source": {
        "label": "USGS — This Dynamic Planet: Using the Diagram to Discuss How Plate Tectonics Works",
        "url": "https://volcanoes.usgs.gov/about/edu/dynamicplanet/nutshell.php"
      },
      "tags": [
        "l05p1",
        "earth",
        "tectonics",
        "derived"
      ],
      "uid": "1xj8qtmid6dwc"
    },
    {
      "id": "ast-f-mars-sol-clock",
      "shape": "fact",
      "title": "Mars Keeps Earth's Clock",
      "body": "A Martian solar day — a **sol** — lasts **24 hours 39 minutes 35 seconds**, only about **3 percent** longer than a day on Earth, which is why rover teams can live on Mars time. Its axis is tilted about **25 degrees**, near enough Earth's 23.4 to give it the same kind of seasons. Of everything that makes Mars uninhabitable, the length of the day is not on the list.",
      "source": {
        "label": "NASA GISS — Mars24 Sunclock: Technical Notes on Mars Solar Time",
        "url": "https://www.giss.nasa.gov/tools/mars24/help/notes.html"
      },
      "tags": [
        "l05p2",
        "mars",
        "rotation"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Curiosity rover self-portrait on the Martian surface",
        "entityTerm": "Curiosity (rover)",
        "imagePrompt": "A rover self-portrait on Mars: the vehicle in the foreground on rusty regolith with layered terrain and a pale butterscotch sky behind.",
        "alt": "The planet Mars as a full globe against black space, lit from the right, with the Valles Marineris canyon system running across its face — a rendered orbital view of the planet's real surface…",
        "depictable": true,
        "subject": "The planet Mars as a full globe against black space, lit from the right, with the Valles Marineris canyon system running across its face — a rendered orbital view of the planet's real surface features; no rover or ground-level scene is in frame.",
        "credit": "Pexels · A high-resolution image capturing Mars with its surface details visible in space.",
        "creditUrl": "https://www.pexels.com/photo/planet-in-cosmos-20337601/",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-mars-sol-clock.webp"
      },
      "uid": "1kcxpl21t31uze"
    },
    {
      "id": "ast-f-mars-olympus-mons",
      "shape": "fact",
      "title": "The Volcano That Never Moved",
      "body": "**Olympus Mons** is the largest volcano in the Solar System, more than **600 km** across at its base — the one figure the sources agree on. Its height is genuinely disputed: ESA gives about 22 km above the surrounding plains, one NASA page says 27 km, and NASA's Mars facts page says more than 40 km base to summit. The base has no clean edge. The mechanism is the durable part: with no plate tectonics the crust never slid off the hot spot, so eruptions piled up in one place.",
      "factVariant": "image-heavy",
      "imageCaption": "A mountain that grew because the ground under it never moved.",
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Olympus Mons shield volcano Mars orbiter view",
        "entityTerm": "Olympus Mons",
        "imagePrompt": "An orbital view of Olympus Mons showing the whole shield, its stepped basal escarpment and the nested calderas at the summit.",
        "alt": "Oblique orbital view (ESA Mars Express HRSC) of Olympus Mons on Mars: a broad tan shield volcano with a nested multi-pit summit caldera complex at its centre, a cliff-like basal escarpment along…",
        "depictable": true,
        "credit": "Wikipedia — Olympus Mons · See Wikimedia Commons",
        "creditUrl": "https://en.wikipedia.org/wiki/Olympus_Mons",
        "subject": "Oblique orbital view (ESA Mars Express HRSC) of Olympus Mons on Mars: a broad tan shield volcano with a nested multi-pit summit caldera complex at its centre, a cliff-like basal escarpment along its left and lower-left flank, and aureole terrain on the surrounding plains.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-mars-olympus-mons.webp"
      },
      "source": {
        "label": "NASA Science Photojournal — Olympus Mons",
        "url": "https://science.nasa.gov/photojournal/olympus-mons/"
      },
      "tags": [
        "l05p2",
        "mars",
        "volcano"
      ],
      "uid": "fsphbzl11u1n"
    },
    {
      "id": "ast-f-mars-valles-marineris",
      "shape": "fact",
      "title": "A Rift, Not a River",
      "body": "**Valles Marineris** is the largest canyon in the Solar System: about **3,870 km** long, up to 600 km across at its widest and **9.3 km** deep from rim to floor. It is not a river canyon like the Grand Canyon. It is chiefly a **tectonic rift** — crust pulled apart — later widened by landslides and water. Mars has a tenth of Earth's mass and still carries the biggest scar, because nothing ever came along to erase it.",
      "factVariant": "image-heavy",
      "imageCaption": "Long enough to reach across a continent, and nine kilometres deep.",
      "illustration": {
        "kind": "map",
        "imageSearchTerm": "Valles Marineris canyon system Viking global mosaic of Mars",
        "entityTerm": "Valles Marineris",
        "imagePrompt": "A global mosaic of Mars centred so that the Valles Marineris rift system runs as a dark gash across the middle of the disc, Tharsis volcanoes visible to the west.",
        "alt": "The full disk of Mars in the Viking 1 Orbiter global colour mosaic, with the Valles Marineris canyon system running horizontally across the equator for nearly the width of the planet;",
        "depictable": true,
        "subject": "The full disk of Mars in the Viking 1 Orbiter global colour mosaic, with the Valles Marineris canyon system running horizontally across the equator for nearly the width of the planet; Noctis Labyrinthus at its western end, chaos terrain and outflow channels at its eastern end, and the three Tharsis ",
        "credit": "Wikimedia Commons · NASA/USGS · Public domain",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:Mars_globe.jpg",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-mars-valles-marineris.webp"
      },
      "source": {
        "label": "NASA Science — Valles Marineris: The Grand Canyon of Mars",
        "url": "https://science.nasa.gov/resource/valles-marineris-the-grand-canyon-of-mars/"
      },
      "tags": [
        "l05p2",
        "mars",
        "canyon"
      ],
      "uid": "1et4k3213du18a"
    },
    {
      "id": "ast-f-mars-water-evidence",
      "shape": "fact",
      "title": "Three Kinds of Evidence",
      "body": "The case that Mars was once wet rests on three independent kinds of evidence. **Outflow channels** such as Ares Vallis were cut by catastrophic floods of released groundwater. **Jezero Crater** holds a delta and lakebed, filled more than **3.5 billion years** ago when river channels spilled over its rim. And **grey crystalline hematite** covers up to 20 percent of the surface at Meridiani Planum — a mineral that on Earth forms mostly in the presence of liquid water. Landforms, sediments and minerals all point the same way.",
      "source": {
        "label": "NASA Science Photojournal — Ares Valles",
        "url": "https://science.nasa.gov/photojournal/ares-valles/"
      },
      "tags": [
        "l05p2",
        "mars",
        "water"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Jezero Crater delta Mars Reconnaissance Orbiter view ancient river deposit",
        "entityTerm": "Jezero (crater)",
        "imagePrompt": "An orbital image of Jezero Crater's western delta: a layered, fan-shaped sedimentary deposit with a scalloped erosional front, inside the crater rim.",
        "alt": "The fan-shaped delta inside Jezero Crater, built where a river once spilled into a standing lake",
        "depictable": true,
        "credit": "NASA/JPL-Caltech/University of Arizona/USGS/JHU-APL",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:PIA24922-Mars-PerseveranceRover-RouteToDelta-20220915.jpg",
        "subject": "NASA/JPL orbital image of Jezero Crater with the fan-shaped delta and crater floor explicitly labeled 'Delta' and 'Crater Floor', plus the Perseverance rover's traverse route marked — exactly the ancient river delta the card describes",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-mars-water-evidence.webp"
      },
      "uid": "tjmmyo19191vq"
    },
    {
      "id": "ast-f-mars-temperature-range",
      "shape": "fact",
      "title": "Twenty Degrees, Then Lethal",
      "body": "Mars reaches about **20 °C** at its warmest and falls to about **−153 °C** at its coldest. NASA pages put the average between about **−53 and −63 °C** — they disagree, so carry the range rather than a single figure. It is not uniformly frozen; it is a world that can be shirtsleeve-warm at noon and lethal hours later, because the air is far too thin to move heat around or store it.",
      "source": {
        "label": "NASA Science — Mars: Facts",
        "url": "https://science.nasa.gov/mars/facts/"
      },
      "tags": [
        "l05p2",
        "mars",
        "temperature"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "water frost on the Martian surface at the Viking 2 lander site",
        "entityTerm": "Viking 2",
        "imagePrompt": "A surface photograph from a Mars lander in winter: a delicate white frost coating the rocks and soil of a boulder-strewn plain under a pale sky.",
        "alt": "The planet Mars as a full gibbous disc against black space, lit from the right: rust-orange surface with a small white north polar cap at the top, the dark horizontal gash of Valles Marineris just…",
        "depictable": true,
        "subject": "The planet Mars as a full gibbous disc against black space, lit from the right: rust-orange surface with a small white north polar cap at the top, the dark horizontal gash of Valles Marineris just below the equator on the left, and darker albedo markings across the right and lower hemisphere. No lan",
        "credit": "Pexels · Detailed view of Mars showcasing its surface features against a dark sky backdrop.",
        "creditUrl": "https://www.pexels.com/photo/moon-in-eclipse-20337600/",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-mars-temperature-range.webp"
      },
      "uid": "79o3a25klst2"
    },
    {
      "id": "ast-p-phobos-moon",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Phobos"
      },
      "sideB": {
        "modality": "text",
        "value": "27 by 22 by 18 km, three laps of Mars a day"
      },
      "source": {
        "label": "NASA Science — Phobos",
        "url": "https://science.nasa.gov/mars/moons/phobos/"
      },
      "tags": [
        "l05p2",
        "mars",
        "moons"
      ],
      "uid": "3mz8nur49uto"
    },
    {
      "id": "ast-p-deimos-moon",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Deimos"
      },
      "sideB": {
        "modality": "text",
        "value": "15 by 12 by 11 km, one orbit every 30 hours"
      },
      "source": {
        "label": "NASA Science — Deimos",
        "url": "https://science.nasa.gov/mars/moons/deimos/"
      },
      "tags": [
        "l05p2",
        "mars",
        "moons"
      ],
      "uid": "r4e611hg3ifd"
    },
    {
      "id": "ast-d-sol-martian-day",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Sol"
      },
      "definition": {
        "modality": "text",
        "value": "A Martian day measured Sun-to-Sun, 24 hours 39 minutes 35 seconds — about 3 percent longer than the Earth day it is so easily mistaken for"
      },
      "source": {
        "label": "NASA GISS — Mars24 Sunclock: Technical Notes on Mars Solar Time",
        "url": "https://www.giss.nasa.gov/tools/mars24/help/notes.html"
      },
      "tags": [
        "l05p2",
        "mars",
        "rotation"
      ],
      "uid": "13oqapum9u900"
    },
    {
      "id": "ast-q-mars-olympus-growth",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Why could one Martian volcano pile up so enormously?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Wind piled up the dust"
        },
        {
          "modality": "text",
          "value": "Its lava ran far thinner"
        },
        {
          "modality": "text",
          "value": "An impact pushed the rock up"
        },
        {
          "modality": "text",
          "value": "Its crust stayed in place"
        }
      ],
      "correctIndex": 3,
      "explanation": "With no plate tectonics the crust never slid off the hot spot, so eruptions stacked in one place instead of stringing out into an island chain. The sources credit that — not wind-piled dust, not an impact, not gravity. Olympus Mons is built of lava, over 600 km across at the base.",
      "source": {
        "label": "NASA Science Photojournal — Olympus Mons",
        "url": "https://science.nasa.gov/photojournal/olympus-mons/"
      },
      "tags": [
        "l05p2",
        "mars",
        "volcano"
      ],
      "uid": "4vmdl1r27mzv"
    },
    {
      "id": "ast-q-mars-year-length",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "How long does one lap around the Sun take on Mars?"
      },
      "options": [
        {
          "modality": "text",
          "value": "687 Earth days"
        },
        {
          "modality": "text",
          "value": "365 Earth days"
        },
        {
          "modality": "text",
          "value": "1,374 Earth days"
        },
        {
          "modality": "text",
          "value": "254 Earth days"
        }
      ],
      "correctIndex": 0,
      "explanation": "NASA gives 687 Earth days, or 669.6 sols — nearly twice the 365.25 of Earth, because Mars orbits half again as far out. A sol is only 3 percent longer than an Earth day, so day length is no guide: 254 undercuts even Earth's year and 1,374 doubles the real figure.",
      "source": {
        "label": "NASA Science — Mars: Facts",
        "url": "https://science.nasa.gov/mars/facts/"
      },
      "tags": [
        "l05p2",
        "mars",
        "orbit"
      ],
      "uid": "ccgj213la2gd"
    },
    {
      "id": "czr-ast-d-sol-martian-day",
      "shape": "cloze",
      "derivedFrom": "ast-d-sol-martian-day",
      "template": "___ — A Martian day measured Sun-to-Sun, 24 hours 39 minutes 35 seconds — about 3 percent longer than the Earth day it is so easily mistaken for",
      "answer": "Sol",
      "distractors": [
        "Synodic month",
        "Equinox",
        "Solar flare"
      ],
      "explanation": "Sol is a Martian solar day of 24 hours 39 minutes 35 seconds. Synodic month, the closest of the alternatives, is the 29.53-day round trip from one new Moon to the next, timed against the Sun rather than against the background stars.",
      "source": {
        "label": "NASA GISS — Mars24 Sunclock: Technical Notes on Mars Solar Time",
        "url": "https://www.giss.nasa.gov/tools/mars24/help/notes.html"
      },
      "tags": [
        "l05p2",
        "mars",
        "rotation",
        "derived"
      ],
      "uid": "udxzenfjto4j"
    },
    {
      "id": "tfr-ast-d-sol-martian-day",
      "shape": "trueFalse",
      "derivedFrom": "ast-d-sol-martian-day",
      "statement": "Sol — one body passing in front of a star, where the pattern of the starlight's dimming maps structures far too faint to photograph.",
      "isTrue": false,
      "why": "Occultation is the name for one body passing in front of a star, where the pattern of the starlight's dimming maps structures far too faint to photograph. A sol is a unit of time on Mars: one Martian solar day, 24 hours 39 minutes 35 seconds, some forty minutes longer than Earth's.",
      "source": {
        "label": "NASA GISS — Mars24 Sunclock: Technical Notes on Mars Solar Time",
        "url": "https://www.giss.nasa.gov/tools/mars24/help/notes.html"
      },
      "tags": [
        "l05p2",
        "mars",
        "rotation",
        "derived"
      ],
      "whyOptions": [
        "Equinox",
        "Occultation",
        "Synodic month"
      ],
      "whyCorrectIndex": 1,
      "uid": "6er1t412a292y"
    },
    {
      "id": "ast-f-mars-tenth-of-mass",
      "shape": "fact",
      "title": "A Tenth, Not a Half",
      "body": "Mars is roughly half Earth's width, which makes it sound like half a planet. It is not. Mars carries about **a tenth** of Earth's mass — 0.642 against 5.972 × 10^24 kg — because volume goes as the **cube** of the radius. Mass, not width, is what sets how hard a world grips its air, and across the four rocky planets it spans a factor of eighteen.",
      "source": {
        "label": "JPL Solar System Dynamics — Planetary Physical Parameters",
        "url": "https://ssd.jpl.nasa.gov/planets/phys_par.html"
      },
      "tags": [
        "l05p3",
        "mars",
        "mass"
      ],
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "Mars and Earth size and mass comparison to scale diagram",
        "imagePrompt": "Flat vector comparison: Mars and Earth drawn to true relative diameter side by side, with a second row of scaled blocks showing the far larger difference in mass.",
        "alt": "The Mars frame from the Voyager Golden Record: a black-and-white NASA photograph of the planet Mars showing the Tharsis volcanoes and Olympus Mons as dark spots and a bright polar cap, annotated…",
        "depictable": true,
        "allowGenerated": true,
        "subject": "The Mars frame from the Voyager Golden Record: a black-and-white NASA photograph of the planet Mars showing the Tharsis volcanoes and Olympus Mons as dark spots and a bright polar cap, annotated \"6787 km\" for its diameter and \"1/10 e\" for its mass as a fraction of Earth's.",
        "credit": "Wikimedia Commons · File:Voyager Golden Record 010. Mars.png",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:Voyager_Golden_Record_010._Mars.png",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-mars-tenth-of-mass.webp"
      },
      "uid": "iz4pid10w1ecj"
    },
    {
      "id": "ast-f-mars-same-gas-as-venus",
      "shape": "fact",
      "title": "Same Gas, Different Amount",
      "body": "Mars's air is **95.3 percent carbon dioxide**, with nitrogen at 2.7 and argon at 1.6 — chemically the same recipe as Venus's. The difference between a freezer and an oven is **quantity, not kind**: Martian surface pressure is less than **one hundredth** of Earth's average. Being half again further out, at 1.524 au, sets how much sunlight arrives, but does not by itself fix a surface temperature.",
      "source": {
        "label": "NASA JPL — InSight Landing Press Kit: Mars at a Glance",
        "url": "https://www.jpl.nasa.gov/news/press_kits/insight/landing/facts/mars-at-a-glance/"
      },
      "tags": [
        "l05p3",
        "mars",
        "atmosphere"
      ],
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "Mars and Venus atmospheric composition and surface pressure comparison chart",
        "imagePrompt": "Flat vector chart: two matching composition bars for Mars and Venus, each about 95 percent carbon dioxide, beside a logarithmic pressure scale where Venus sits at 92 bar and Mars below 0.01.",
        "alt": "A 3D render of the planet Mars, fully lit against a starfield, showing its Syrtis Major hemisphere: the dark Syrtis Major wedge with the bright circular Hellas basin below it on a rust-orange…",
        "depictable": true,
        "allowGenerated": true,
        "subject": "A 3D render of the planet Mars, fully lit against a starfield, showing its Syrtis Major hemisphere: the dark Syrtis Major wedge with the bright circular Hellas basin below it on a rust-orange cratered surface. No text or logos; not a chart.",
        "credit": "Pexels · High-resolution image of Mars shining in the vast universe, showcasing its surface details.",
        "creditUrl": "https://www.pexels.com/photo/moon-in-space-12498801/",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-mars-same-gas-as-venus.webp"
      },
      "uid": "1qyaalc1g997i4"
    },
    {
      "id": "ast-f-mars-maven-loss-rate",
      "shape": "fact",
      "title": "A Hundred Grams a Second",
      "body": "**MAVEN** measured the **solar wind** stripping gas from Mars at about **100 grams per second** — roughly a quarter of a pound, every second — and found the erosion increases significantly during solar storms. It was never one catastrophe. Run that slow drip for billions of years under a far more active young Sun and it empties a planet. It is still going.",
      "factVariant": "image-heavy",
      "imageCaption": "A quarter of a pound a second, for billions of years.",
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "MAVEN spacecraft measuring solar wind stripping the Martian atmosphere",
        "entityTerm": "MAVEN",
        "imagePrompt": "Illustration of Mars with solar wind streaming in from one side and a plume of escaping atmospheric ions drawn away on the other, the MAVEN spacecraft in orbit measuring it.",
        "alt": "Illustration of the solar wind sweeping past Mars and carrying atmospheric gas away downstream, with MAVEN measuring the outflow",
        "depictable": true
      },
      "source": {
        "label": "NASA — Mission Reveals Speed of Solar Wind Stripping Martian Atmosphere (5 Nov 2015)",
        "url": "https://www.nasa.gov/news-release/nasa-mission-reveals-speed-of-solar-wind-stripping-martian-atmosphere/"
      },
      "tags": [
        "l05p3",
        "mars",
        "atmospheric-loss"
      ],
      "uid": "a69qbb186zcbx"
    },
    {
      "id": "ast-f-earth-magnetosphere-field",
      "shape": "fact",
      "title": "A Field, Not a Shell",
      "body": "Earth's **magnetosphere** comes from its molten nickel-iron core, and NASA says it shields us from erosion of our atmosphere by the solar wind. It is a **field**, not a shell: charged particles are deflected, and neutral atoms pass straight through. Mars has no global field today — only patches of southern crust thought to have been magnetised some **4 billion years** ago. But the tidy conclusion fails: Venus has no dynamo either and was not stripped bare. Its carbon sits in its sky rather than filed away in rock, the way most of Earth's is.",
      "source": {
        "label": "NASA Science — Earth's Magnetosphere: Protecting Our Planet from Harmful Space Energy (3 Aug 2021)",
        "url": "https://science.nasa.gov/science-research/earth-science/earths-magnetosphere-protecting-our-planet-from-harmful-space-energy/"
      },
      "tags": [
        "l05p3",
        "earth",
        "magnetism"
      ],
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "Earth magnetosphere diagram solar wind bow shock magnetotail",
        "imagePrompt": "Flat vector diagram of Earth's magnetosphere: field lines compressed on the sunward side into a bow shock, drawn out downwind into a long magnetotail, with solar wind particle paths deflected around it.",
        "alt": "Diagram of Earth's magnetosphere as a field deflecting the solar wind into a bow shock and a long tail — not a shell around the planet",
        "depictable": true,
        "allowGenerated": true
      },
      "uid": "vlpu8lf728v9"
    },
    {
      "id": "ast-f-mars-polar-dry-ice",
      "shape": "fact",
      "title": "Air That Freezes Each Winter",
      "body": "Mars's polar caps are made of two different ices. Each winter a seasonal cap of frozen carbon dioxide — **dry ice** — condenses straight out of the air, and then **sublimates** away again in spring. What is left at the south pole is a residual dry-ice deposit sitting on much older **water ice**. Part of the atmosphere lands on the ground every year and comes back.",
      "factVariant": "image-heavy",
      "imageCaption": "Not Antarctic snow — much of that white is frozen carbon dioxide.",
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Mars south polar residual ice cap orbiter image",
        "entityTerm": "Martian polar ice caps",
        "imagePrompt": "An orbital photograph of the Martian south polar residual cap: bright ice pocked with rounded flat-floored depressions against darker terrain.",
        "alt": "Mars Global Surveyor orbiter view of the bright white residual south polar cap of Mars in southern summer 2000: a swirl of layered ice cut by dark curving troughs, sitting on rust-brown Martian…",
        "depictable": true,
        "credit": "NASA/JPL/MSSS · Public domain",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:South_Polar_Cap_of_Mars_during_Martian_South_summer_2000.jpg",
        "subject": "Mars Global Surveyor orbiter view of the bright white residual south polar cap of Mars in southern summer 2000: a swirl of layered ice cut by dark curving troughs, sitting on rust-brown Martian terrain.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-mars-polar-dry-ice.webp"
      },
      "source": {
        "label": "NASA Science — The Changing Ice Cap of Mars",
        "url": "https://science.nasa.gov/resource/the-changing-ice-cap-of-mars/"
      },
      "tags": [
        "l05p3",
        "mars",
        "polar-caps"
      ],
      "uid": "4flrke1494vqy"
    },
    {
      "id": "ast-p-sputtering-loss",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Sputtering"
      },
      "sideB": {
        "modality": "text",
        "value": "Solar-wind ions knocking atmospheric gas into space",
        "short": "Ions knocking gas off a planet"
      },
      "source": {
        "label": "NASA — MAVEN Reveals Most of Mars' Atmosphere Was Lost to Space (30 Mar 2017)",
        "url": "https://www.nasa.gov/news-release/nasas-maven-reveals-most-of-mars-atmosphere-was-lost-to-space/"
      },
      "tags": [
        "l05p3",
        "mars",
        "atmospheric-loss"
      ],
      "uid": "1mmpbk414t9pjy"
    },
    {
      "id": "ast-p-earth-carbon-in-rock",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Earth's carbon"
      },
      "sideB": {
        "modality": "text",
        "value": "Mostly locked in rock, not in the sky like Venus's",
        "short": "Locked in rock, not the sky"
      },
      "source": {
        "label": "NASA Earth Observatory — The Carbon Cycle",
        "url": "https://science.nasa.gov/earth/earth-observatory/the-carbon-cycle/"
      },
      "tags": [
        "l05p3",
        "earth",
        "carbon-cycle"
      ],
      "uid": "dwgfs313nq9c9"
    },
    {
      "id": "ast-d-escape-speed",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Escape speed"
      },
      "definition": {
        "modality": "text",
        "value": "The speed a molecule must reach to leave a planet's gravity for good, with a textbook rule of thumb that a gas begins to leak away once its average molecular speed passes about a sixth of that figure"
      },
      "source": {
        "label": "Catling & Kasting, Atmospheric Evolution on Inhabited and Lifeless Worlds, Ch. 5 (Cambridge University Press, 2017)",
        "url": "https://sseh.uchicago.edu/doc/Catling_and_Kasting_ch_5.pdf"
      },
      "tags": [
        "l05p3",
        "planets",
        "atmospheric-loss"
      ],
      "uid": "187xp611bafm0d"
    },
    {
      "id": "ast-q-mars-argon-accounting",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "What does the argon accounting say became of Mars's original air?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Most of it reacted with rock"
        },
        {
          "modality": "text",
          "value": "Most of it is still up there"
        },
        {
          "modality": "text",
          "value": "Most of it froze into the ground"
        },
        {
          "modality": "text",
          "value": "Most of it went to space"
        }
      ],
      "correctIndex": 3,
      "explanation": "MAVEN found about 65 percent of the argon Mars ever had has been lost to space by sputtering. Argon cannot react chemically, so rock cannot hold it, and 65 percent gone means it is not still up there. Some carbon dioxide did freeze into the ground, but the bulk of the gas left.",
      "source": {
        "label": "NASA — MAVEN Reveals Most of Mars' Atmosphere Was Lost to Space (30 Mar 2017)",
        "url": "https://www.nasa.gov/news-release/nasas-maven-reveals-most-of-mars-atmosphere-was-lost-to-space/"
      },
      "tags": [
        "l05p3",
        "mars",
        "atmospheric-loss"
      ],
      "uid": "t7hv24110sggc"
    },
    {
      "id": "ast-q-mars-escape-energy",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Leaving Mars costs a molecule how much energy, next to leaving Earth?"
      },
      "options": [
        {
          "modality": "text",
          "value": "About half"
        },
        {
          "modality": "text",
          "value": "About the same"
        },
        {
          "modality": "text",
          "value": "About a quarter"
        },
        {
          "modality": "text",
          "value": "About twice as much"
        }
      ],
      "correctIndex": 2,
      "explanation": "Mars is roughly half Earth's diameter, so its escape speed is roughly half — 5.03 km/s against 11.19. Escape energy goes as the square of speed, so the bill is about a quarter: not half, not the same, and certainly not larger. Halving a planet does not halve the difficulty.",
      "source": {
        "label": "Catling & Kasting, Atmospheric Evolution on Inhabited and Lifeless Worlds, Ch. 5 (Cambridge University Press, 2017)",
        "url": "https://sseh.uchicago.edu/doc/Catling_and_Kasting_ch_5.pdf"
      },
      "tags": [
        "l05p3",
        "mars",
        "atmospheric-loss"
      ],
      "uid": "xhe9escjejm4"
    },
    {
      "id": "ast-q-atmosphere-light-gases-first",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "When a planet loses atmosphere, which gases go first?"
      },
      "options": [
        {
          "modality": "text",
          "value": "The most reactive ones"
        },
        {
          "modality": "text",
          "value": "The lightest ones"
        },
        {
          "modality": "text",
          "value": "All of them together"
        },
        {
          "modality": "text",
          "value": "The heaviest ones"
        }
      ],
      "correctIndex": 1,
      "explanation": "Lighter molecules move faster at a given temperature, so hydrogen and helium leave while carbon dioxide and nitrogen hang on longest — heaviest-first is backwards. At Venus, roughly twice as many hydrogen as oxygen atoms were escaping. Loss is filtered by mass, not reactivity, and never uniform.",
      "source": {
        "label": "Catling & Kasting, Atmospheric Evolution on Inhabited and Lifeless Worlds, Ch. 5 (Cambridge University Press, 2017)",
        "url": "https://sseh.uchicago.edu/doc/Catling_and_Kasting_ch_5.pdf"
      },
      "tags": [
        "l05p3",
        "planets",
        "atmospheric-loss"
      ],
      "uid": "l4dilq1j7e07m"
    },
    {
      "id": "tfr-ast-d-escape-speed",
      "shape": "trueFalse",
      "derivedFrom": "ast-d-escape-speed",
      "statement": "Escape speed — the equatorial bulge a spinning world takes on, given as the fraction of the equatorial radius by which it exceeds the polar one.",
      "isTrue": false,
      "why": "Escape speed is the speed a molecule must reach to leave a planet's gravity for good, and a textbook rule of thumb has a gas beginning to leak away once its average molecular speed passes about a sixth of that figure. Oblateness is a shape: the equatorial bulge a spinning world takes on.",
      "source": {
        "label": "Catling & Kasting, Atmospheric Evolution on Inhabited and Lifeless Worlds, Ch. 5 (Cambridge University Press, 2017)",
        "url": "https://sseh.uchicago.edu/doc/Catling_and_Kasting_ch_5.pdf"
      },
      "tags": [
        "l05p3",
        "planets",
        "atmospheric-loss",
        "derived"
      ],
      "whyOptions": [
        "Airmass",
        "Apparent magnitude",
        "Oblateness"
      ],
      "whyCorrectIndex": 2,
      "uid": "pgkk7o17xo6py"
    },
    {
      "id": "ast-f-jupiter-mass-class",
      "shape": "fact",
      "title": "Jupiter Plus Debris",
      "body": "Jupiter carries about **318 times Earth's mass**. NASA puts that at more than twice the combined material of the other bodies orbiting the Sun; against the other seven planets alone the ratio is close to **2.5 times their combined mass**. So the eight planets are not eight comparable objects that happen to differ in size. After the Sun, the Solar System is Jupiter plus debris — and Earth is in the debris. It sits **5.2 astronomical units** out.",
      "factVariant": "image-heavy",
      "imageCaption": "Jupiter outweighs the other seven planets put together, about two and a half times over.",
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "Jupiter mass compared with all other planets combined bar chart",
        "imagePrompt": "Flat vector bar chart: one tall bar for Jupiter at 318 Earth masses beside a shorter combined bar for all other planets, with an inset showing both as a sliver against the Sun.",
        "alt": "Bar chart setting Jupiter's mass against the other seven planets put together, and the whole lot against the Sun",
        "depictable": true,
        "allowGenerated": true
      },
      "source": {
        "label": "NASA Science — Jupiter Facts",
        "url": "https://science.nasa.gov/jupiter/facts/"
      },
      "tags": [
        "l06p1",
        "jupiter",
        "mass"
      ],
      "uid": "6zcsx44amdzi"
    },
    {
      "id": "ast-f-jupiter-eleven-wide",
      "shape": "fact",
      "title": "Eleven Wide, Thousand Deep",
      "body": "Jupiter's mean radius is **69,911 km**, about **11 times Earth's**. Eleven times wider is not eleven times bigger: volume scales as the cube, so eleven cubed leaves **well over a thousand Earths' worth of room** inside. The planet also bulges — the equatorial radius is 71,492 km — so even \"the radius\" is a choice of which one you mean.",
      "source": {
        "label": "NASA Science — Jupiter Facts",
        "url": "https://science.nasa.gov/jupiter/jupiter-facts/"
      },
      "tags": [
        "l06p1",
        "jupiter",
        "size"
      ],
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "Jupiter and Earth diameter comparison to scale diagram",
        "imagePrompt": "Flat scale diagram with Jupiter's banded disc filling most of the frame and Earth drawn to true relative size against it, annotated with the 11x diameter and >1,000x volume ratios.",
        "alt": "Jupiter alone against black space: an oblate, gibbous-lit disc with pale zones and two prominent tan equatorial belts, no rings, no Earth and no scale markings in frame.",
        "depictable": true,
        "allowGenerated": true,
        "subject": "Jupiter alone against black space: an oblate, gibbous-lit disc with pale zones and two prominent tan equatorial belts, no rings, no Earth and no scale markings in frame. Probably a CGI render on a Jupiter texture map (Pexels, Zelch Csaba) rather than a spacecraft photograph, but the banding shown is",
        "credit": "Pexels · High-resolution image of Jupiter showcasing its beautiful bands and clouds.",
        "creditUrl": "https://www.pexels.com/photo/planet-in-space-20337598/",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-jupiter-eleven-wide.webp"
      },
      "uid": "lsycvh14kbful"
    },
    {
      "id": "ast-f-jupiter-no-surface",
      "shape": "fact",
      "title": "Nowhere to Land",
      "body": "Jupiter has **no true surface**. There is no boundary where atmosphere stops and ground begins; the gas simply thickens with depth into hot, dense liquid, so nothing lands on it. Every radius and temperature quoted for Jupiter therefore belongs to an agreed pressure depth — the **1-bar level** — rather than to any ground. At the cloud tops it is about **minus 145 °C**, while the interior runs to thousands of degrees. A planet like this has no single temperature.",
      "source": {
        "label": "NASA Science — Jupiter Facts",
        "url": "https://science.nasa.gov/jupiter/jupiter-facts/"
      },
      "tags": [
        "l06p1",
        "jupiter",
        "atmosphere"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Jupiter full disc Hubble OPAL portrait cloud tops",
        "entityTerm": "Jupiter",
        "imagePrompt": "A full-disc portrait of Jupiter showing its belts, zones and Great Red Spot in sharp detail against black space.",
        "alt": "The full disc of Jupiter against a black background: alternating cream, tan and orange-brown cloud belts and zones, with the Great Red Spot and several small white oval storms visible, and no…",
        "depictable": true,
        "credit": "Pexels · Zelch Csaba · Pexels License",
        "creditUrl": "https://www.pexels.com/photo/jupiter-planet-on-black-background-20337602/",
        "subject": "The full disc of Jupiter against a black background: alternating cream, tan and orange-brown cloud belts and zones, with the Great Red Spot and several small white oval storms visible, and no surface features of any kind.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-jupiter-no-surface.webp"
      },
      "uid": "1vx8yj21vgxnwc"
    },
    {
      "id": "ast-f-jupiter-star-ingredients",
      "shape": "fact",
      "title": "Star Ingredients, Never Lit",
      "body": "The upper atmosphere is **89.8 percent molecular hydrogen** and 10.2 percent helium, with methane and ammonia as traces — close to stellar proportions. The colours are trace compounds sitting on plain hydrogen and helium, not exotic chemistry. Same ingredients as a star, and it never lit. Not nearly: hydrogen fusion needs roughly **80 times Jupiter's mass**. \"Failed star\" is a slogan, not a near miss.",
      "source": {
        "label": "NASA GSFC — Jupiter Fact Sheet (Radio JOVE Project)",
        "url": "https://radiojove.gsfc.nasa.gov/education/jupiter/basics/jfacts.htm"
      },
      "tags": [
        "l06p1",
        "jupiter",
        "composition"
      ],
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "Jupiter and Sun composition comparison hydrogen helium chart",
        "imagePrompt": "Flat vector chart: paired composition bars for Jupiter and the Sun, both dominated by hydrogen and helium, beside a mass scale marking Jupiter and the roughly 80-Jupiter-mass hydrogen fusion threshold.",
        "alt": "Chart setting Jupiter's hydrogen and helium proportions beside the Sun's, and the eighty-fold mass gap that separates them",
        "depictable": true,
        "allowGenerated": true
      },
      "uid": "4ldvo1nq9q19"
    },
    {
      "id": "ast-f-jupiter-shoemaker-levy",
      "shape": "fact",
      "title": "Twenty-One Fragments",
      "body": "In July 1994 comet **Shoemaker-Levy 9** broke into some 21 pieces that struck Jupiter over six days — the first collision between two Solar System bodies humanity was able to watch happen. Whether that reach shields Earth is genuinely unsettled: simulations by Horner and Jones found a giant planet can significantly **enhance** Earth's asteroid impact rate, while the same authors found the Oort-cloud comet rate falling as the giant's mass rises.",
      "source": {
        "label": "NASA Science — The Lasting Impacts of Comet Shoemaker-Levy 9",
        "url": "https://science.nasa.gov/science-research/planetary-science/the-lasting-impacts-comet-shoemaker-levy-9/"
      },
      "tags": [
        "l06p1",
        "jupiter",
        "impacts"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Comet Shoemaker-Levy 9 fragment chain Hubble 1994 image",
        "entityTerm": "Comet Shoemaker–Levy 9",
        "imagePrompt": "A Hubble image of comet Shoemaker-Levy 9 as a beaded chain of bright fragments strung out in a line, each trailing its own small coma.",
        "alt": "The string of fragments of comet Shoemaker-Levy 9 lined up along its orbit before they struck Jupiter",
        "depictable": true,
        "credit": "NASA, ESA, H. Weaver and E. Smith (STScI) and J. Trauger and R. Evans (NASA's Je · Public domain",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:Comet_Shoemaker-Levy_9_Approaching_Jupiter_in_1994.jpg",
        "subject": "The famous Hubble Space Telescope image 'Comet Shoemaker-Levy 9 Approaching Jupiter in 1994': Jupiter's banded disk with a diagonal chain of roughly 20 bright fragment nuclei strung out below it along the comet's orbital path -- exactly the fragment-chain subject the card describes.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-jupiter-shoemaker-levy.webp"
      },
      "uid": "1wqdtcihp0soq"
    },
    {
      "id": "ast-d-metallic-hydrogen",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Metallic hydrogen"
      },
      "definition": {
        "modality": "text",
        "value": "A liquid squeezed until its electrons run free, so it conducts electricity like a metal while remaining the lightest element — no iron involved"
      },
      "source": {
        "label": "NASA Science — Jupiter Facts",
        "url": "https://science.nasa.gov/jupiter/jupiter-facts/"
      },
      "tags": [
        "l06p1",
        "jupiter",
        "interior"
      ],
      "uid": "lxznrws0s0ls"
    },
    {
      "id": "ast-p-jupiter-day-length",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Jupiter's day"
      },
      "sideB": {
        "modality": "text",
        "value": "9.925 hours — the shortest of any planet"
      },
      "source": {
        "label": "NASA GSFC — Jupiter Fact Sheet (Radio JOVE Project)",
        "url": "https://radiojove.gsfc.nasa.gov/education/jupiter/basics/jfacts.htm"
      },
      "tags": [
        "l06p1",
        "jupiter",
        "rotation"
      ],
      "uid": "ot6cyd19jw2rd"
    },
    {
      "id": "ast-p-jupiter-year-length",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Jupiter's year"
      },
      "sideB": {
        "modality": "text",
        "value": "4,332 days — about 11.86 Earth years"
      },
      "source": {
        "label": "NASA GSFC — Jupiter Fact Sheet (Radio JOVE Project)",
        "url": "https://radiojove.gsfc.nasa.gov/education/jupiter/basics/jfacts.htm"
      },
      "tags": [
        "l06p1",
        "jupiter",
        "orbit"
      ],
      "uid": "1d6bdaw3lk8k0"
    },
    {
      "id": "ast-q-jupiter-fusion-threshold",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "How much more massive would Jupiter have to be before hydrogen fusion could begin?"
      },
      "options": [
        {
          "modality": "text",
          "value": "About 2 times its own mass"
        },
        {
          "modality": "text",
          "value": "About 25 times its own mass"
        },
        {
          "modality": "text",
          "value": "About 80 times its own mass"
        },
        {
          "modality": "text",
          "value": "About 8 times its own mass"
        }
      ],
      "correctIndex": 2,
      "explanation": "Fusion needs roughly 80 Jupiter masses, so Jupiter falls short by a factor of about 80 — not by a little. At 2, 8 or 25 times its mass it would still be a planet or a brown dwarf and never a star. \"Failed star\" is a slogan, not a near miss.",
      "source": {
        "label": "NASA Science — Jupiter Facts",
        "url": "https://science.nasa.gov/jupiter/jupiter-facts/"
      },
      "tags": [
        "l06p1",
        "jupiter",
        "fusion"
      ],
      "uid": "17kw3edrjinj1"
    },
    {
      "id": "ast-q-jupiter-cloud-gravity",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Jupiter holds 318 Earths' worth of material. What is the pull at its cloud tops?"
      },
      "options": [
        {
          "modality": "text",
          "value": "About 318 times Earth's"
        },
        {
          "modality": "text",
          "value": "About 11 times Earth's"
        },
        {
          "modality": "text",
          "value": "About 2.4 times Earth's"
        },
        {
          "modality": "text",
          "value": "About 59 times Earth's"
        }
      ],
      "correctIndex": 2,
      "explanation": "Gravity goes as mass divided by radius squared, and the radius is enormous: 23.12 m/s² at the 1-bar equator, 2.364 times Earth's. 318 mistakes mass for gravity, 11 is the width ratio, and 59 is the escape velocity in km/s — a speed, not a gravity.",
      "source": {
        "label": "NASA GSFC — Jupiter Fact Sheet (Radio JOVE Project)",
        "url": "https://radiojove.gsfc.nasa.gov/education/jupiter/basics/jfacts.htm"
      },
      "tags": [
        "l06p1",
        "jupiter",
        "gravity"
      ],
      "uid": "ty2q4215ujbg"
    },
    {
      "id": "ast-f-jupiter-red-spot",
      "shape": "fact",
      "title": "Three Centuries of Storm",
      "body": "The **Great Red Spot** is a single storm watched for **more than 300 years** and still wider than the Earth. With no continents and no ocean surface to drain its energy, a Jovian storm can outlive every human who has observed it. It is also shrinking: observations from the late 1800s put its long axis near 25,500 miles, Voyager measured 14,500 in 1979, and Hubble measured about **10,250 miles** in 2014 — the smallest ever measured to that date. Any single size is a dated snapshot.",
      "factVariant": "image-heavy",
      "imageCaption": "A storm watched for three centuries, and measurably smaller each time it is measured.",
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Great Red Spot Jupiter JunoCam close-up",
        "entityTerm": "Great Red Spot",
        "imagePrompt": "A close JunoCam-style photograph of Jupiter's Great Red Spot filling much of the frame, its spiral structure and the turbulent white cloud around its edges clearly resolved.",
        "alt": "A close-range JunoCam view of Jupiter's Great Red Spot: a vast oval orange-red storm with swirling interior filaments, surrounded by cream and blue-grey cloud bands.",
        "depictable": true,
        "credit": "Wikipedia — Great Red Spot · See Wikimedia Commons",
        "creditUrl": "https://en.wikipedia.org/wiki/Great_Red_Spot",
        "subject": "A close-range JunoCam view of Jupiter's Great Red Spot: a vast oval orange-red storm with swirling interior filaments, surrounded by cream and blue-grey cloud bands.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-jupiter-red-spot.webp"
      },
      "source": {
        "label": "NASA Science — Jupiter Facts",
        "url": "https://science.nasa.gov/jupiter/jupiter-facts/"
      },
      "tags": [
        "l06p2",
        "jupiter",
        "storms"
      ],
      "uid": "myt9bk1l8t2gq"
    },
    {
      "id": "ast-f-jupiter-oblate",
      "shape": "fact",
      "title": "Spin Made Visible",
      "body": "Jupiter's equatorial radius is 71,492 km against a polar radius of 66,854 km — an **ellipticity** of **0.06487**, about **twenty times Earth's** flattening. That 4,638 km bulge is the fast spin made visible, and it is large enough to see through an amateur telescope. A fast-spinning fluid body is not a sphere but a measurably squashed ellipsoid.",
      "source": {
        "label": "NASA GSFC — Jupiter Fact Sheet (Radio JOVE Project)",
        "url": "https://radiojove.gsfc.nasa.gov/education/jupiter/basics/jfacts.htm"
      },
      "tags": [
        "l06p2",
        "jupiter",
        "shape"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Jupiter portrait showing flattened poles and equatorial bulge",
        "entityTerm": "Jupiter",
        "imagePrompt": "A full-disc photograph of Jupiter framed square-on so the oblate shape reads clearly, the equatorial diameter noticeably greater than the polar one.",
        "alt": "Jupiter photographed so that its flattening is obvious: the equator visibly wider than the pole-to-pole span",
        "depictable": true,
        "credit": "Pexels · Zelch Csaba · Pexels License",
        "creditUrl": "https://www.pexels.com/photo/jupiter-planet-on-black-background-20337602/",
        "subject": "Jupiter's full disc on plain black space background: cream/tan cloud bands and the Great Red Spot, rendered as a near-perfect circle with no visible equatorial widening",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-jupiter-oblate.webp"
      },
      "uid": "1rm3bzpl73bk7"
    },
    {
      "id": "ast-f-jupiter-belts-zones",
      "shape": "fact",
      "title": "The Stripes Are Weather",
      "body": "The pale bands are **zones**, the dark ones **belts**. On the simplest interpretation zones are where gas rises and is topped with bright **ammonia-ice cloud**, while belts are where it sinks and deeper, darker cloud shows through. Treat that as a cloud-top picture only: Juno's microwave sounding indicates the circulation is stacked and can reverse with depth. Either way the bands are not paint — belts and zones change appearance from year to year.",
      "source": {
        "label": "Wikipedia — Atmosphere of Jupiter",
        "url": "https://en.wikipedia.org/wiki/Atmosphere_of_Jupiter"
      },
      "tags": [
        "l06p2",
        "jupiter",
        "clouds"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Jupiter belts and zones cloud bands JunoCam",
        "entityTerm": "Atmosphere of Jupiter",
        "imagePrompt": "A close photograph of Jupiter's cloud tops filling the frame with alternating bright zones and dark belts, curling vortices along the boundaries between them.",
        "alt": "A full-disc view of Jupiter on a black background, lit from the left, showing its alternating pale zones and tan belts — the bright Equatorial Zone between the two dark equatorial belts, white…",
        "depictable": true,
        "subject": "A full-disc view of Jupiter on a black background, lit from the left, showing its alternating pale zones and tan belts — the bright Equatorial Zone between the two dark equatorial belts, white ovals and small brown storms in the north, and turbulent swirls where belts and zones meet. It is a 3D rend",
        "credit": "Pexels · High-resolution image of Jupiter adorned with its iconic bands against a black background.",
        "creditUrl": "https://www.pexels.com/photo/jupiter-in-space-20337599/",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-jupiter-belts-zones.webp"
      },
      "uid": "1htw3ooj6byrq"
    },
    {
      "id": "ast-f-jupiter-field-no-iron",
      "shape": "fact",
      "title": "A Dynamo Without Iron",
      "body": "Circulating metallic hydrogen makes a dynamo, and this one is the strongest in the Solar System — NASA puts Jupiter's field at **16 to 54 times as powerful as Earth's**. No iron core is involved; a planet does not need one. The field inflates a **magnetosphere** about **5.3 million km** across on average, **about 38 times Jupiter’s own diameter** and nearly four times the width of the Sun, with a tail streaming downwind far beyond the orbits of the big moons.",
      "source": {
        "label": "NASA Science — Jupiter Facts",
        "url": "https://science.nasa.gov/jupiter/jupiter-facts/"
      },
      "tags": [
        "l06p2",
        "jupiter",
        "magnetism"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Jupiter ultraviolet aurora Hubble polar oval image",
        "entityTerm": "Aurora",
        "imagePrompt": "A Hubble ultraviolet image of Jupiter's north polar aurora: a bright oval of emission over the pole superimposed on the planet's disc.",
        "alt": "Jupiter's ultraviolet aurora ringing its pole — the strongest planetary magnetic field in the Solar System made visible",
        "depictable": true,
        "credit": "NASA, ESA &amp; John T. Clarke (Univ. of Michigan) · Public domain",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:Uncovering_the_mysteries_of_Jupiter%27s_aurora_(heic0009a).jpg",
        "subject": "Close-up false-color blue Hubble UV image of Jupiter's north polar region: a glowing auroral oval ringing the pole plus a separate bright spot (Io's magnetic footprint), no text overlay",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-jupiter-field-no-iron.webp"
      },
      "uid": "1aicdc5eysuk3"
    },
    {
      "id": "ast-f-jupiter-rings-moon-count",
      "shape": "fact",
      "title": "Rings, and a Moving Count",
      "body": "Jupiter has rings, found by **Voyager 1** in 1979 — faint, mostly small dark dust, arranged as an inner halo, a thin main ring and two broad gossamer rings. Saturn's are exceptional for being bright and icy, not for existing. The moon count moves too: NASA lists **101 moons** recognised by the IAU as of March 2026, while confirmed-detection catalogues listed 115 as of April 2026. Any figure here needs a date attached to it.",
      "source": {
        "label": "NASA Science — Jupiter Facts",
        "url": "https://science.nasa.gov/jupiter/jupiter-facts/"
      },
      "tags": [
        "l06p2",
        "jupiter",
        "rings"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Rings of Jupiter",
        "imagePrompt": "Documentary-style photograph: Jupiter's faint, dusty main ring seen backlit by a spacecraft. Natural light, no readable text, no logos, no watermarks.",
        "alt": "Jupiter's faint, dusty main ring seen backlit by a spacecraft",
        "credit": "Wikipedia — Rings of Jupiter · See Wikimedia Commons",
        "creditUrl": "https://en.wikipedia.org/wiki/Rings_of_Jupiter",
        "subject": "NASA/JPL diagram (PIA01627), the Wikipedia lead image for 'Rings of Jupiter': a photographic Jupiter with an overlaid, labeled schematic of the Halo, Main Ring, and two Gossamer Rings, plus orbit lines for the moons Metis, Adrastea, Amalthea and Thebe.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-jupiter-rings-moon-count.webp"
      },
      "uid": "wofn6s1dof778"
    },
    {
      "id": "ast-d-radiation-belt",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Radiation belt"
      },
      "definition": {
        "modality": "text",
        "value": "A zone where a planet's magnetic field traps and accelerates charged particles — at Jupiter stocked mainly by a volcanic moon rather than by the Sun"
      },
      "source": {
        "label": "Mission Juno (NASA/SwRI) — Magnetosphere",
        "url": "https://www.missionjuno.swri.edu/jupiter/magnetosphere/"
      },
      "tags": [
        "l06p2",
        "jupiter",
        "radiation"
      ],
      "uid": "1zfiuj7s3s9d"
    },
    {
      "id": "ast-p-jupiter-magnetosphere",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Jupiter's magnetosphere"
      },
      "sideB": {
        "modality": "text",
        "value": "5.3 million km across — about 38 times the planet"
      },
      "source": {
        "label": "Mission Juno (NASA/SwRI) — Magnetosphere",
        "url": "https://www.missionjuno.swri.edu/jupiter/magnetosphere/"
      },
      "tags": [
        "l06p2",
        "jupiter",
        "magnetism"
      ],
      "uid": "4c4f1rxsyv1t"
    },
    {
      "id": "ast-p-juno-polar-orbit",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Juno's looping orbit"
      },
      "sideB": {
        "modality": "text",
        "value": "Dives through the gap under the radiation belts"
      },
      "source": {
        "label": "NASA Science — Juno",
        "url": "https://science.nasa.gov/mission/juno/"
      },
      "tags": [
        "l06p2",
        "jupiter",
        "juno"
      ],
      "uid": "xx2k7plshw6h"
    },
    {
      "id": "ast-q-jupiter-belt-fuel",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "What supplies most of the material trapped in Jupiter's radiation belts?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Dust from the ring system"
        },
        {
          "modality": "text",
          "value": "Volcanic gas from Io"
        },
        {
          "modality": "text",
          "value": "Debris from comet impacts"
        },
        {
          "modality": "text",
          "value": "The solar wind"
        }
      ],
      "correctIndex": 1,
      "explanation": "Io loads the magnetosphere with as much as 1,000 kg of new material every second. The solar wind is the usual answer at Earth but not the dominant source here; the rings are faint dark dust, not feedstock; and comet impacts are occasional events, not a steady supply.",
      "source": {
        "label": "Mission Juno (NASA/SwRI) — Magnetosphere",
        "url": "https://www.missionjuno.swri.edu/jupiter/magnetosphere/"
      },
      "tags": [
        "l06p2",
        "jupiter",
        "radiation"
      ],
      "uid": "4oqx0on7wtf2"
    },
    {
      "id": "ast-q-jupiter-dynamo-source",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "What generates the strongest magnetic field of any planet in the Solar System?"
      },
      "options": [
        {
          "modality": "text",
          "value": "A molten iron core"
        },
        {
          "modality": "text",
          "value": "Charged dust in the rings"
        },
        {
          "modality": "text",
          "value": "Circulating metallic hydrogen"
        },
        {
          "modality": "text",
          "value": "Friction between cloud bands"
        }
      ],
      "correctIndex": 2,
      "explanation": "Jupiter's dynamo is a churning shell of hydrogen made conductive by pressure, which is why \"a field needs iron\" is wrong — there is no iron core to melt. Cloud bands are weather that changes yearly, and the rings are faint dust; neither drives a field 16 to 54 times Earth's.",
      "source": {
        "label": "NASA Science — Jupiter Facts",
        "url": "https://science.nasa.gov/jupiter/jupiter-facts/"
      },
      "tags": [
        "l06p2",
        "jupiter",
        "magnetism"
      ],
      "uid": "59ge8j18kt99r"
    },
    {
      "id": "czr-ast-d-radiation-belt",
      "shape": "cloze",
      "derivedFrom": "ast-d-radiation-belt",
      "template": "___ — A zone where a planet's magnetic field traps and accelerates charged particles — at Jupiter stocked mainly by a volcanic moon rather than by the Sun",
      "answer": "Radiation belt",
      "distractors": [
        "Penumbra",
        "Coronal hole",
        "Exosphere"
      ],
      "explanation": "Radiation belt is a zone where a planet's magnetic field traps and accelerates charged particles. Penumbra, the closest of the alternatives, is the outer part of a shadow, where the light source is partly blocked rather than hidden completely.",
      "source": {
        "label": "Mission Juno (NASA/SwRI) — Magnetosphere",
        "url": "https://www.missionjuno.swri.edu/jupiter/magnetosphere/"
      },
      "tags": [
        "l06p2",
        "jupiter",
        "radiation",
        "derived"
      ],
      "uid": "240rga2hxbj2"
    },
    {
      "id": "ast-f-galileo-four-points",
      "shape": "fact",
      "title": "Four Points Beside Jupiter",
      "body": "On **7 January 1610** Galileo Galilei pointed an improved homemade telescope at Jupiter and found four objects beside it, published that March in ***Sidereus Nuncius***. The argument was geometric, not rhetorical: four things plainly circling something that was not the Earth. That did not prove the Earth goes round the Sun. It proved something narrower and much harder to argue with — that not everything goes round us.",
      "source": {
        "label": "NASA — 415 Years Ago: Astronomer Galileo Discovers Jupiter's Moons",
        "url": "https://www.nasa.gov/general/415-years-ago-astronomer-galileo-discovers-jupiters-moons"
      },
      "tags": [
        "l06p3",
        "galilean-moons",
        "history"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Sidereus Nuncius Medicean stars diagram",
        "imagePrompt": "Documentary-style photograph: A page from Galileo's 1610 Sidereus Nuncius recording his night-by-night observations of the four Medicean Stars beside Jupiter. Natural light, no readable text, no logos, no watermarks.",
        "alt": "A page from Galileo's 1610 Sidereus Nuncius recording his night-by-night observations of the four Medicean Stars beside Jupiter",
        "credit": "History of Science Collections, University of Oklahoma Libraries · CC BY 4.0",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:Sample_of_Sidereus_Nuncius_drawings_of_Jupiter_and_the_Medicean_Stars_(medicean_stars_iautheme).jpg",
        "subject": "A genuine page from Galileo's Sidereus Nuncius (Univ. of Oklahoma History of Science Collections) showing two nights of his notation: 'Ori.' and 'Occ.' labels, asterisks for the Medicean Stars, and a circle for Jupiter between them.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-galileo-four-points.webp"
      },
      "uid": "x9g4s91bu56bh"
    },
    {
      "id": "ast-f-galilean-resonance",
      "shape": "fact",
      "title": "A Lock That Makes Heat",
      "body": "The three inner moons are locked in a **1:2:4 rhythm** — Io orbits in about 1.77 days, Europa in about 3.55, Ganymede in about 7.155 — while Callisto, outside the lock, takes about 16.7 days. Those ratios are not coincidence but a self-sustaining gravitational relationship, and they hold the inner orbits slightly stretched. A stretched orbit flexes the moon as it travels, and flexing makes heat. That is **tidal heating**, and it is why distance from the Sun does not make a world cold and dead.",
      "source": {
        "label": "Wikipedia — Io (moon)",
        "url": "https://en.wikipedia.org/wiki/Io_(moon)"
      },
      "tags": [
        "l06p3",
        "galilean-moons",
        "resonance"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Galilean moons Io Europa Ganymede Callisto family portrait",
        "entityTerm": "Galilean moons",
        "imagePrompt": "A composite spacecraft portrait of Jupiter's four Galilean moons arranged in a row at true relative scale, each surface distinctly different.",
        "alt": "Io, Europa, Ganymede and Callisto shown together at their true relative sizes",
        "depictable": true,
        "credit": "NASA/JPL/DLR · Public domain",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:PIA01400_The_Galilean_Satellites.jpg",
        "subject": "NASA/JPL/DLR 'PIA01400 The Galilean Satellites': the four moons Io, Europa, Ganymede and Callisto shown as full disks in a row, in the correct order and at correct relative sizes, each with its correct real surface appearance — a direct match to the alt text",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-galilean-resonance.webp"
      },
      "uid": "16znf9k41gjuc"
    },
    {
      "id": "ast-f-io-four-hundred-volcanoes",
      "shape": "fact",
      "title": "Four Hundred Volcanoes",
      "body": "**Io** is only a little larger than our own Moon — a mean radius of 1,821 km — yet it is the most volcanically active world in the Solar System, with **over 400 active volcanoes** and sulfur plumes rising as high as about **500 km**. It is also nearly uncratered: eruptions resurface it faster than impacts can scar it. Geological activity does not scale with size.",
      "factVariant": "image-heavy",
      "imageCaption": "Sulfur plumes rise hundreds of kilometres from a moon barely larger than our own.",
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Io volcanic plume Galileo spacecraft image",
        "entityTerm": "Io (moon)",
        "imagePrompt": "A spacecraft image of Io with a large umbrella-shaped volcanic plume rising off the limb against black space, the mottled sulphurous surface below.",
        "alt": "NASA Galileo colour mosaic (PIA01081) of Jupiter's moon Io: the sulphur-yellow, crater-free disc with a bluish volcanic plume from Pillan Patera rising off the left limb into black space, and the…",
        "depictable": true,
        "credit": "NASA's Galileo spacecraft · Public domain",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:PIA01081-Color_Mosaic_and_Active_Volcanic_Plumes_on_Io.jpg",
        "subject": "NASA Galileo colour mosaic (PIA01081) of Jupiter's moon Io: the sulphur-yellow, crater-free disc with a bluish volcanic plume from Pillan Patera rising off the left limb into black space, and the ring-shaped Prometheus plume feature near the centre of the disc.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-io-four-hundred-volcanoes.webp"
      },
      "source": {
        "label": "NASA Science — Io",
        "url": "https://science.nasa.gov/jupiter/moons/io/"
      },
      "tags": [
        "l06p3",
        "galilean-moons",
        "io"
      ],
      "uid": "1deiibkw9m0ne"
    },
    {
      "id": "ast-d-tidal-heating",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Tidal heating"
      },
      "definition": {
        "modality": "text",
        "value": "Warmth made inside a body by the flexing of a stretched orbit, rather than by sunlight or by radioactive decay"
      },
      "source": {
        "label": "NASA Science — Io",
        "url": "https://science.nasa.gov/jupiter/moons/io/"
      },
      "tags": [
        "l06p3",
        "galilean-moons",
        "heating"
      ],
      "uid": "12vwo7t1h4r7w5"
    },
    {
      "id": "ast-p-europa-ice-shell",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Europa's ice shell"
      },
      "sideB": {
        "modality": "text",
        "value": "Estimated 10-30 km of ice over the ocean",
        "short": "est. 10-30 km of ice"
      },
      "source": {
        "label": "NASA JPL Solar System Dynamics — Planetary Satellite Physical Parameters",
        "url": "https://ssd.jpl.nasa.gov/sats/phys_par/"
      },
      "tags": [
        "l06p3",
        "galilean-moons",
        "europa"
      ],
      "uid": "1afcrm32ijdnd"
    },
    {
      "id": "ast-q-callisto-cratering",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "What separates Io's violent surface from Callisto's ancient one?"
      },
      "options": [
        {
          "modality": "text",
          "value": "How much ice each began with"
        },
        {
          "modality": "text",
          "value": "The size of each moon"
        },
        {
          "modality": "text",
          "value": "Distance from Jupiter, and tides"
        },
        {
          "modality": "text",
          "value": "How often each has been hit"
        }
      ],
      "correctIndex": 2,
      "explanation": "Io sits closest and is held in a resonance that keeps its orbit stretched, so it is kneaded continuously and resurfaces faster than impacts can mark it. Callisto orbits outside that lock, is barely flexed, and keeps a 4.5-billion-year-old face. Both were hit at similar rates.",
      "source": {
        "label": "NASA Science — Callisto",
        "url": "https://science.nasa.gov/jupiter/moons/callisto/"
      },
      "tags": [
        "l06p3",
        "galilean-moons",
        "callisto"
      ],
      "uid": "iwqnp71uzl6vz"
    },
    {
      "id": "ast-c-io-moon",
      "shape": "concept",
      "conceptKind": "thing",
      "name": "Io",
      "clues": [
        "The innermost of the four large moons Galileo found beside Jupiter, only a little larger than Earth's Moon.",
        "It sits deepest in Jupiter's radiation belts and feeds a doughnut of sulphur and oxygen ions that circles the whole planet.",
        "Over 400 active volcanoes and sulfur plumes about 500 km high; eruptions resurface it faster than impacts can scar it, leaving it nearly uncratered."
      ],
      "source": {
        "label": "NASA Science — Io",
        "url": "https://science.nasa.gov/jupiter/moons/io/"
      },
      "tags": [
        "l06p3",
        "galilean-moons",
        "io"
      ],
      "uid": "zokxw49un818"
    },
    {
      "id": "ast-c-europa-moon",
      "shape": "concept",
      "conceptKind": "thing",
      "name": "Europa",
      "clues": [
        "Slightly smaller than Earth's Moon, second out from Jupiter among the four large ones, with a surface near minus 160 °C.",
        "Its outer crust of solid ice is estimated at roughly 10 to 30 km thick — a range wide enough that a spacecraft had to be sent to narrow it.",
        "Under that ice it is thought to hide a saltwater ocean holding about twice as much water as all of Earth's oceans combined."
      ],
      "source": {
        "label": "NASA Science — Europa",
        "url": "https://science.nasa.gov/jupiter/moons/europa/"
      },
      "tags": [
        "l06p3",
        "galilean-moons",
        "europa"
      ],
      "uid": "yyd3dc126f9rs"
    },
    {
      "id": "ast-c-ganymede-moon",
      "shape": "concept",
      "conceptKind": "thing",
      "name": "Ganymede",
      "clues": [
        "The largest of the four moons Galileo found, about 5,262 km across — wider than the planet Mercury.",
        "It outsizes that planet yet holds only about 45 percent of its mass, because it is largely ice and rock rather than metal.",
        "It is the only moon known to generate a magnetic field of its own, something usually found on planets."
      ],
      "source": {
        "label": "NASA Science — Ganymede",
        "url": "https://science.nasa.gov/jupiter/moons/ganymede/"
      },
      "tags": [
        "l06p3",
        "galilean-moons",
        "ganymede"
      ],
      "uid": "yje4cawnnkq0"
    },
    {
      "id": "ast-c-callisto-moon",
      "shape": "concept",
      "conceptKind": "thing",
      "name": "Callisto",
      "clues": [
        "The outermost and least heated of the four large moons, taking about 16.7 days to circle Jupiter — outside the orbital lock that binds the other three.",
        "Its terrain is around 4.5 billion years old, because nothing out there ever resurfaced anything.",
        "The most heavily cratered object in the Solar System, with crater density near saturation: a new impact tends to erase an older one."
      ],
      "source": {
        "label": "NASA Science — Callisto",
        "url": "https://science.nasa.gov/jupiter/moons/callisto/"
      },
      "tags": [
        "l06p3",
        "galilean-moons",
        "callisto"
      ],
      "uid": "16278h9fhszbt"
    },
    {
      "id": "ast-c-europa-clipper-mission",
      "shape": "concept",
      "conceptKind": "thing",
      "name": "Europa Clipper",
      "clues": [
        "It left Earth on 14 October 2024 and is not due to arrive at Jupiter until April 2030.",
        "It will orbit Jupiter rather than the moon it studies, which keeps it clear of the worst radiation.",
        "The plan is 49 close flybys of one ice-covered moon, to test whether that moon could support life; it does not land and it does not drill."
      ],
      "source": {
        "label": "NASA Science — Europa Clipper",
        "url": "https://science.nasa.gov/mission/europa-clipper/"
      },
      "tags": [
        "l06p3",
        "galilean-moons",
        "missions"
      ],
      "uid": "l7zkbm1x8udko"
    },
    {
      "id": "ast-c-sidereus-nuncius",
      "shape": "concept",
      "conceptKind": "thing",
      "name": "Sidereus Nuncius",
      "clues": [
        "Not a world at all but a document, rushed into print in March 1610, two months after the nights it describes.",
        "Its author had improved a homemade telescope, and what he reported seeing beside the largest planet is why his name is attached to four moons.",
        "Direct evidence against an Earth-centred cosmos, in print and circulating within weeks — which is what made it impossible to ignore."
      ],
      "source": {
        "label": "NASA — 415 Years Ago: Astronomer Galileo Discovers Jupiter's Moons",
        "url": "https://www.nasa.gov/general/415-years-ago-astronomer-galileo-discovers-jupiters-moons"
      },
      "tags": [
        "l06p3",
        "galilean-moons",
        "history"
      ],
      "uid": "1rbzelxblj0jt"
    },
    {
      "id": "tfr-ast-d-tidal-heating",
      "shape": "trueFalse",
      "derivedFrom": "ast-d-tidal-heating",
      "statement": "Tidal heating — warmth made inside a body by the flexing of a stretched orbit, rather than by sunlight or by radioactive decay.",
      "isTrue": true,
      "why": "Differentiated means melted early enough that dense metal sank and light rock floated, leaving a body sorted into crust, mantle and core. Tidal heating says where a body's warmth comes from: heat made inside it by the flexing of a stretched orbit, rather than by sunlight or radioactive decay.",
      "source": {
        "label": "NASA Science — Io",
        "url": "https://science.nasa.gov/jupiter/moons/io/"
      },
      "tags": [
        "l06p3",
        "galilean-moons",
        "heating",
        "derived"
      ],
      "uid": "exwuifz0tbqf"
    },
    {
      "id": "ast-f-saturn-lighter-than-water",
      "shape": "fact",
      "title": "Lighter Than Water",
      "body": "Saturn's mean density is **0.6871 g/cm³** — about 30 percent below liquid water, and the only planet in the Solar System under it. The planet carries **95 times Earth's mass** spread through about **760 times Earth's volume**, because **hydrogen and helium**, the two lightest elements, spread that mass through an enormous volume. It is not a bathtub prediction: Saturn's own deep interior is compressed far past the density of water.",
      "factVariant": "image-heavy",
      "imageCaption": "The only planet whose average density comes in below water's.",
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "planet bulk density comparison chart with the density of water marked",
        "imagePrompt": "Flat vector bar chart of the eight planets' mean densities in g/cm3 with a horizontal reference line at 1.0 for water, Saturn's bar alone falling below it.",
        "alt": "Chart of planetary bulk densities with a line at the density of water, and Saturn the only planet below it",
        "depictable": true,
        "allowGenerated": true
      },
      "source": {
        "label": "JPL Solar System Dynamics — Planetary Physical Parameters",
        "url": "https://ssd.jpl.nasa.gov/planets/phys_par.html"
      },
      "tags": [
        "l07p1",
        "saturn",
        "density"
      ],
      "uid": "12dp2sj1dnb9s7"
    },
    {
      "id": "ast-f-saturn-no-surface",
      "shape": "fact",
      "title": "No Ground To Land On",
      "body": "Saturn has **no true surface**. The atmosphere thickens downward into liquid with no sharp boundary, then into a shell of **liquid metallic hydrogen** — which NASA's interior model credits with generating the magnetic field — wrapped around a dense core of heavy elements. There is no hidden rocky floor waiting under the clouds for a probe to stand on.",
      "source": {
        "label": "NASA Science — Saturn Facts",
        "url": "https://science.nasa.gov/saturn/facts/"
      },
      "tags": [
        "l07p1",
        "saturn",
        "interior"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Saturn full disc Cassini portrait",
        "entityTerm": "Saturn",
        "imagePrompt": "A full-disc portrait of Saturn with its rings, showing the planet's subtle cream and ochre banding against black space.",
        "alt": "Saturn's full disc and rings — soft banded cloud that thickens downward into liquid with no ground anywhere",
        "depictable": true,
        "credit": "Unsplash · NASA Hubble Space Telescope · Unsplash License",
        "creditUrl": "https://unsplash.com/photos/saturn-with-a-ring-around-it-in-the-dark-sky-HGjLiyLE8Uo",
        "subject": "clean, well-composed natural-color photograph of Saturn's full disc and rings, soft muted pastel cloud banding, centered and symmetric — matches the card exactly",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-saturn-no-surface.webp"
      },
      "uid": "mur60egotlfk"
    },
    {
      "id": "ast-f-saturn-hexagon",
      "shape": "fact",
      "title": "A Six-Sided Jet Stream",
      "body": "A **hexagon** about **30,000 km** across sits over Saturn's north pole, with winds near **200 miles per hour** and a rotating storm at its centre. It is not an object and not a rendering artefact but a fast river of air whose wave pattern closes into six sides — and it has held that shape for decades. JPL notes there is no weather feature consistently like it anywhere else.",
      "factVariant": "image-heavy",
      "imageCaption": "A natural standing wave in a jet stream, not a shape anyone painted on.",
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Saturn north polar hexagon Cassini image",
        "entityTerm": "Saturn",
        "imagePrompt": "A polar-projection spacecraft image of Saturn's north pole showing the sharply hexagonal jet stream boundary with a circular storm at its centre.",
        "alt": "A monochrome Cassini spacecraft photograph of Saturn seen from above its north pole, with the rings arcing across the top of the frame and the hexagonal jet stream clearly outlined around the pole…",
        "depictable": true,
        "credit": "NASA/JPL-Caltech/Space Science Institute",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:PIA18274-Saturn-NorthPolarHexagon-Cassini-20140402.jpg",
        "subject": "A monochrome Cassini spacecraft photograph of Saturn seen from above its north pole, with the rings arcing across the top of the frame and the hexagonal jet stream clearly outlined around the pole with a small vortex at its centre (NASA image PIA18274, 2 April 2014).",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-saturn-hexagon.webp"
      },
      "source": {
        "label": "JPL — NASA's Cassini Spacecraft Obtains Best Views of Saturn Hexagon",
        "url": "https://www.jpl.nasa.gov/news/nasas-cassini-spacecraft-obtains-best-views-of-saturn-hexagon/"
      },
      "tags": [
        "l07p1",
        "saturn",
        "atmosphere"
      ],
      "uid": "1wsz42g1uufvn0"
    },
    {
      "id": "ast-f-saturn-ring-clock",
      "shape": "fact",
      "title": "Telling Time By Rings",
      "body": "With no surface to time, and a magnetic field almost perfectly aligned with its spin axis, Saturn defeated the usual method of watching a tilted field wobble round. Cassini data showed vibrations inside the planet driving waves in the **C ring**; reading those back gives a day of **10 hours 33 minutes 38 seconds**, several minutes shorter than the Voyager-era radio estimate. JPL's table still carries the old figure.",
      "source": {
        "label": "NASA Science — Scientists Finally Know What Time It Is on Saturn",
        "url": "https://science.nasa.gov/solar-system/scientists-finally-know-what-time-it-is-on-saturn/"
      },
      "tags": [
        "l07p1",
        "saturn",
        "rotation"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Saturn C ring density waves",
        "imagePrompt": "Documentary-style photograph: Fine spiral density waves rippling through Saturn's C ring, the internal-oscillation signal used to measure the planet's rotation. Natural light, no readable text, no logos, no watermarks.",
        "alt": "Fine spiral density waves rippling through Saturn's C ring, the internal-oscillation signal used to measure the planet's rotation"
      },
      "uid": "mpxo9uj28m0a"
    },
    {
      "id": "ast-d-oblateness",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Oblateness"
      },
      "definition": {
        "modality": "text",
        "value": "The equatorial bulge a spinning world takes on, given as the fraction of the equatorial radius by which it exceeds the polar one"
      },
      "source": {
        "label": "Las Cumbres Observatory — Saturn",
        "url": "https://lco.global/spacebook/solar-system/saturn/"
      },
      "tags": [
        "l07p1",
        "saturn",
        "shape"
      ],
      "uid": "1fkxw4h1pmtkev"
    },
    {
      "id": "ast-p-saturn-from-the-sun",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Saturn from the Sun"
      },
      "sideB": {
        "modality": "text",
        "value": "9.5 astronomical units — nearly twice as far out as Jupiter",
        "short": "9.5 astronomical units"
      },
      "source": {
        "label": "NASA Science — Saturn Facts",
        "url": "https://science.nasa.gov/saturn/facts/"
      },
      "tags": [
        "l07p1",
        "saturn",
        "orbit"
      ],
      "uid": "1o8p5c1hvoits"
    },
    {
      "id": "ast-p-saturn-axial-tilt",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Saturn's axial tilt"
      },
      "sideB": {
        "modality": "text",
        "value": "26.73 degrees, giving seasons about seven Earth years long",
        "short": "26.73 degrees"
      },
      "source": {
        "label": "NASA Science — Saturn Facts",
        "url": "https://science.nasa.gov/saturn/facts/"
      },
      "tags": [
        "l07p1",
        "saturn",
        "seasons"
      ],
      "uid": "4e3cb8h5bpo2"
    },
    {
      "id": "ast-q-saturn-day-not-year",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Saturn takes 29.4 Earth years to circle the Sun. How long does it take to spin once?"
      },
      "options": [
        {
          "modality": "text",
          "value": "About 29 Earth days"
        },
        {
          "modality": "text",
          "value": "About 10.7 hours"
        },
        {
          "modality": "text",
          "value": "About 24 hours"
        },
        {
          "modality": "text",
          "value": "About 10.7 Earth days"
        }
      ],
      "correctIndex": 1,
      "explanation": "Ring seismology gives 10 h 33 m and the older Voyager figure 10 h 39 m; both round to about 10.7 hours. The 24-hour option is Earth's, borrowed by habit; 10.7 Earth days and 29 Earth days both assume a long year forces a long day. The two are unrelated.",
      "source": {
        "label": "NASA Science — Saturn Facts",
        "url": "https://science.nasa.gov/saturn/facts/"
      },
      "tags": [
        "l07p1",
        "saturn",
        "rotation"
      ],
      "uid": "dl3sq61r3mg4w"
    },
    {
      "id": "ast-q-saturn-ringed-worlds",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "All four giant planets have rings. Why does only Saturn's system stand out?"
      },
      "options": [
        {
          "modality": "text",
          "value": "The other three formed far later"
        },
        {
          "modality": "text",
          "value": "Its rings alone are solid"
        },
        {
          "modality": "text",
          "value": "Its rings reflect far more light"
        },
        {
          "modality": "text",
          "value": "The others orbit edge-on to us"
        }
      ],
      "correctIndex": 2,
      "explanation": "Saturn's rings return about 60 percent of the light that hits them; Uranus's and Neptune's return about 5 percent, which is why they went unseen until the 1970s and 80s. All four systems are particles rather than solid sheets, all four are ancient, and none is hidden by its viewing angle.",
      "source": {
        "label": "OpenStax Astronomy (SUNY) — Planetary Rings",
        "url": "https://courses.lumenlearning.com/suny-astronomy/chapter/planetary-rings/"
      },
      "tags": [
        "l07p1",
        "saturn",
        "rings"
      ],
      "uid": "1lshyf81ckc69a"
    },
    {
      "id": "czr-ast-d-oblateness",
      "shape": "cloze",
      "derivedFrom": "ast-d-oblateness",
      "template": "___ — The equatorial bulge a spinning world takes on, given as the fraction of the equatorial radius by which it exceeds the polar one",
      "answer": "Oblateness",
      "distractors": [
        "Airmass",
        "Apparent magnitude",
        "Solar mass"
      ],
      "explanation": "Oblateness is the equatorial bulge a spinning world takes on, given as the fraction of the equatorial radius by which it exceeds the polar one. Airmass, the closest of the alternatives, is how much atmosphere a beam crosses on its way down.",
      "source": {
        "label": "Las Cumbres Observatory — Saturn",
        "url": "https://lco.global/spacebook/solar-system/saturn/"
      },
      "tags": [
        "l07p1",
        "saturn",
        "shape",
        "derived"
      ],
      "uid": "2mopvk1yuub7o"
    },
    {
      "id": "tfr-ast-d-oblateness",
      "shape": "trueFalse",
      "derivedFrom": "ast-d-oblateness",
      "statement": "Oblateness — the equatorial bulge a spinning world takes on, given as the fraction of the equatorial radius by which it exceeds the polar one.",
      "isTrue": true,
      "why": "The frost line is the distance from a young star beyond which water stops being vapour and freezes into solid grains, which is why the giant planets could form out there. Oblateness is a shape rather than a distance: the equatorial bulge a spinning world takes on.",
      "source": {
        "label": "Las Cumbres Observatory — Saturn",
        "url": "https://lco.global/spacebook/solar-system/saturn/"
      },
      "tags": [
        "l07p1",
        "saturn",
        "shape",
        "derived"
      ],
      "uid": "17tlchrrot2wp"
    },
    {
      "id": "ast-f-saturn-rings-are-ice",
      "shape": "fact",
      "title": "Billions Of Separate Orbits",
      "body": "Saturn's rings are almost entirely **water ice** — billions of separate chunks, from grains smaller than sand up to boulders the size of houses. **Nothing is joined**: every particle keeps its own orbit around the planet. That near-purity is why the rings throw back roughly **60 percent** of the light that hits them, against about 5 percent for the sooty rings of Uranus and Neptune.",
      "factVariant": "image-heavy",
      "imageCaption": "Not a disc and not a dust band — countless icy bodies, each on its own path.",
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Saturn ring particles close-up Cassini",
        "entityTerm": "Rings of Saturn",
        "imagePrompt": "A very close spacecraft image of Saturn's rings resolved into hundreds of fine concentric ringlets of bright water ice.",
        "alt": "A Cassini spacecraft close-up (NASA/JPL/SSI) of the outer edge of Saturn's B ring: fine diagonal bands of ring material with a mottled, clumpy texture, a wide dark gap, and a thin bright ringlet…",
        "depictable": true,
        "credit": "Wikimedia Commons · RidingWithRobots · CC BY-SA 2.0",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:Rings_Close-Up_(2652610211).jpg",
        "subject": "A Cassini spacecraft close-up (NASA/JPL/SSI) of the outer edge of Saturn's B ring: fine diagonal bands of ring material with a mottled, clumpy texture, a wide dark gap, and a thin bright ringlet running through it, in monochrome.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-saturn-rings-are-ice.webp"
      },
      "source": {
        "label": "NASA Science — Cassini: Saturn Rings",
        "url": "https://science.nasa.gov/mission/cassini/science/rings/"
      },
      "tags": [
        "l07p2",
        "saturn",
        "rings"
      ],
      "uid": "xgoixb1c1yppt"
    },
    {
      "id": "ast-f-saturn-rings-thickness",
      "shape": "fact",
      "title": "Ten Metres Of Ice",
      "body": "The ring system reaches about **282,000 km** out from Saturn while the main rings are of the order of **10 metres** thick — a sheet tens of millions of times wider than it is deep. Scaled to a sheet of paper 0.1 mm thick, it would run roughly 3 km from the middle out to the rim. Published figures disagree — NASA about 10 m, OpenStax an average of 20 m, NASA's own rings page under 100 m in most places — so hold the order of magnitude, not a value.",
      "source": {
        "label": "NASA Science — Saturn Facts",
        "url": "https://science.nasa.gov/saturn/facts/"
      },
      "tags": [
        "l07p2",
        "saturn",
        "rings"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Saturn rings seen edge-on ring plane crossing nearly disappearing",
        "entityTerm": "Rings of Saturn",
        "imagePrompt": "A photograph of Saturn with the rings almost exactly edge-on, reduced to a razor-thin bright line crossing the planet's disc.",
        "alt": "A computer-rendered view of Saturn — a pale cream-and-tan banded gas giant in the upper left, half in shadow — with its broad, flat ring system sweeping down and to the right at an oblique angle…",
        "depictable": true,
        "subject": "A computer-rendered view of Saturn — a pale cream-and-tan banded gas giant in the upper left, half in shadow — with its broad, flat ring system sweeping down and to the right at an oblique angle against a starfield; the rings read as a paper-thin sheet with fine divisions, but are not seen edge-on.",
        "credit": "Pexels · Stunning visual of Saturn and its iconic rings against the backdrop of space.",
        "creditUrl": "https://www.pexels.com/photo/planet-with-rings-in-space-12491661/",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-saturn-rings-thickness.webp"
      },
      "uid": "o3e2jfzx32ib"
    },
    {
      "id": "ast-f-saturn-rings-lettering",
      "shape": "fact",
      "title": "Lettered By Discovery",
      "body": "The **seven main rings** carry letters in the order they were found, not by position, which is why the sequence looks scrambled: outward from Saturn they run **D, C, B, A, F, G and E**. A, B and C are the bright ones. The **Cassini Division**, about **4,700 km** wide, is the largest gap, separating B from A — not an empty vacuum, though what fills it is not settled here — and named for the 17th-century astronomer who first glimpsed it in 1675, not for the spacecraft.",
      "source": {
        "label": "NASA Science — Saturn's Rings",
        "url": "https://science.nasa.gov/resource/saturns-rings-2/"
      },
      "tags": [
        "l07p2",
        "saturn",
        "rings"
      ],
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "Saturn ring system labelled diagram D C B A F G E rings Cassini Division",
        "imagePrompt": "Flat vector cross-section diagram of Saturn's ring system from the planet outward, each main ring labelled with its discovery letter and the 4,700 km Cassini Division marked between B and A.",
        "alt": "Labelled diagram of Saturn's rings running outward D, C, B, A, F, G, E, with the Cassini Division marked between B and A",
        "depictable": true,
        "allowGenerated": true
      },
      "uid": "1by9pj91w3ev5b"
    },
    {
      "id": "ast-f-saturn-ring-age-argument",
      "shape": "fact",
      "title": "Younger Than The Planet?",
      "body": "Cassini's **Grand Finale** weighed the rings at about **1.54 × 10¹⁹ kg**, roughly 0.41 times the mass of the small moon Mimas. Interplanetary dust darkens ice at a roughly known rate, so rings this bright and this light cannot have sat there for 4.5 billion years: the modelled age is **10 to 100 million years**. Crida and colleagues argued in 2019 that some unknown process may be *cleaning* the rings, making genuinely ancient ones look young. Treat the age as an inference, not a measurement.",
      "source": {
        "label": "JPL — NASA's Cassini Data Show Saturn's Rings Relatively New",
        "url": "https://www.jpl.nasa.gov/news/nasas-cassini-data-show-saturns-rings-relatively-new/"
      },
      "tags": [
        "l07p2",
        "saturn",
        "rings"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Saturn rings backlit by the Sun Cassini image",
        "entityTerm": "Rings of Saturn",
        "imagePrompt": "A spacecraft image taken from Saturn's night side with the Sun behind the planet, the rings glowing brightly by forward-scattered light.",
        "alt": "Saturn's rings lit from behind, still bright and clean enough that they cannot be as old as the planet",
        "depictable": true,
        "credit": "NASA / JPL-Caltech / Space Science Institute · Public domain",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:PIA17172_Saturn_eclipse_mosaic_bright_crop.jpg",
        "subject": "Same 'Saturn eclipse mosaic' (PIA17172) as index 0, but the direct Wikimedia Commons file — Saturn backlit by the Sun, full ring system glowing bright and clean, credited to NASA/JPL-Caltech/Space Science Institute.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-saturn-ring-age-argument.webp"
      },
      "uid": "vjunjj1j023ft"
    },
    {
      "id": "ast-d-roche-limit",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Roche limit"
      },
      "definition": {
        "modality": "text",
        "value": "The distance from a planet inside which tidal forces tear a large body apart and stop loose particles from gathering into one"
      },
      "source": {
        "label": "NASA Science — Cassini FAQ",
        "url": "https://science.nasa.gov/mission/cassini/faq/"
      },
      "tags": [
        "l07p2",
        "saturn",
        "rings"
      ],
      "uid": "1ml81oh13n2ghj"
    },
    {
      "id": "ast-p-cassini-grand-finale",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Cassini's Grand Finale"
      },
      "sideB": {
        "modality": "text",
        "value": "22 orbits threaded between the cloud tops and the innermost ring",
        "short": "22 orbits inside the rings"
      },
      "source": {
        "label": "NASA Science — Cassini's Grand Finale: Overview",
        "url": "https://science.nasa.gov/mission/cassini/grand-finale/overview/"
      },
      "tags": [
        "l07p2",
        "cassini",
        "rings"
      ],
      "uid": "dzngwi61bbfi"
    },
    {
      "id": "ast-p-saturn-ring-rain",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Ring rain"
      },
      "sideB": {
        "modality": "text",
        "value": "Charged ice grains spiralling down into the upper atmosphere",
        "short": "Charged ice grains falling into Saturn"
      },
      "source": {
        "label": "NASA Science — NASA Research Reveals Saturn is Losing Its Rings at 'Worst-Case-Scenario' Rate",
        "url": "https://science.nasa.gov/solar-system/nasa-research-reveals-saturn-is-losing-its-rings-at-worst-case-scenario-rate"
      },
      "tags": [
        "l07p2",
        "saturn",
        "rings"
      ],
      "uid": "dwzzqrnzuir3"
    },
    {
      "id": "ast-q-encke-gap-held-open",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "What accounts for the Encke Gap in the A ring?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Material never gathered there"
        },
        {
          "modality": "text",
          "value": "Sunlight pushing ice grains out"
        },
        {
          "modality": "text",
          "value": "Saturn's magnetic field"
        },
        {
          "modality": "text",
          "value": "A small moon orbiting inside it"
        }
      ],
      "correctIndex": 3,
      "explanation": "Pan — mean radius about 14 km — orbits inside the Encke Gap and holds it open. Gaps like this are actively cleared, not places where material never gathered, and NASA credits the moon, not sunlight pressure or Saturn's magnetic field, with the work.",
      "source": {
        "label": "NASA Science — Pan",
        "url": "https://science.nasa.gov/saturn/moons/pan/"
      },
      "tags": [
        "l07p2",
        "saturn",
        "rings"
      ],
      "uid": "1jfxc0y1s9qjfw"
    },
    {
      "id": "ast-q-saturn-rings-composition",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "What are Saturn's rings actually made of?"
      },
      "options": [
        {
          "modality": "text",
          "value": "One solid frozen sheet"
        },
        {
          "modality": "text",
          "value": "Countless separate ice chunks"
        },
        {
          "modality": "text",
          "value": "A continuous band of fine dust"
        },
        {
          "modality": "text",
          "value": "Rock ground down by impacts"
        }
      ],
      "correctIndex": 1,
      "explanation": "NASA describes them as almost completely chunks of water ice, from sand grains to house-sized boulders, each on its own orbit. A solid frozen sheet and a continuous dust band both deny that independence; ground-down rock misses that the material is overwhelmingly ice.",
      "source": {
        "label": "NASA Science — Cassini: Saturn Rings",
        "url": "https://science.nasa.gov/mission/cassini/science/rings/"
      },
      "tags": [
        "l07p2",
        "saturn",
        "rings"
      ],
      "uid": "flvlinkd0lhd"
    },
    {
      "id": "czr-ast-d-roche-limit",
      "shape": "cloze",
      "derivedFrom": "ast-d-roche-limit",
      "template": "___ — The distance from a planet inside which tidal forces tear a large body apart and stop loose particles from gathering into one",
      "answer": "Roche limit",
      "distractors": [
        "Airmass",
        "Apparent magnitude",
        "Solar mass"
      ],
      "explanation": "Roche limit is the distance from a planet inside which tidal forces tear a large body apart and stop loose particles from gathering into one. Airmass, the closest of the alternatives, is how much atmosphere a beam crosses on its way down.",
      "source": {
        "label": "NASA Science — Cassini FAQ",
        "url": "https://science.nasa.gov/mission/cassini/faq/"
      },
      "tags": [
        "l07p2",
        "saturn",
        "rings",
        "derived"
      ],
      "uid": "o3s57a1hbs5f2"
    },
    {
      "id": "tfr-ast-d-roche-limit",
      "shape": "trueFalse",
      "derivedFrom": "ast-d-roche-limit",
      "statement": "Roche limit — the distance from a young star beyond which water stops being vapour and freezes into solid grains.",
      "isTrue": false,
      "why": "The frost line is the distance from a young star beyond which water stops being vapour and freezes into solid grains. The Roche limit is measured from a planet instead: the distance inside which tidal forces tear a large body apart and stop loose particles from gathering into one.",
      "source": {
        "label": "NASA Science — Cassini FAQ",
        "url": "https://science.nasa.gov/mission/cassini/faq/"
      },
      "tags": [
        "l07p2",
        "saturn",
        "rings",
        "derived"
      ],
      "whyOptions": [
        "Airmass",
        "Apparent magnitude",
        "Frost line"
      ],
      "whyCorrectIndex": 2,
      "uid": "1q1fn3i8spdrq"
    },
    {
      "id": "ast-f-saturn-moon-count-dated",
      "shape": "fact",
      "title": "A Count With A Date",
      "body": "NASA records **274 confirmed moons** as of **March 2025**, after the Minor Planet Center recognised 128 in one announcement that month; 11 more followed in March 2026. Date the figure whenever you use it — it tracks telescope sensitivity and confirmation backlog, not Saturn, and published counts disagree because their definitions differ. Almost all are irregular fragments a few kilometres across.",
      "source": {
        "label": "NASA Science — Saturn Facts",
        "url": "https://science.nasa.gov/saturn/facts/"
      },
      "tags": [
        "l07p3",
        "saturn",
        "moons"
      ],
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "Saturn confirmed moon count over time chart",
        "imagePrompt": "Flat vector step chart of Saturn's confirmed moon count against year, rising in jumps and marked at the 2025 and 2026 announcements.",
        "alt": "NASA/Cassini mosaic of Saturn viewed from above its north pole: the cream-and-tan planet with the hexagonal polar storm visible at centre, encircled by its full ring system, with the planet's…",
        "depictable": true,
        "allowGenerated": true,
        "subject": "NASA/Cassini mosaic of Saturn viewed from above its north pole: the cream-and-tan planet with the hexagonal polar storm visible at centre, encircled by its full ring system, with the planet's shadow falling across the rings to the left, on a black sky.",
        "credit": "Wikimedia Commons · Public domain",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:Top_view_of_the_rings_of_Saturn_by_Cassini_-_October_10,_2013.jpg",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-saturn-moon-count-dated.webp"
      },
      "uid": "1en1qm51w09dcv"
    },
    {
      "id": "ast-f-saturn-moon-size-ladder",
      "shape": "fact",
      "title": "One Rung Above The Rest",
      "body": "Saturn itself is about **60,250 km** in radius. Its large round moons line up by mean radius: **Titan 2,575 km**, then Rhea 764, Iapetus 734, Dione 561, Tethys 531, Enceladus 252 and Mimas 198. Cube those and Titan holds roughly **14 times the volume** of the other six put together — and Titan is wider than the planet Mercury. It is not merely first in the list; it is in a different class.",
      "factVariant": "image-heavy",
      "imageCaption": "One moon bigger than Mercury, and six between a tenth and a third of its width.",
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "Saturn major moons size comparison chart Titan Rhea Iapetus Dione Tethys Enceladus Mimas",
        "imagePrompt": "Flat scale diagram of Saturn's seven large round moons drawn to true relative size in a row, Titan dwarfing the rest, with Mercury outlined for comparison.",
        "alt": "Size ladder of Saturn's round moons: Titan far larger than the other six put together, and wider than Mercury",
        "depictable": true,
        "allowGenerated": true
      },
      "source": {
        "label": "JPL Solar System Dynamics — Planetary Satellite Physical Parameters",
        "url": "https://ssd.jpl.nasa.gov/sats/phys_par/"
      },
      "tags": [
        "l07p3",
        "saturn",
        "moons"
      ],
      "uid": "1rnnizr1gojlnn"
    },
    {
      "id": "ast-f-saturn-moons-found-from-earth",
      "shape": "fact",
      "title": "Found From The Ground",
      "body": "Every one of Saturn's nine best-known moons was found from Earth, the first of them three and a half centuries before a spacecraft arrived. Christiaan **Huygens** found Titan in **1655**; Giovanni **Cassini** found Iapetus, Rhea, Tethys and Dione between 1671 and 1684; William Herschel added Mimas and Enceladus in 1789; Hyperion came in 1848, and Phoebe — the first moon anywhere found by photography — in 1898-99.",
      "source": {
        "label": "NASA Science — Titan Facts",
        "url": "https://science.nasa.gov/saturn/moons/titan/facts/"
      },
      "tags": [
        "l07p3",
        "saturn",
        "discovery"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Titan hazy orange globe Cassini image",
        "entityTerm": "Titan (moon)",
        "imagePrompt": "A spacecraft image of Titan as a smooth, uniformly orange hazy globe with a detached upper haze layer visible at the limb.",
        "alt": "A monochrome, ground-based amateur telescope photograph of the planet Saturn: a soft grey disc with its rings tilted open, the Cassini Division faintly visible, small in an otherwise black frame.",
        "depictable": true,
        "subject": "A monochrome, ground-based amateur telescope photograph of the planet Saturn: a soft grey disc with its rings tilted open, the Cassini Division faintly visible, small in an otherwise black frame. It shows Saturn, not Titan; a faint point below the planet may be a moon but cannot be identified.",
        "credit": "Pexels · A captivating black and white photograph of Saturn showcasing its iconic rings.",
        "creditUrl": "https://www.pexels.com/photo/view-of-saturn-13371408/",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-saturn-moons-found-from-earth.webp"
      },
      "uid": "1ivvwfaz5tg9k"
    },
    {
      "id": "ast-f-cassini-deliberate-ending",
      "shape": "fact",
      "title": "The Deliberate Ending",
      "body": "Cassini launched on 15 October 1997, reached Saturn in 2004, and on **15 September 2017** was deliberately flown into the planet. That was not a failure. Rather than risk an uncontrolled crash once the fuel ran out, NASA destroyed the spacecraft in Saturn's atmosphere so it could never contaminate **Enceladus or Titan**. Almost everything here beyond the bare numbers came from those 13 years in orbit.",
      "source": {
        "label": "NASA Science — Cassini mission",
        "url": "https://science.nasa.gov/mission/cassini/"
      },
      "tags": [
        "l07p3",
        "cassini",
        "moons"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Cassini spacecraft clean room",
        "imagePrompt": "Documentary-style photograph: The Cassini spacecraft during assembly and testing in a NASA clean room before its 1997 launch. Natural light, no readable text, no logos, no watermarks.",
        "alt": "The Cassini spacecraft during assembly and testing in a NASA clean room before its 1997 launch"
      },
      "uid": "16hhqjl1xowsb9"
    },
    {
      "id": "ast-d-tiger-stripes",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Tiger stripes"
      },
      "definition": {
        "modality": "text",
        "value": "The four roughly 135-km fractures crossing Enceladus's south pole — the warmest ground on the moon and the source of every jet in its plume"
      },
      "source": {
        "label": "NASA Science — Cassini at Enceladus",
        "url": "https://science.nasa.gov/mission/cassini/science/enceladus/"
      },
      "tags": [
        "l07p3",
        "enceladus",
        "moons"
      ],
      "uid": "1oy9m3wlvzso4"
    },
    {
      "id": "ast-c-moon-titan",
      "shape": "concept",
      "conceptKind": "thing",
      "name": "Titan",
      "clues": [
        "The second-largest moon in the Solar System, about 2,575 km in radius — roughly 14 times the volume of Saturn's six other round moons put together.",
        "It is the only moon with a substantial atmosphere — about 95 percent nitrogen — and at ground level that air presses about half again as hard as Earth's.",
        "Lakes and seas of methane and ethane stand on its surface, and ESA's Huygens probe landed there on 14 January 2005, the most distant landing ever achieved."
      ],
      "source": {
        "label": "NASA Science — Titan Facts",
        "url": "https://science.nasa.gov/saturn/moons/titan/facts/"
      },
      "tags": [
        "l07p3",
        "saturn",
        "moons"
      ],
      "uid": "11ek3agqsfsj0"
    },
    {
      "id": "ast-c-moon-enceladus",
      "shape": "concept",
      "conceptKind": "thing",
      "name": "Enceladus",
      "clues": [
        "Only about 500 km across, and the most reflective body in the Solar System — most of what it throws into space falls back and repaints the surface with clean ice.",
        "Water vapour, ice grains, salts and organics erupt from four fractures across its south pole, fed by a global ocean beneath the crust.",
        "Silica nanograins in that plume imply hydrothermal vents on the ocean floor, and the fraction of ice that escapes builds Saturn's faint E ring."
      ],
      "source": {
        "label": "NASA Science — Enceladus",
        "url": "https://science.nasa.gov/saturn/moons/enceladus/"
      },
      "tags": [
        "l07p3",
        "saturn",
        "moons"
      ],
      "uid": "b0tk8014x1kj0"
    },
    {
      "id": "ast-c-moon-mimas",
      "shape": "concept",
      "conceptKind": "thing",
      "name": "Mimas",
      "clues": [
        "Grey, ancient and battered, this small inner moon is about 394 km across — a near twin in size of its far brighter, far more active neighbour.",
        "One crater, Herschel, is 130 km wide — a third of the whole moon — with outer walls about 5 km high.",
        "That crater still carries a central peak standing 6 km high, which is why the moon is so often compared to the Death Star."
      ],
      "source": {
        "label": "NASA Science — Mimas",
        "url": "https://science.nasa.gov/saturn/moons/mimas/"
      },
      "tags": [
        "l07p3",
        "saturn",
        "moons"
      ],
      "uid": "lhzzh398cz6f"
    },
    {
      "id": "ast-c-moon-tethys",
      "shape": "concept",
      "conceptKind": "thing",
      "name": "Tethys",
      "clues": [
        "About 1,060 km across and almost pure water ice: at 0.98 times the density of water it is the only one of Saturn's seven large round moons that comes in under that mark.",
        "Its 400-km impact scar, Odysseus, has collapsed into a shallow basin with no standing central peak.",
        "Ithaca Chasma, a canyon roughly 2,000 km long and about 100 km wide, runs most of the way round the globe."
      ],
      "source": {
        "label": "NASA Science — Tethys",
        "url": "https://science.nasa.gov/saturn/moons/tethys/"
      },
      "tags": [
        "l07p3",
        "saturn",
        "moons"
      ],
      "uid": "180521uqfgzx6"
    },
    {
      "id": "ast-c-moon-dione",
      "shape": "concept",
      "conceptKind": "thing",
      "name": "Dione",
      "clues": [
        "A mid-sized icy moon, mean radius 561 km, with a density of 1.48 times water — proportionally more rock inside than most of Saturn's ice moons.",
        "It orbits between Tethys and Rhea, and the bright fracture network sits on its trailing side while the leading side takes the heavier cratering.",
        "It is the reason Enceladus still has plumes: NASA states it holds Enceladus locked at exactly half its own orbital period, and that repeated 1:2 tug keeps the smaller moon's ocean liquid."
      ],
      "source": {
        "label": "NASA Science — Dione",
        "url": "https://science.nasa.gov/saturn/moons/dione/"
      },
      "tags": [
        "l07p3",
        "saturn",
        "moons"
      ],
      "uid": "1lqhzr5obopah"
    },
    {
      "id": "ast-c-moon-rhea",
      "shape": "concept",
      "conceptKind": "thing",
      "name": "Rhea",
      "clues": [
        "A heavily cratered ice moon, second in size among Saturn's family though still under a third the width of the largest.",
        "Its density of 1.24 times water makes it mostly water ice, with noticeably less rock inside than its neighbour Dione.",
        "In 2010 Cassini captured molecules of an oxygen exosphere here — the first direct capture of oxygen at a world other than Earth."
      ],
      "source": {
        "label": "NASA Science — Rhea",
        "url": "https://science.nasa.gov/saturn/moons/rhea/"
      },
      "tags": [
        "l07p3",
        "saturn",
        "moons"
      ],
      "uid": "hl9tkiymctho"
    },
    {
      "id": "ast-c-moon-iapetus",
      "shape": "concept",
      "conceptKind": "thing",
      "name": "Iapetus",
      "clues": [
        "Mean radius 734 km, the third-largest of Saturn's moons, and the one Giovanni Cassini could see on one side of the planet in 1671 but not on the other.",
        "Its leading hemisphere is as dark as coal, reflecting 3 to 5 percent of the light, while the trailing hemisphere reflects 50 to 60 percent.",
        "A chain of mountains about 10 km high runs along its equator for some 1,300 km, giving it a walnut profile that four competing hypotheses still fail to settle."
      ],
      "source": {
        "label": "NASA Science — Iapetus",
        "url": "https://science.nasa.gov/saturn/moons/iapetus/"
      },
      "tags": [
        "l07p3",
        "saturn",
        "moons"
      ],
      "uid": "lhtcew1pxdjfo"
    },
    {
      "id": "ast-c-moon-phoebe",
      "shape": "concept",
      "conceptKind": "thing",
      "name": "Phoebe",
      "clues": [
        "A small outer moon, mean radius about 106 km, circling Saturn nearly 13 million km out on a steeply tilted orbit.",
        "It travels the wrong way round — backwards relative to Saturn's spin — which is why it is thought to be a captured body rather than a moon that formed here.",
        "Dust shed from it forms a vast faint disc that Spitzer found in infrared in 2009, tilted 27 degrees to the main rings and orbiting backwards with it."
      ],
      "source": {
        "label": "NASA Science — Phoebe",
        "url": "https://science.nasa.gov/saturn/moons/phoebe/"
      },
      "tags": [
        "l07p3",
        "saturn",
        "moons"
      ],
      "uid": "hwpj1f1qll0z9"
    },
    {
      "id": "ast-c-moon-hyperion",
      "shape": "concept",
      "conceptKind": "thing",
      "name": "Hyperion",
      "clues": [
        "A lopsided, irregular lump a few hundred kilometres across and markedly less dense than water — published dimensions disagree across sources.",
        "NASA describes its surface as curiously punched in, like a sponge or a wasp nest — possibly because more than 40 percent of it is empty space.",
        "It tumbles chaotically: its spin axis wobbles so much that its orientation in space cannot be predicted from one week to the next."
      ],
      "source": {
        "label": "NASA Science — Hyperion",
        "url": "https://science.nasa.gov/saturn/moons/hyperion/"
      },
      "tags": [
        "l07p3",
        "saturn",
        "moons"
      ],
      "uid": "1ymcpal18t2a2t"
    },
    {
      "id": "ast-q-titan-standing-seas",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "What fills the standing seas at Titan's poles?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Liquid nitrogen"
        },
        {
          "modality": "text",
          "value": "Molten sulphur brine"
        },
        {
          "modality": "text",
          "value": "Water and ammonia"
        },
        {
          "modality": "text",
          "value": "Methane and ethane"
        }
      ],
      "correctIndex": 3,
      "explanation": "Cassini's radar sounded Ligeia Mare to 160 metres and found it predominantly methane. Nitrogen makes up about 95 percent of Titan's air but stays gaseous; at about −180 °C water, ammonia or not, is rock-hard ice rather than a sea; and no sulphur is involved.",
      "source": {
        "label": "NASA Science — Titan Facts",
        "url": "https://science.nasa.gov/saturn/moons/titan/facts/"
      },
      "tags": [
        "l07p3",
        "titan",
        "moons"
      ],
      "uid": "10h1g4x1dmcdy9"
    },
    {
      "id": "ast-q-enceladus-silica-grains",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "What did silica nanograins in Enceladus's plume point to?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Ice grinding in the fractures"
        },
        {
          "modality": "text",
          "value": "Dust falling in from the E ring"
        },
        {
          "modality": "text",
          "value": "Salt crystals left by the plume"
        },
        {
          "modality": "text",
          "value": "Vents on its ocean floor"
        }
      ],
      "correctIndex": 3,
      "explanation": "Silica nanograins of that size form only where liquid water meets rock above about 90 C, which points to hydrothermal vents on the ocean floor. Grinding ice makes ice, not silica; the E ring is fed BY the plume rather than into it; and salt was a separate detection.",
      "source": {
        "label": "NASA Science — Enceladus",
        "url": "https://science.nasa.gov/saturn/moons/enceladus/"
      },
      "tags": [
        "l07p3",
        "enceladus",
        "moons"
      ],
      "uid": "rpd8u9fe7cw1"
    },
    {
      "id": "tfr-ast-d-tiger-stripes",
      "shape": "trueFalse",
      "derivedFrom": "ast-d-tiger-stripes",
      "statement": "Tiger stripes — the four roughly 135-km fractures crossing Enceladus's south pole.",
      "isTrue": true,
      "why": "A penumbra is the outer part of a shadow, where the light source is partly blocked rather than hidden completely. The tiger stripes are something else entirely: the four roughly 135-km fractures crossing Enceladus's south pole, the vents that feed the moon's plume and, through it, Saturn's E ring.",
      "source": {
        "label": "NASA Science — Cassini at Enceladus",
        "url": "https://science.nasa.gov/mission/cassini/science/enceladus/"
      },
      "tags": [
        "l07p3",
        "enceladus",
        "moons",
        "derived"
      ],
      "uid": "eqebou1jdwu9y"
    },
    {
      "id": "ast-f-ice-giant-not-frozen",
      "shape": "fact",
      "title": "Ices That Are Not Frozen",
      "body": "Jupiter and Saturn are **gas giants**, mostly hydrogen and helium — the same material as the Sun. Uranus and Neptune are **ice giants**: a hot, dense fluid of **water, methane and ammonia** over a small **rocky core**. Those compounds are called ices because out here they are normally frozen, not because they are solid inside the planet.",
      "factVariant": "image-heavy",
      "imageCaption": "The 'ices' in an ice giant are a hot, dense fluid over a rocky core, not solid ice.",
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "ice giant interior cutaway diagram Uranus Neptune water methane ammonia mantle",
        "imagePrompt": "Flat vector cutaway of Uranus and Neptune side by side showing a small rocky core, a thick hot fluid mantle labelled water/methane/ammonia, and a hydrogen-helium envelope above.",
        "alt": "Cutaway diagram of an ice giant: a small rocky core under a hot dense fluid mantle of water, methane and ammonia",
        "depictable": true,
        "allowGenerated": true
      },
      "source": {
        "label": "NASA Science — Planets",
        "url": "https://science.nasa.gov/solar-system/planets/"
      },
      "tags": [
        "l08p1",
        "ice-giants",
        "composition"
      ],
      "uid": "1l0rsz3mhhsu3"
    },
    {
      "id": "ast-f-icegiant-four-earths-wide",
      "shape": "fact",
      "title": "Four Earths Wide",
      "body": "Uranus measures **51,118 km** across at the equator — four times Earth's width, but only about a third of Jupiter's diameter. Neptune measures **49,528 km**, very slightly the smaller of the two. The ice giants are near-twins, within about 3 percent of each other in width, and the two giant classes do not overlap in size at all.",
      "source": {
        "label": "JPL Solar System Dynamics — Planetary Physical Parameters",
        "url": "https://ssd.jpl.nasa.gov/planets/phys_par.html"
      },
      "tags": [
        "l08p1",
        "ice-giants",
        "size"
      ],
      "uid": "wi7zcw1e2qn48"
    },
    {
      "id": "ast-f-neptune-smaller-heavier",
      "shape": "fact",
      "title": "The Smaller, Heavier Twin",
      "body": "Then the ordering flips. Uranus holds **14.5 Earth masses**, Neptune **17.1** — more matter in the smaller ball. What flips it is **bulk density**: Neptune is the densest of the four giants at **1.638 g/cm3**, ahead of Jupiter at 1.326, Uranus at 1.270 and Saturn at 0.687. Note what the ladder does not say — Uranus is not denser than Jupiter despite being icier, because Jupiter's own weight squeezes its hydrogen to a comparable density.",
      "source": {
        "label": "JPL Solar System Dynamics — Planetary Physical Parameters",
        "url": "https://ssd.jpl.nasa.gov/planets/phys_par.html"
      },
      "tags": [
        "l08p1",
        "ice-giants",
        "density"
      ],
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "giant planet bulk density and mass comparison chart Jupiter Saturn Uranus Neptune",
        "imagePrompt": "Flat vector paired bar chart of Jupiter, Saturn, Uranus and Neptune: one series for mass in Earth masses, another for bulk density in g/cm3, with Neptune highest in density among them.",
        "alt": "A rendered (CGI, not photographic) view of the planet Neptune: a deep-blue globe with the Great Dark Spot and bright white companion cloud streaks, faint thin rings around its equator, lit from…",
        "depictable": true,
        "allowGenerated": true,
        "subject": "A rendered (CGI, not photographic) view of the planet Neptune: a deep-blue globe with the Great Dark Spot and bright white companion cloud streaks, faint thin rings around its equator, lit from the upper right against black space. It is a single planet, not a chart of the four giants.",
        "credit": "Pexels · Zelch Csaba · Pexels License",
        "creditUrl": "https://www.pexels.com/photo/20376398/",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-neptune-smaller-heavier.webp"
      },
      "uid": "2wb3n9xpx17d"
    },
    {
      "id": "ast-f-neptune-one-orbit-since-discovery",
      "shape": "fact",
      "title": "One Orbit Since Discovery",
      "body": "Uranus orbits at about **19 astronomical units**, Neptune at about **30** — the distance that also marks the inner edge of the **Kuiper Belt**. Uranus's year runs **84 Earth years**, so a single season lasts about 21 of ours. Neptune's runs **164.79**: discovered in 1846, it completed its first circuit since discovery only on **12 July 2011**.",
      "source": {
        "label": "NASA Science — Uranus Facts",
        "url": "https://science.nasa.gov/uranus/facts/"
      },
      "tags": [
        "l08p1",
        "ice-giants",
        "orbits"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Neptune full disc Voyager 2 1989 image",
        "entityTerm": "Neptune",
        "imagePrompt": "A full-disc spacecraft photograph of Neptune, deep blue with faint white cirrus streaks, against black space.",
        "alt": "Neptune's deep blue disc as Voyager 2 saw it — a planet that took until 2011 to finish one lap since discovery",
        "depictable": true,
        "credit": "Wikipedia — Neptune · See Wikimedia Commons",
        "creditUrl": "https://en.wikipedia.org/wiki/Neptune",
        "subject": "Wikipedia 'Neptune' article lead image — the genuine color-calibrated Voyager 2 photograph of Neptune's full blue disc with faint dark-spot cloud features; matches the alt text exactly.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-neptune-one-orbit-since-discovery.webp"
      },
      "uid": "1gn400418m8n6w"
    },
    {
      "id": "ast-p-uranus-day-length",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "A day on Uranus"
      },
      "sideB": {
        "modality": "text",
        "value": "About 17 hours — and about 16 for Neptune"
      },
      "source": {
        "label": "JPL Solar System Dynamics — Planetary Physical Parameters",
        "url": "https://ssd.jpl.nasa.gov/planets/phys_par.html"
      },
      "tags": [
        "l08p1",
        "ice-giants",
        "rotation"
      ],
      "uid": "1n2yckl1g7dyqz"
    },
    {
      "id": "ast-d-ice-giant",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Ice giant"
      },
      "definition": {
        "modality": "text",
        "value": "A giant planet whose bulk is a hot fluid of water, methane and ammonia over a rocky core, not the hydrogen and helium of a gas giant"
      },
      "source": {
        "label": "NASA Science — Planets",
        "url": "https://science.nasa.gov/solar-system/planets/"
      },
      "tags": [
        "l08p1",
        "ice-giants",
        "classification"
      ],
      "uid": "vyzx6epj5j3k"
    },
    {
      "id": "ast-q-icegiant-interior",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Neptune is narrower than Uranus yet denser. What does that say about it?"
      },
      "options": [
        {
          "modality": "text",
          "value": "It spins fast enough to compress"
        },
        {
          "modality": "text",
          "value": "It holds more heavy elements"
        },
        {
          "modality": "text",
          "value": "It is much hotter inside"
        },
        {
          "modality": "text",
          "value": "It has a thicker hydrogen skin"
        }
      ],
      "correctIndex": 1,
      "explanation": "Neptune is 1.638 g/cm3 against Uranus's 1.270 — the densest of the four giants. More mass in less volume means a larger share of heavy elements, which is what separates an ice giant from a gas giant. Spin flattens a planet rather than compacting it.",
      "source": {
        "label": "NASA Science — Planets",
        "url": "https://science.nasa.gov/solar-system/planets/"
      },
      "tags": [
        "l08p1",
        "ice-giants",
        "composition"
      ],
      "uid": "nurg3w1javnve"
    },
    {
      "id": "ast-q-neptune-mass-flip",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Neptune is slightly narrower than Uranus yet holds more matter. Which measurement accounts for that?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Escape velocity"
        },
        {
          "modality": "text",
          "value": "Surface gravity"
        },
        {
          "modality": "text",
          "value": "Rotation period"
        },
        {
          "modality": "text",
          "value": "Bulk density"
        }
      ],
      "correctIndex": 3,
      "explanation": "Mass per unit volume is what differs: 1.638 g/cm3 against Uranus's 1.270, so 17.1 Earth masses fit inside 49,528 km. Equatorial diameter is the measurement that makes Neptune the smaller one, not the heavier; sidereal orbital period and axial tilt describe motion, not packing.",
      "source": {
        "label": "JPL Solar System Dynamics — Planetary Physical Parameters",
        "url": "https://ssd.jpl.nasa.gov/planets/phys_par.html"
      },
      "tags": [
        "l08p1",
        "ice-giants",
        "density"
      ],
      "uid": "ka9yg5xyjwxz"
    },
    {
      "id": "ast-f-uranus-rolls-like-barrel",
      "shape": "fact",
      "title": "A Planet On Its Side",
      "body": "Uranus's axis is tilted **97.77 degrees**, against 23.4 for Earth and 28 for Neptune. Past 90 degrees the geometry changes in kind, not in degree: Uranus does not stand upright and lean, it rolls along its orbit like a barrel, poles pointing roughly at and away from the Sun. Each **pole** receives more sunlight across an orbit than the equator does, though measured temperatures do not follow that simply — and any tilt past 90 degrees is **retrograde** by definition, so the backwards spin needs no second explanation.",
      "factVariant": "image-heavy",
      "imageCaption": "Uranus rolls along its orbit rather than standing upright and leaning.",
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "Uranus 98 degree axial tilt rolling along its orbit diagram",
        "imagePrompt": "Flat vector diagram of Uranus at four points around its orbit with its rotation axis lying nearly in the orbital plane, poles alternately facing the Sun, contrasted with Earth's 23.4-degree lean.",
        "alt": "Diagram of Uranus tipped 98 degrees, rolling along its orbit with each pole pointing at the Sun in turn",
        "depictable": true,
        "allowGenerated": true
      },
      "source": {
        "label": "NASA Science — Uranus Facts",
        "url": "https://science.nasa.gov/uranus/facts/"
      },
      "tags": [
        "l08p2",
        "uranus",
        "tilt"
      ],
      "uid": "eptxwp3x8mrp"
    },
    {
      "id": "ast-f-uranus-tilt-hypothesis",
      "shape": "fact",
      "title": "Hypothesis, Not History",
      "body": "NASA's own wording is that the tilt \"may be\" the result of a collision. Smoothed-particle-hydrodynamics simulations find that an impactor of at least about **2 Earth masses** could give the post-impact planet its rapid rotation, while the alternative — a slow **spin-orbit resonance** — struggles to reach 98 degrees even under conditions chosen to favour it. The case rests on simulations reproducing the tilt, not on any trace of an impactor.",
      "source": {
        "label": "Kegerreis et al. (2018), ApJ 861, 52 — giant impacts on early Uranus",
        "url": "https://iopscience.iop.org/article/10.3847/1538-4357/aac725"
      },
      "tags": [
        "l08p2",
        "uranus",
        "giant-impact"
      ],
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "smoothed particle hydrodynamics giant impact simulation of Uranus tilt",
        "imagePrompt": "A sequence of simulation renders showing a roughly two-Earth-mass impactor striking the young Uranus and the resulting debris and spin, frames labelled with elapsed time.",
        "alt": "Simulation frames of a giant impact knocking Uranus onto its side — the evidence is modelled, not observed",
        "depictable": true,
        "allowGenerated": true
      },
      "uid": "wb6dvq159bx5g"
    },
    {
      "id": "ast-f-icegiant-methane-haze",
      "shape": "fact",
      "title": "Why One Blue Is Paler",
      "body": "Both planets look blue-green because **methane** absorbs red light and lets blue and green scatter back out — gas absorption, not water, and there is no ocean to see. Yet Uranus is the paler, milkier cyan, and the two hold almost the same methane. The current explanation is **haze**: the layer thickens in Uranus's sluggish air, while Neptune's more turbulent atmosphere churns methane into it, where it condenses onto the particles and drags them down as **methane snow**.",
      "source": {
        "label": "NASA Science — Uranus Facts",
        "url": "https://science.nasa.gov/uranus/facts/"
      },
      "tags": [
        "l08p2",
        "ice-giants",
        "colour"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Uranus Voyager 2 photograph",
        "imagePrompt": "Documentary-style photograph: Uranus's pale, nearly featureless milky cyan disc, as photographed by Voyager 2 in 1986. Natural light, no readable text, no logos, no watermarks.",
        "alt": "Uranus's pale, nearly featureless milky cyan disc, as photographed by Voyager 2 in 1986",
        "credit": "Wikipedia — Uranus · See Wikimedia Commons",
        "creditUrl": "https://en.wikipedia.org/wiki/Uranus",
        "subject": "The genuine Voyager 2 photograph of Uranus: a full, pale, nearly featureless milky cyan/white disc on black space background — exactly matches the card's alt text.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-icegiant-methane-haze.webp"
      },
      "uid": "g2uez71tsit6z"
    },
    {
      "id": "ast-f-neptune-great-dark-spot",
      "shape": "fact",
      "title": "A Storm That Left",
      "body": "Voyager 2 photographed an Earth-sized storm in Neptune's southern hemisphere in 1989 — the **Great Dark Spot**, about **13,000 by 6,600 km**. When Hubble looked in 1994 it had vanished. Neptune's dark storms last only a few years each, and the later ones have been separate, short-lived storms; Jupiter's Great Red Spot has persisted for well over a century.",
      "source": {
        "label": "NASA Science / Hubble — Hubble Tracks the Lifecycle of Giant Storms on Neptune",
        "url": "https://science.nasa.gov/missions/hubble/hubble-tracks-the-lifecycle-of-giant-storms-on-neptune/"
      },
      "tags": [
        "l08p2",
        "neptune",
        "storms"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Neptune Great Dark Spot Voyager 2 1989 image",
        "entityTerm": "Great Dark Spot",
        "imagePrompt": "A Voyager-style image of Neptune showing the dark elliptical Great Dark Spot with bright companion cirrus clouds along its edge.",
        "alt": "Voyager 2's August 1989 full-disc photograph of Neptune (Wikimedia file Neptune_storms.jpg): the Great Dark Spot is the large dark oval at upper left with bright white companion clouds along its…",
        "depictable": true,
        "credit": "Wikipedia — Small Dark Spot · See Wikimedia Commons",
        "creditUrl": "https://en.wikipedia.org/wiki/Small_Dark_Spot",
        "subject": "Voyager 2's August 1989 full-disc photograph of Neptune (Wikimedia file Neptune_storms.jpg): the Great Dark Spot is the large dark oval at upper left with bright white companion clouds along its edge, the small white cloud \"Scooter\" sits below it, and the Small Dark Spot with its bright core is at l",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-neptune-great-dark-spot.webp"
      },
      "uid": "jowyd1thkplp"
    },
    {
      "id": "ast-p-uranus-literary-moons",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Moons with literary names"
      },
      "sideB": {
        "modality": "text",
        "value": "Uranus's — Miranda, Ariel, Umbriel, Titania and Oberon",
        "short": "Uranus's, from Shakespeare and Pope"
      },
      "source": {
        "label": "NASA Science — Uranus Facts",
        "url": "https://science.nasa.gov/uranus/facts/"
      },
      "tags": [
        "l08p2",
        "uranus",
        "moons"
      ],
      "uid": "d8wcz37pfnvr"
    },
    {
      "id": "ast-d-coronae-miranda",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Coronae"
      },
      "definition": {
        "modality": "text",
        "value": "Lightly cratered patchworks of ridges and valleys on Uranus's moon Miranda, a landform of a kind seen on no other moon"
      },
      "source": {
        "label": "NASA Science — Miranda",
        "url": "https://science.nasa.gov/uranus/moons/miranda/"
      },
      "tags": [
        "l08p2",
        "uranus",
        "miranda"
      ],
      "uid": "xi81cg14rub2"
    },
    {
      "id": "ast-q-uranus-hottest-region",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Across a full Uranian orbit, which part receives the most sunlight?"
      },
      "options": [
        {
          "modality": "text",
          "value": "The equator"
        },
        {
          "modality": "text",
          "value": "The poles"
        },
        {
          "modality": "text",
          "value": "The tropics"
        },
        {
          "modality": "text",
          "value": "The mid-latitudes"
        }
      ],
      "correctIndex": 1,
      "explanation": "Tipped 97.77 degrees, Uranus rolls along its orbit with each pole pointing roughly at and away from the Sun. The equator, the tropics and the mid-latitudes all take the Sun low and glancing — the reverse of Earth, whose 23.4-degree tilt keeps the equator most directly lit.",
      "source": {
        "label": "NASA Science — Uranus Facts",
        "url": "https://science.nasa.gov/uranus/facts/"
      },
      "tags": [
        "l08p2",
        "uranus",
        "tilt"
      ],
      "uid": "19o3u6rdjs6xx"
    },
    {
      "id": "ast-q-fastest-winds-planet",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Which planet has the fastest winds in the Solar System?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Neptune"
        },
        {
          "modality": "text",
          "value": "Jupiter"
        },
        {
          "modality": "text",
          "value": "Uranus"
        },
        {
          "modality": "text",
          "value": "Saturn"
        }
      ],
      "correctIndex": 0,
      "explanation": "NASA puts Neptune's peak winds near 2,000 km/h. Saturn's reach about 1,800, Uranus's about 900 and Jupiter's about 600 — the largest planet is nowhere near the windiest. Neptune gets the least sunlight yet radiates over twice the energy it absorbs, and that heat drives the winds.",
      "source": {
        "label": "NASA Science — Neptune Facts",
        "url": "https://science.nasa.gov/neptune/facts/"
      },
      "tags": [
        "l08p2",
        "neptune",
        "winds"
      ],
      "uid": "1wx09jl18r1kfj"
    },
    {
      "id": "czr-ast-d-coronae-miranda",
      "shape": "cloze",
      "derivedFrom": "ast-d-coronae-miranda",
      "template": "___ — Lightly cratered patchworks of ridges and valleys on Uranus's moon Miranda, a landform of a kind seen on no other moon",
      "answer": "Coronae",
      "distractors": [
        "Penumbra",
        "Coronal hole",
        "Exosphere"
      ],
      "explanation": "Coronae is lightly cratered patchworks of ridges and valleys on Uranus's moon Miranda, a landform of a kind seen on no other moon. Penumbra, the closest of the alternatives, is the outer part of a shadow, where the light source is partly blocked rather than hidden completely.",
      "source": {
        "label": "NASA Science — Miranda",
        "url": "https://science.nasa.gov/uranus/moons/miranda/"
      },
      "tags": [
        "l08p2",
        "uranus",
        "miranda",
        "derived"
      ],
      "uid": "14abb5jrqd5x3"
    },
    {
      "id": "tfr-ast-d-coronae-miranda",
      "shape": "trueFalse",
      "derivedFrom": "ast-d-coronae-miranda",
      "statement": "Coronae — lightly cratered patchworks of ridges and valleys on Uranus's moon Miranda, a landform of a kind seen on no other moon.",
      "isTrue": true,
      "why": "Coronae are the lightly cratered patchworks of ridges and valleys on Uranus's moon Miranda, a landform of a kind seen on no other moon. The exosphere is a layer of gas rather than a landform: the outermost gas of a world, so thin its atoms almost never collide.",
      "source": {
        "label": "NASA Science — Miranda",
        "url": "https://science.nasa.gov/uranus/moons/miranda/"
      },
      "tags": [
        "l08p2",
        "uranus",
        "miranda",
        "derived"
      ],
      "uid": "1zlgauvgbl48"
    },
    {
      "id": "ast-f-neptune-found-on-paper",
      "shape": "fact",
      "title": "Found On Paper First",
      "body": "Uranus was found by accident: **William Herschel** spotted it on **13 March 1781** and first took it for a comet. Neptune was found the other way round. Uranus's orbit misbehaved, so **Urbain Le Verrier** in France and, independently, **John Couch Adams** in England calculated where an unseen planet must be. **Johann Galle** in Berlin turned a telescope on Le Verrier's figure on **23 September 1846** and found it that first night, within about a degree of the prediction.",
      "source": {
        "label": "NASA Science — Neptune Facts",
        "url": "https://science.nasa.gov/neptune/facts/"
      },
      "tags": [
        "l08p3",
        "neptune",
        "discovery"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Urbain Le Verrier portrait",
        "entityTerm": "Urbain Le Verrier",
        "subjectType": "person",
        "profile": "archive-first",
        "imagePrompt": "A historical portrait photograph or engraving of the nineteenth-century French astronomer Urbain Le Verrier.",
        "alt": "Urbain Le Verrier, who calculated where Neptune had to be before anyone looked for it",
        "depictable": true,
        "credit": "User Magnus Manske on en.wikipedia · Public domain",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:Urbain_Le_Verrier.jpg",
        "subject": "Identical file to index 1/4: the canonical public-domain lithograph portrait bust of Urbain Le Verrier, sourced directly from its own Wikimedia Commons file page titled 'File:Urbain Le Verrier.jpg'",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-neptune-found-on-paper.webp"
      },
      "uid": "rex2zerggb6w"
    },
    {
      "id": "ast-f-uranus-rings-occultation",
      "shape": "fact",
      "title": "Rings Found By Blinking Starlight",
      "body": "On **10 March 1977** astronomers watched Uranus pass in front of the star SAO 158687. The starlight blinked out several times before and after the planet itself covered it — Uranus has rings. They are extremely dark and very narrow, and the count is unsettled: NASA describes nine inner rings plus two outer ones, while Wikipedia lists thirteen. The telescope was airborne, and nine years early for Voyager 2.",
      "source": {
        "label": "NASA Science — Uranus: Exploration timeline",
        "url": "https://science.nasa.gov/uranus/exploration/"
      },
      "tags": [
        "l08p3",
        "uranus",
        "rings"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Uranus rings Voyager 2 1986",
        "imagePrompt": "Documentary-style photograph: A grainy Voyager 2 photograph of Uranus's rings, seen nearly edge-on as thin, dark arcs. Natural light, no readable text, no logos, no watermarks.",
        "alt": "A grainy Voyager 2 photograph of Uranus's rings, seen nearly edge-on as thin, dark arcs",
        "credit": "NASA · Public domain",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:Uranus_rings_and_two_moons.jpg",
        "subject": "A genuine grainy black-and-white Voyager 2 photograph: Uranus's bright overexposed limb with faint thin ring arcs visible lower-right, and two small moons circled and labeled '1986U7'/'1986U8'.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-uranus-rings-occultation.webp"
      },
      "uid": "1pv813bypx2gt"
    },
    {
      "id": "ast-f-triton-cold-is-not-dead",
      "shape": "fact",
      "title": "Cold Is Not Dead",
      "body": "**Triton**, about **2,700 km** across, holds more than 99.5 percent of all the mass known to orbit Neptune. **William Lassell** found it on 10 October 1846, 17 days after the planet. It is the only large moon circling its planet against that planet's own spin — NASA writes that scientists think it was captured from the Kuiper Belt. Voyager 2 saw **geysers** venting nitrogen gas and dark dust at about **minus 235 °C**.",
      "factVariant": "image-heavy",
      "imageCaption": "Triton vents nitrogen geysers at a surface temperature of about minus 235 degrees Celsius.",
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Triton moon of Neptune Voyager 2 cantaloupe terrain nitrogen geysers",
        "entityTerm": "Triton (moon)",
        "imagePrompt": "A Voyager-style image of Neptune's moon Triton showing the pinkish south polar cap, dimpled cantaloupe terrain, and dark wind-blown geyser streaks.",
        "alt": "Triton's cantaloupe terrain and the dark streaks its nitrogen geysers have laid down across the polar cap",
        "depictable": true,
        "credit": "NASA / Jet Propulsion Lab / U.S. Geological Survey · Public domain",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:Triton_moon_mosaic_Voyager_2_(large).jpg",
        "subject": "The canonical color Voyager 2 mosaic of Triton (public domain, NASA/JPL/USGS): cantaloupe terrain filling the upper-left of the disc and a pale pinkish-white south polar ice cap in the lower half marked with dark diagonal wind/geyser-deposit streaks — matches the alt text's two named features direct",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-triton-cold-is-not-dead.webp"
      },
      "source": {
        "label": "NASA Science — Triton",
        "url": "https://science.nasa.gov/neptune/neptune-moons/triton/"
      },
      "tags": [
        "l08p3",
        "neptune",
        "triton"
      ],
      "uid": "1q86brjv7p5cr"
    },
    {
      "id": "ast-p-neptune-ring-names",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Neptune's five main rings"
      },
      "sideB": {
        "modality": "text",
        "value": "Galle, Le Verrier, Lassell, Arago and Adams"
      },
      "source": {
        "label": "NASA Science — Neptune Facts",
        "url": "https://science.nasa.gov/neptune/facts/"
      },
      "tags": [
        "l08p3",
        "neptune",
        "rings"
      ],
      "uid": "1smvh21yocwtn"
    },
    {
      "id": "ast-p-neptune-moon-names",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Neptune's moons are named for"
      },
      "sideB": {
        "modality": "text",
        "value": "Lesser sea gods and nymphs of Greek myth"
      },
      "source": {
        "label": "NASA Science — Neptune Moons",
        "url": "https://science.nasa.gov/neptune/neptune-moons/"
      },
      "tags": [
        "l08p3",
        "neptune",
        "moons"
      ],
      "uid": "19l1vdq1oo6a64"
    },
    {
      "id": "ast-d-occultation",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Occultation"
      },
      "definition": {
        "modality": "text",
        "value": "One body passing in front of a star, where the pattern of the starlight's dimming maps structures far too faint to photograph"
      },
      "source": {
        "label": "NASA Science — Uranus: Exploration timeline",
        "url": "https://science.nasa.gov/uranus/exploration/"
      },
      "tags": [
        "l08p3",
        "uranus",
        "method"
      ],
      "uid": "1q8mcza1tbpery"
    },
    {
      "id": "ast-q-neptune-discovery-method",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "How was Neptune first located?"
      },
      "options": [
        {
          "modality": "text",
          "value": "By an accidental sighting"
        },
        {
          "modality": "text",
          "value": "By calculating where it must be"
        },
        {
          "modality": "text",
          "value": "By watching it move nightly"
        },
        {
          "modality": "text",
          "value": "By a systematic sky survey"
        }
      ],
      "correctIndex": 1,
      "explanation": "Le Verrier's figures told Galle where to point, and the planet stood within about a degree of the prediction on his first night. Watching something move confirms a planet but will not find one at 30 AU; no survey was involved; and nothing about it was accidental.",
      "source": {
        "label": "NASA Science — Neptune Facts",
        "url": "https://science.nasa.gov/neptune/facts/"
      },
      "tags": [
        "l08p3",
        "neptune",
        "discovery"
      ],
      "uid": "5x4627dymwm1"
    },
    {
      "id": "ast-q-icegiant-only-visitor",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Which spacecraft has flown past both ice giants?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Galileo"
        },
        {
          "modality": "text",
          "value": "Juno"
        },
        {
          "modality": "text",
          "value": "Cassini"
        },
        {
          "modality": "text",
          "value": "Voyager 2"
        }
      ],
      "correctIndex": 3,
      "explanation": "It passed Uranus on 24 January 1986 at about 81,500 km from the cloud tops and Neptune on 25 August 1989 at about 4,800 km — the only close visits either planet has had. Cassini orbited Saturn; Galileo and Juno went to Jupiter. Neither ice giant has ever had an orbiter.",
      "source": {
        "label": "NASA Science — Voyager 2",
        "url": "https://science.nasa.gov/mission/voyager/voyager-2/"
      },
      "tags": [
        "l08p3",
        "ice-giants",
        "exploration"
      ],
      "uid": "1sxooy51182t1b"
    },
    {
      "id": "czr-ast-d-occultation",
      "shape": "cloze",
      "derivedFrom": "ast-d-occultation",
      "template": "___ — One body passing in front of a star, where the pattern of the starlight's dimming maps structures far too faint to photograph",
      "answer": "Occultation",
      "distractors": [
        "Synodic month",
        "Equinox",
        "Solar flare"
      ],
      "explanation": "Occultation is one body passing in front of a star, where the pattern of the starlight's dimming maps structures far too faint to photograph — not Synodic month.",
      "source": {
        "label": "NASA Science — Uranus: Exploration timeline",
        "url": "https://science.nasa.gov/uranus/exploration/"
      },
      "tags": [
        "l08p3",
        "uranus",
        "method",
        "derived"
      ],
      "uid": "1eiz9uxodckg7"
    },
    {
      "id": "tfr-ast-d-occultation",
      "shape": "trueFalse",
      "derivedFrom": "ast-d-occultation",
      "statement": "Occultation — a Martian solar day of 24 hours 39 minutes 35 seconds.",
      "isTrue": false,
      "why": "An occultation is one body passing in front of a star, where the pattern of the starlight's dimming maps structures far too faint to photograph. A sol is a unit of time on Mars: one Martian solar day of 24 hours 39 minutes 35 seconds.",
      "source": {
        "label": "NASA Science — Uranus: Exploration timeline",
        "url": "https://science.nasa.gov/uranus/exploration/"
      },
      "tags": [
        "l08p3",
        "uranus",
        "method",
        "derived"
      ],
      "whyOptions": [
        "Equinox",
        "Sol",
        "Synodic month"
      ],
      "whyCorrectIndex": 1,
      "uid": "1xdnhfm15kaz3o"
    },
    {
      "id": "ast-f-belt-unfinished-planet",
      "shape": "fact",
      "title": "An Unfinished Planet",
      "body": "No planet formed between Mars and Jupiter because **Jupiter's gravity** kept the local planetesimals agitated — instead of merging they collided and fragmented, and those fragments are the asteroids. The belt is an unfinished planet, not a broken one, and the arithmetic agrees: everything in it put together weighs **less than Earth's Moon**, with **Ceres** alone holding about **25 percent** of that total.",
      "source": {
        "label": "ESA — Asteroids",
        "url": "https://www.esa.int/Science_Exploration/Space_Science/Asteroids"
      },
      "tags": [
        "l09p1",
        "asteroid-belt",
        "formation"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Ceres dwarf planet Dawn spacecraft global view Occator crater",
        "entityTerm": "Ceres (dwarf planet)",
        "imagePrompt": "A full-globe spacecraft image of Ceres, grey and cratered, with the bright carbonate deposits of Occator crater visible.",
        "alt": "Ceres, which alone holds about a quarter of everything in the asteroid belt — and the belt totals less than the Moon",
        "depictable": true,
        "credit": "Wikipedia — Geology of Ceres · See Wikimedia Commons",
        "creditUrl": "https://en.wikipedia.org/wiki/Geology_of_Ceres",
        "subject": "A crisp, fully-lit grayscale global portrait of Ceres from Dawn: a heavily cratered sphere with the bright Occator-crater spots clearly visible near the disc's center (the well-known 'Ceres global hi-res' NASA/JPL image, used on the Geology of Ceres article).",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-belt-unfinished-planet.webp"
      },
      "uid": "10diuws15xgt7s"
    },
    {
      "id": "ast-f-belt-mostly-empty",
      "shape": "fact",
      "title": "Emptier Than It Looks",
      "body": "The main belt holds an estimated **1.1 to 1.9 million** asteroids larger than 1 km and is still overwhelmingly empty space. Spacecraft cross it with **virtually no chance of a collision**: **Pioneer 10** entered the belt on 15 July 1972 and emerged in February 1973. The film version has it backwards — reaching even one asteroid takes deliberate aim.",
      "factVariant": "image-heavy",
      "imageCaption": "A million rocks spread through that volume still leaves millions of kilometres between neighbours.",
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "asteroid belt true spacing between asteroids scale diagram",
        "imagePrompt": "Flat vector diagram contrasting the popular dense-rubble depiction with a to-scale panel in which neighbouring asteroids are hundreds of thousands of kilometres apart, a spacecraft track threading through untouched.",
        "alt": "Diagram of the asteroid belt drawn at true spacing — millions of bodies, and still overwhelmingly empty",
        "depictable": true,
        "allowGenerated": true
      },
      "source": {
        "label": "NASA Science — Asteroid Facts",
        "url": "https://science.nasa.gov/solar-system/asteroids/facts/"
      },
      "tags": [
        "l09p1",
        "asteroid-belt",
        "density"
      ],
      "uid": "zqtmzf1rn2921"
    },
    {
      "id": "ast-f-vesta-differentiated",
      "shape": "fact",
      "title": "The Asteroid That Melted",
      "body": "**Vesta**, about **523 km** across, is the largest asteroid and the odd one out. Most asteroids are unprocessed rubble; Vesta is **differentiated** — it melted early and separated into crust, mantle and core, like a small planet. NASA's **Dawn** orbited it from 16 July 2011 to 5 September 2012 before flying on to Ceres — the one body in the belt more massive still, and the reason Vesta holds the title of largest asteroid at all: at 939 km Ceres was reclassified as a dwarf planet in 2006 and stopped counting as one.",
      "source": {
        "label": "JPL Small-Body Database — 4 Vesta (physical parameters)",
        "url": "https://ssd-api.jpl.nasa.gov/sbdb.api?sstr=4%20Vesta&phys-par=true"
      },
      "tags": [
        "l09p1",
        "vesta",
        "differentiation"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Vesta asteroid Dawn spacecraft global view Rheasilvia basin",
        "entityTerm": "4 Vesta",
        "imagePrompt": "A full-globe spacecraft image of the asteroid Vesta showing its irregular shape, heavy cratering and the huge Rheasilvia impact basin at the south pole.",
        "alt": "Vesta from orbit: the largest asteroid, and one that melted and separated into crust, mantle and core",
        "depictable": true,
        "credit": "Wikipedia — 4 Vesta · See Wikimedia Commons",
        "creditUrl": "https://en.wikipedia.org/wiki/4_Vesta",
        "subject": "The actual NASA Dawn spacecraft mosaic of asteroid 4 Vesta: a heavily cratered, oblong gray-tan body filling the frame against black space, matching the card's subject exactly.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-vesta-differentiated.webp"
      },
      "uid": "1b01ch51o1ztp7"
    },
    {
      "id": "ast-f-jupiter-trojan-swarms",
      "shape": "fact",
      "title": "Parking Spaces at Sixty Degrees",
      "body": "Jupiter's **Trojan asteroids** do not orbit Jupiter. They share its orbit around the Sun in two swarms that lead and trail the planet by **60 degrees**, at the **L4 and L5** Lagrange points — each swarm sitting at the third corner of an equilateral triangle with Jupiter and the Sun. Together the swarms may rival the main belt in number; the largest Trojan is about 250 km wide. NASA's **Lucy**, launched 16 October 2021, is the first mission to visit them.",
      "source": {
        "label": "NASA Science — Asteroid Facts",
        "url": "https://science.nasa.gov/solar-system/asteroids/facts/"
      },
      "tags": [
        "l09p1",
        "trojans",
        "lagrange-points"
      ],
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "Jupiter Trojan asteroids L4 L5 Lagrange swarms orbit diagram",
        "imagePrompt": "Flat vector orbital diagram: the Sun at centre, Jupiter's orbit drawn as a circle, and two clouds of dots at the L4 and L5 points sixty degrees ahead and behind, each forming an equilateral triangle with Jupiter and the Sun.",
        "alt": "Diagram of the two Trojan swarms sitting sixty degrees ahead of and behind Jupiter on its own orbit",
        "depictable": true,
        "allowGenerated": true
      },
      "uid": "ioyc7d19pt2w9"
    },
    {
      "id": "ast-p-asteroid-belt-distance",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Main asteroid belt"
      },
      "sideB": {
        "modality": "text",
        "value": "Densest between about 2.12 and 3.3 AU from the Sun",
        "short": "About 2.12 to 3.3 AU"
      },
      "source": {
        "label": "Swinburne University COSMOS — Main Asteroid Belt",
        "url": "https://astronomy.swin.edu.au/cosmos/*/Main+Asteroid+Belt"
      },
      "tags": [
        "l09p1",
        "asteroid-belt",
        "distance"
      ],
      "uid": "1oyty6f1d1bqz1"
    },
    {
      "id": "ast-p-pallas-inclination",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Pallas"
      },
      "sideB": {
        "modality": "text",
        "value": "Tilted 34.9 degrees out of the planets' plane"
      },
      "source": {
        "label": "JPL Small-Body Database — 2 Pallas (physical and orbital parameters)",
        "url": "https://ssd-api.jpl.nasa.gov/sbdb.api?sstr=2%20Pallas&phys-par=true"
      },
      "tags": [
        "l09p1",
        "pallas",
        "orbit"
      ],
      "uid": "146zeowuhvdvm"
    },
    {
      "id": "ast-d-differentiated",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Differentiated"
      },
      "definition": {
        "modality": "text",
        "value": "Melted early enough that dense metal sank and light rock floated, leaving a body sorted into crust, mantle and core"
      },
      "curatedDistractors": [
        "Carbonaceous",
        "Metallic",
        "Fragmented"
      ],
      "source": {
        "label": "JPL Small-Body Database — 4 Vesta (physical parameters)",
        "url": "https://ssd-api.jpl.nasa.gov/sbdb.api?sstr=4%20Vesta&phys-par=true"
      },
      "tags": [
        "l09p1",
        "vesta",
        "vocabulary"
      ],
      "uid": "e11fxt18lhfp"
    },
    {
      "id": "ast-q-belt-no-planet",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Why is there no planet in the main asteroid belt?"
      },
      "options": [
        {
          "modality": "text",
          "value": "A passing star pulled it away"
        },
        {
          "modality": "text",
          "value": "Jupiter's gravity stirred it up"
        },
        {
          "modality": "text",
          "value": "The Sun boiled the material away"
        },
        {
          "modality": "text",
          "value": "A planet there was blown apart"
        }
      ],
      "correctIndex": 1,
      "explanation": "Everything in the belt together weighs less than Earth's Moon, so no planet was ever blown apart to supply it — and neither the Sun nor a passing star is involved. Jupiter's pull kept the planetesimals colliding and fragmenting instead of merging.",
      "source": {
        "label": "ESA — Asteroids",
        "url": "https://www.esa.int/Science_Exploration/Space_Science/Asteroids"
      },
      "tags": [
        "l09p1",
        "asteroid-belt",
        "quiz"
      ],
      "uid": "1gesda718ik4sx"
    },
    {
      "id": "ast-q-asteroid-c-type-share",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "What share of visible asteroids are the dark carbonaceous kind?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Over 75 percent"
        },
        {
          "modality": "text",
          "value": "Under 5 percent"
        },
        {
          "modality": "text",
          "value": "About 40 percent"
        },
        {
          "modality": "text",
          "value": "About 17 percent"
        }
      ],
      "correctIndex": 0,
      "explanation": "C-types are the commonest class by a wide margin. About 17 percent is the S-type share, while 40 percent or under 5 percent would leave the stony and metallic classes badly misweighted. The letters come from reflectance surveys, so treat the figures as estimates.",
      "source": {
        "label": "Wikipedia — Asteroid belt / C-type asteroid (retrieved 2026-08-09)",
        "url": "https://en.wikipedia.org/wiki/C-type_asteroid"
      },
      "tags": [
        "l09p1",
        "asteroid-types",
        "quiz"
      ],
      "uid": "4ava1y1q03se"
    },
    {
      "id": "czr-ast-d-differentiated",
      "shape": "cloze",
      "derivedFrom": "ast-d-differentiated",
      "template": "___ — Melted early enough that dense metal sank and light rock floated, leaving a body sorted into crust, mantle and core",
      "answer": "Differentiated",
      "distractors": [
        "Retrograde",
        "Runaway greenhouse",
        "Tidal heating"
      ],
      "explanation": "Differentiated is melted early enough that dense metal sank and light rock floated, leaving a body sorted into crust, mantle and core. Retrograde, the closest of the alternatives, is motion running opposite to the usual direction in a system.",
      "source": {
        "label": "JPL Small-Body Database — 4 Vesta (physical parameters)",
        "url": "https://ssd-api.jpl.nasa.gov/sbdb.api?sstr=4%20Vesta&phys-par=true"
      },
      "tags": [
        "l09p1",
        "vesta",
        "vocabulary",
        "derived"
      ],
      "uid": "12qo2b2vjt30g"
    },
    {
      "id": "tfr-ast-d-differentiated",
      "shape": "trueFalse",
      "derivedFrom": "ast-d-differentiated",
      "statement": "Differentiated — melted early enough that dense metal sank and light rock floated, leaving a body sorted into crust, mantle and core.",
      "isTrue": true,
      "why": "A differentiated body melted early enough that dense metal sank and light rock floated, leaving it sorted into crust, mantle and core — the reason Earth has an iron centre at all. Retrograde describes direction rather than structure: motion running opposite to the usual sense in a system.",
      "source": {
        "label": "JPL Small-Body Database — 4 Vesta (physical parameters)",
        "url": "https://ssd-api.jpl.nasa.gov/sbdb.api?sstr=4%20Vesta&phys-par=true"
      },
      "tags": [
        "l09p1",
        "vesta",
        "vocabulary",
        "derived"
      ],
      "uid": "ybprxjl1lc2v"
    },
    {
      "id": "ast-f-meteor-three-words",
      "shape": "fact",
      "title": "Three Words, Three Places",
      "body": "A **meteoroid** is the rock while it is still in space — anything from a dust grain to a small asteroid. A **meteor** is the streak of light made when that rock enters the atmosphere at speed and burns up. A **meteorite** is what is left if a fragment survives the fall and reaches the ground. The middle word is the one that trips people: a meteor is not an object at all, it is the glow of heated air and vaporised rock.",
      "factVariant": "image-heavy",
      "imageCaption": "Location decides the word: in space, in the air, on the ground.",
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "meteoroid meteor meteorite three stages diagram space atmosphere ground",
        "imagePrompt": "Flat vector three-panel diagram: a rock drifting in space labelled meteoroid, the same rock glowing as a streak in the atmosphere labelled meteor, and the surviving fragment on the ground labelled meteorite.",
        "alt": "Diagram of one rock in three places: meteoroid in space, meteor as the glow in the air, meteorite on the ground",
        "depictable": true,
        "allowGenerated": true
      },
      "source": {
        "label": "NASA Science — Meteors and Meteorites",
        "url": "https://science.nasa.gov/solar-system/meteors-meteorites/"
      },
      "tags": [
        "l09p2",
        "meteors",
        "vocabulary"
      ],
      "uid": "fhissbjjprb7"
    },
    {
      "id": "ast-f-meteoritic-dust-daily",
      "shape": "fact",
      "title": "Forty-Four Tonnes a Day",
      "body": "NASA estimates that about **44 tonnes** of meteoritic material falls on Earth every day, and almost all of it is dust too small to notice. Treat that as an estimate rather than a measurement: Royal Museums Greenwich quotes about **14 tonnes a day** for space dust specifically, and published figures span roughly **5 to 50 tonnes** depending on which particle sizes get counted.",
      "source": {
        "label": "NASA Science — Meteors and Meteorites",
        "url": "https://science.nasa.gov/solar-system/meteors-meteorites/"
      },
      "tags": [
        "l09p2",
        "meteors",
        "accretion"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "micrometeorite cosmic dust particle scanning electron microscope image",
        "entityTerm": "Micrometeorite",
        "imagePrompt": "A scanning electron microscope image of a single roughly spherical micrometeorite showing its melted, pitted surface texture, with a micron scale bar.",
        "alt": "AI-generated rendering styled as a scanning electron micrograph: a single rough, pitted grey spherule filling the frame, with a \"50 µm\" scale bar in the corner implying a grain roughly 150 µm across.",
        "depictable": true,
        "credit": "AI-generated (gpt-image-1.5)",
        "subject": "AI-generated rendering styled as a scanning electron micrograph: a single rough, pitted grey spherule filling the frame, with a \"50 µm\" scale bar in the corner implying a grain roughly 150 µm across. Not a real micrograph; no specific particle is shown.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-meteoritic-dust-daily.webp"
      },
      "uid": "1o67ztfjaz91j"
    },
    {
      "id": "ast-f-meteor-shower-radiant",
      "shape": "fact",
      "title": "Named for a Perspective",
      "body": "An annual **meteor shower** is Earth crossing a stream of dusty debris shed along the orbit of a comet — or, more rarely, an asteroid, which is why the same showers return on the same dates. The **Perseids** peak on 12–13 August, and every Perseid is a fragment of comet **109P/Swift-Tuttle**, whose nucleus is about 26 km across. A shower is named for its **radiant**, the constellation the meteors appear to stream from — a perspective effect, not an origin.",
      "source": {
        "label": "NASA Science — Perseids",
        "url": "https://science.nasa.gov/solar-system/meteors-meteorites/perseids/"
      },
      "tags": [
        "l09p2",
        "meteor-showers",
        "perseids"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Perseid meteor shower long exposure meteors radiating from one point",
        "entityTerm": "Perseids",
        "imagePrompt": "A composite long-exposure night sky photograph of many meteors whose streaks all trace back to a single radiant point among the stars.",
        "alt": "A composite of shower meteors whose trails, extended backwards, all converge on a single point in one constellation",
        "depictable": true,
        "credit": "Unsplash · Shreshth Gupta · Unsplash License",
        "creditUrl": "https://unsplash.com/photos/white-fireworks-over-green-trees-and-mountain-during-daytime-5yiwbYsH91E",
        "subject": "A long-exposure composite over a dark ridge/mountain silhouette showing dozens of bright meteor trails radiating outward from a single point near the top of frame — a genuine radiant composite matching the alt text exactly",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-meteor-shower-radiant.webp"
      },
      "uid": "eh053vgesjjf"
    },
    {
      "id": "ast-f-meteorite-falls-finds",
      "shape": "fact",
      "title": "Stony Falls, Iron Finds",
      "body": "What lands comes in three kinds: **stony** meteorites are mainly silicate rock, **iron** mainly iron-nickel metal, **stony-iron** roughly equal parts of both. More than **95 percent** of meteorites seen to **fall** are stony. Irons are over-represented in collections because they weather slowly and look nothing like Earth rock, so they keep being picked up as **finds** long after landing.",
      "source": {
        "label": "NASA ARES — What are Meteorites?",
        "url": "https://ares.jsc.nasa.gov/meteorite-falls/what-are-meteorites/"
      },
      "tags": [
        "l09p2",
        "meteorites",
        "classification"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "iron meteorite polished etched slice Widmanstatten pattern",
        "entityTerm": "Widmanstätten pattern",
        "imagePrompt": "A photograph of a polished and acid-etched slice of an iron meteorite showing the crosshatched interlocking metallic Widmanstatten bands.",
        "alt": "A cut and etched iron meteorite showing the interlocking Widmanstatten pattern that gives irons away as obviously not from Earth",
        "depictable": true,
        "credit": "H. Raab (User:Vesta) · CC BY-SA 3.0",
        "creditUrl": "https://en.wikipedia.org/wiki/Widmanst%C3%A4tten_pattern",
        "subject": "Polished and acid-etched slice of the Toluca iron meteorite on white background, showing a clean, complete crosshatched Widmanstätten pattern — exactly what the alt text describes; this is the lead image of Wikipedia's own 'Widmanstätten pattern' article",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-meteorite-falls-finds.webp"
      },
      "uid": "1piy4fi1gli55i"
    },
    {
      "id": "ast-p-leonids-tempel-tuttle",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Leonids"
      },
      "sideB": {
        "modality": "text",
        "value": "Comet 55P/Tempel-Tuttle's dust, which can storm roughly every 33 years",
        "short": "Comet 55P/Tempel-Tuttle's dust"
      },
      "source": {
        "label": "NASA Science — Leonids",
        "url": "https://science.nasa.gov/solar-system/meteors-meteorites/leonids/"
      },
      "tags": [
        "l09p2",
        "meteor-showers",
        "leonids"
      ],
      "uid": "1qujujwu97g02"
    },
    {
      "id": "ast-p-chondrite-never-melted",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Chondrites"
      },
      "sideB": {
        "modality": "text",
        "value": "The stony meteorites that never melted or sorted into layers",
        "short": "Never melted, never layered"
      },
      "source": {
        "label": "NASA ARES — What are Meteorites?",
        "url": "https://ares.jsc.nasa.gov/meteorite-falls/what-are-meteorites/"
      },
      "tags": [
        "l09p2",
        "meteorites",
        "chondrites"
      ],
      "uid": "v1tmiuknv8pu"
    },
    {
      "id": "ast-d-rock-comet",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Rock comet"
      },
      "definition": {
        "modality": "text",
        "value": "An asteroid that feeds a meteor shower by cracking and shedding dust in the Sun's heat, growing no tail of boiled-off ice"
      },
      "curatedDistractors": [
        "Radiant",
        "Chondrite",
        "Fireball"
      ],
      "source": {
        "label": "NASA Science — Geminids",
        "url": "https://science.nasa.gov/solar-system/meteors-meteorites/geminids/"
      },
      "tags": [
        "l09p2",
        "geminids",
        "vocabulary"
      ],
      "uid": "bdy1jh10di53p"
    },
    {
      "id": "ast-q-meteor-is-light",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Which of these words names light rather than an object?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Meteoroid"
        },
        {
          "modality": "text",
          "value": "Chondrite"
        },
        {
          "modality": "text",
          "value": "Meteor"
        },
        {
          "modality": "text",
          "value": "Meteorite"
        }
      ],
      "correctIndex": 2,
      "explanation": "A meteor is the glow of heated air and vaporised rock, not something you could hold. A meteoroid is the rock while it is still in space, a meteorite is what reaches the ground, and a chondrite is a stony meteorite that never melted.",
      "source": {
        "label": "NASA Science — Meteors and Meteorites",
        "url": "https://science.nasa.gov/solar-system/meteors-meteorites/"
      },
      "tags": [
        "l09p2",
        "meteors",
        "quiz"
      ],
      "uid": "do6q4qoajb6c"
    },
    {
      "id": "ast-q-geminids-parent-body",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "What sheds the debris behind the December Geminids?"
      },
      "options": [
        {
          "modality": "text",
          "value": "A near-Earth asteroid"
        },
        {
          "modality": "text",
          "value": "A short-period comet"
        },
        {
          "modality": "text",
          "value": "A long-period comet"
        },
        {
          "modality": "text",
          "value": "A stream of interstellar dust"
        }
      ],
      "correctIndex": 0,
      "explanation": "Their parent is 3200 Phaethon, about 5 to 6 km across, which grows no tail and whose spectrum looks rocky — hence 'rock comet'. Comets supply the Perseids and the Leonids, but not this shower, and its debris comes from neither the Moon nor beyond the Solar System.",
      "source": {
        "label": "NASA Science — Geminids",
        "url": "https://science.nasa.gov/solar-system/meteors-meteorites/geminids/"
      },
      "tags": [
        "l09p2",
        "geminids",
        "quiz"
      ],
      "uid": "1p89mi0v9efc2"
    },
    {
      "id": "czr-ast-d-rock-comet",
      "shape": "cloze",
      "derivedFrom": "ast-d-rock-comet",
      "template": "___ — An asteroid that feeds a meteor shower by cracking and shedding dust in the Sun's heat, growing no tail of boiled-off ice",
      "answer": "Rock comet",
      "distractors": [
        "Fireball",
        "Ice giant",
        "Dwarf planet"
      ],
      "explanation": "Rock comet is an asteroid that feeds a meteor shower by cracking and shedding dust in the Sun's heat, growing no tail of boiled-off ice. Fireball, the closest of the alternatives, is a meteor brighter than magnitude −4, about as bright as Venus at its best.",
      "source": {
        "label": "NASA Science — Geminids",
        "url": "https://science.nasa.gov/solar-system/meteors-meteorites/geminids/"
      },
      "tags": [
        "l09p2",
        "geminids",
        "vocabulary",
        "derived"
      ],
      "uid": "1mbnjjks8gmdi"
    },
    {
      "id": "tfr-ast-d-rock-comet",
      "shape": "trueFalse",
      "derivedFrom": "ast-d-rock-comet",
      "statement": "Rock comet — a meteor brighter than magnitude −4, about as bright as Venus at its best.",
      "isTrue": false,
      "why": "A fireball is a meteor brighter than magnitude −4, about as bright as Venus at its best. A rock comet is an asteroid rather than a meteor: one that feeds a meteor shower by cracking and shedding dust in the Sun's heat, growing no tail of boiled-off ice.",
      "source": {
        "label": "NASA Science — Geminids",
        "url": "https://science.nasa.gov/solar-system/meteors-meteorites/geminids/"
      },
      "tags": [
        "l09p2",
        "geminids",
        "vocabulary",
        "derived"
      ],
      "whyOptions": [
        "Dwarf planet",
        "Fireball",
        "Ice giant"
      ],
      "whyCorrectIndex": 1,
      "uid": "1yodf84wjn1g"
    },
    {
      "id": "ast-f-iau-third-test",
      "shape": "fact",
      "title": "The Test That Decides",
      "body": "The **International Astronomical Union**'s 2006 definition sets three tests. A planet orbits the Sun. It has enough mass for its own gravity to pull it into a nearly round shape — **hydrostatic equilibrium**. And it has **cleared the neighbourhood** around its orbit. A body that passes the first two, fails the third and is not a satellite is a **dwarf planet**. The third test is not about size: it asks whether a body gravitationally dominates its orbital zone.",
      "factVariant": "image-heavy",
      "imageCaption": "Three tests, and only the third one ever decides anything.",
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "IAU planet definition three criteria flowchart",
        "imagePrompt": "Flat vector flowchart with three decision diamonds — orbits the Sun, rounded by its own gravity, cleared its neighbourhood — routing to planet, dwarf planet or small Solar System body.",
        "alt": "Flowchart of the IAU's three tests, with a body that passes the first two and fails the third landing on dwarf planet",
        "depictable": true,
        "allowGenerated": true
      },
      "source": {
        "label": "IAU — 2006 General Assembly: Result of the IAU Resolution votes (iau0603)",
        "url": "https://iauarchive.eso.org/news/pressreleases/detail/iau0603/"
      },
      "tags": [
        "l09p3",
        "iau-definition",
        "classification"
      ],
      "uid": "1egdotlzlmnkx"
    },
    {
      "id": "ast-f-eris-forced-the-vote",
      "shape": "fact",
      "title": "The Object That Forced It",
      "body": "In January 2005 Mike Brown, Chad Trujillo and David Rabinowitz identified **Eris** on images taken two years earlier. Timing its moon showed Eris is about **27 percent more massive than Pluto** — a body beyond Neptune that outweighed the ninth planet. Either Eris was a planet too, or the word needed a definition. The IAU chose the definition in 2006.",
      "source": {
        "label": "Caltech — The Dwarf Planet Known as Eris is More Massive than Pluto",
        "url": "https://www.caltech.edu/about/news/dwarf-planet-known-eris-more-massive-pluto-new-data-shows-1293"
      },
      "tags": [
        "l09p3",
        "eris",
        "discovery"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Eris and its moon Dysnomia Hubble image",
        "entityTerm": "Eris (dwarf planet)",
        "imagePrompt": "A Hubble-style image of the distant dwarf planet Eris as a bright point with the fainter point of its moon Dysnomia beside it against a sparse star field.",
        "alt": "Eris with its moon Dysnomia — the object beyond Neptune that turned out to outweigh Pluto",
        "depictable": true,
        "credit": "Wikipedia — Dysnomia (moon) · See Wikimedia Commons",
        "creditUrl": "https://en.wikipedia.org/wiki/Dysnomia_(moon)",
        "subject": "A Hubble/STScI frame on a red-noise starfield: a bright saturated blob labeled 'Eris' with an arrow, a small dot to its lower-left labeled 'Dysnomia' with an arrow, a green ellipse marked 'Orbit of Dysnomia', a distance scale ('43,000mi / 70,000km  1\"'), and N/E compass arrows — an annotated real Hu",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-eris-forced-the-vote.webp"
      },
      "uid": "1nmzc461rty76g"
    },
    {
      "id": "ast-f-pluto-unchanged",
      "shape": "fact",
      "title": "Nothing About Pluto Changed",
      "body": "**Pluto** orbits at an average of about **39 times** Earth's distance from the Sun, inside the **Kuiper Belt**, among objects that cross its path — so it fails the third test. The IAU recognises it as the prototype of the **trans-Neptunian objects**. Nothing about Pluto itself changed in 2006; what changed was what turned up next door.",
      "source": {
        "label": "IAU — 2006 General Assembly: Result of the IAU Resolution votes (iau0603)",
        "url": "https://iauarchive.eso.org/news/pressreleases/detail/iau0603/"
      },
      "tags": [
        "l09p3",
        "pluto",
        "classification"
      ],
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "Pluto orbit inclined and eccentric crossing Neptune orbit diagram",
        "imagePrompt": "Flat vector orbital diagram showing Neptune's near-circular orbit and Pluto's inclined, eccentric orbit crossing inside it, with other Kuiper Belt objects scattered along the same region.",
        "alt": "Diagram of Pluto's tilted, elongated orbit cutting inside Neptune's — a neighbourhood it has never cleared",
        "depictable": true,
        "allowGenerated": true
      },
      "uid": "1xxpywzm2x8nt"
    },
    {
      "id": "ast-f-five-dwarf-planets-list",
      "shape": "fact",
      "title": "Five Is Bookkeeping",
      "body": "Five bodies are officially recognised as dwarf planets. In order of distance from the Sun: **Ceres**, inside the asteroid belt, then **Pluto**, **Haumea**, **Makemake** and **Eris**, all beyond Neptune. Five is not a measurement — the IAU says there may be **over a hundred more** still to be found, and several known objects almost certainly qualify without having been designated.",
      "source": {
        "label": "NASA Science — Dwarf Planets",
        "url": "https://science.nasa.gov/dwarf-planets/"
      },
      "tags": [
        "l09p3",
        "dwarf-planets",
        "classification"
      ],
      "uid": "1821m47wdlitn"
    },
    {
      "id": "ast-p-small-solar-system-body",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Small Solar-System Body"
      },
      "sideB": {
        "modality": "text",
        "value": "Not a planet, not a dwarf planet, not a moon",
        "short": "not planet, dwarf or moon"
      },
      "source": {
        "label": "IAU — 2006 General Assembly: Result of the IAU Resolution votes (iau0603)",
        "url": "https://iauarchive.eso.org/news/pressreleases/detail/iau0603/"
      },
      "tags": [
        "l09p3",
        "iau-definition",
        "vocabulary"
      ],
      "uid": "ca2q791eapu3d"
    },
    {
      "id": "ast-d-dwarf-planet",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Dwarf planet"
      },
      "definition": {
        "modality": "text",
        "value": "A round body orbiting the Sun that has not cleared its orbital zone of other objects, and is not a moon of anything"
      },
      "curatedDistractors": [
        "Satellite",
        "Planetesimal",
        "Trans-Neptunian object"
      ],
      "source": {
        "label": "IAU — 2006 General Assembly: Result of the IAU Resolution votes (iau0603)",
        "url": "https://iauarchive.eso.org/news/pressreleases/detail/iau0603/"
      },
      "tags": [
        "l09p3",
        "iau-definition",
        "vocabulary"
      ],
      "uid": "1xgzej3ch6c5z"
    },
    {
      "id": "ast-q-pluto-reclassified-why",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Why is Pluto not counted among the eight planets?"
      },
      "options": [
        {
          "modality": "text",
          "value": "It is smaller than Earth's Moon"
        },
        {
          "modality": "text",
          "value": "It lies beyond Neptune"
        },
        {
          "modality": "text",
          "value": "New measurements shrank it"
        },
        {
          "modality": "text",
          "value": "It shares its orbital zone"
        }
      ],
      "correctIndex": 3,
      "explanation": "Pluto sits inside the Kuiper Belt among bodies that cross its path, so it fails the third IAU test. Being smaller than the Moon disqualifies nothing — there is no size rule, and every recognised dwarf planet is smaller. No measurement shrank it, and distance is not a criterion.",
      "source": {
        "label": "IAU — 2006 General Assembly: Result of the IAU Resolution votes (iau0603)",
        "url": "https://iauarchive.eso.org/news/pressreleases/detail/iau0603/"
      },
      "tags": [
        "l09p3",
        "pluto",
        "quiz"
      ],
      "uid": "1x8r1c2jli6is"
    },
    {
      "id": "ast-p-ceres-dwarf",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Ceres"
      },
      "sideB": {
        "modality": "text",
        "value": "The only dwarf planet inside the asteroid belt",
        "short": "the only one in the belt"
      },
      "source": {
        "label": "JPL Small-Body Database — 1 Ceres",
        "url": "https://ssd-api.jpl.nasa.gov/sbdb.api?sstr=1%20Ceres&phys-par=true"
      },
      "tags": [
        "l09p3",
        "dwarf-planets"
      ],
      "uid": "a3nceo1ytf15a"
    },
    {
      "id": "ast-p-pluto-dwarf",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Pluto"
      },
      "sideB": {
        "modality": "text",
        "value": "The IAU's prototype of the trans-Neptunian objects",
        "short": "prototype trans-Neptunian"
      },
      "source": {
        "label": "IAU — 2006 General Assembly: Result of the IAU Resolution votes (iau0603)",
        "url": "https://iauarchive.eso.org/news/pressreleases/detail/iau0603/"
      },
      "tags": [
        "l09p3",
        "dwarf-planets"
      ],
      "uid": "1oh09tt1gx1oxt"
    },
    {
      "id": "ast-p-haumea-dwarf",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Haumea"
      },
      "sideB": {
        "modality": "text",
        "value": "Spun to an egg shape by a four-hour rotation",
        "short": "four-hour spin, egg-shaped"
      },
      "source": {
        "label": "NASA Science — Haumea",
        "url": "https://science.nasa.gov/dwarf-planets/haumea/"
      },
      "tags": [
        "l09p3",
        "dwarf-planets"
      ],
      "uid": "agb4a8ryvpds"
    },
    {
      "id": "ast-p-makemake-dwarf",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Makemake"
      },
      "sideB": {
        "modality": "text",
        "value": "Second-brightest in the Kuiper Belt, from methane frost",
        "short": "2nd-brightest out there"
      },
      "source": {
        "label": "NASA Science — Makemake",
        "url": "https://science.nasa.gov/dwarf-planets/makemake/"
      },
      "tags": [
        "l09p3",
        "dwarf-planets"
      ],
      "uid": "juafo4qt37cu"
    },
    {
      "id": "ast-p-eris-dwarf",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Eris"
      },
      "sideB": {
        "modality": "text",
        "value": "27 percent heavier than the ninth planet; forced the 2006 vote",
        "short": "27% heavier; forced the vote"
      },
      "source": {
        "label": "Caltech — The Dwarf Planet Known as Eris is More Massive than Pluto",
        "url": "https://www.caltech.edu/about/news/dwarf-planet-known-eris-more-massive-pluto-new-data-shows-1293"
      },
      "tags": [
        "l09p3",
        "dwarf-planets"
      ],
      "uid": "95fknd1cboaj7"
    },
    {
      "id": "tfr-ast-d-dwarf-planet",
      "shape": "trueFalse",
      "derivedFrom": "ast-d-dwarf-planet",
      "statement": "Dwarf planet — a contracting ball of infalling gas that already glows from compression alone, before any fusion has started in its core.",
      "isTrue": false,
      "why": "A dwarf planet is a round body orbiting the Sun that has not cleared its orbital zone of other objects, and is not a moon of anything. A protostar is a stage in a star's life instead: a contracting ball of infalling gas that glows from compression alone, before fusion has started.",
      "source": {
        "label": "IAU — 2006 General Assembly: Result of the IAU Resolution votes (iau0603)",
        "url": "https://iauarchive.eso.org/news/pressreleases/detail/iau0603/"
      },
      "tags": [
        "l09p3",
        "iau-definition",
        "vocabulary",
        "derived"
      ],
      "whyOptions": [
        "Fireball",
        "Ice giant",
        "Protostar"
      ],
      "whyCorrectIndex": 2,
      "uid": "15so94r4cerpv"
    },
    {
      "id": "ast-f-kuiper-belt-icy-doughnut",
      "shape": "fact",
      "title": "Ice, Twenty Times Out",
      "body": "Beyond Neptune the disc of the Solar System does not stop — it thins. The **Kuiper Belt** is a thick, doughnut-shaped ring of icy leftovers whose main region runs from about **30 to 50 AU**: the asteroid belt's idea, twenty times further out and built of ice rather than rock. It is not a thin flat band, and it is not the Oort Cloud. For all that reach, NASA puts the whole belt's mass at **no more than about a tenth of Earth's**.",
      "factVariant": "image-heavy",
      "imageCaption": "A thick doughnut of ice beyond Neptune — not a thin band, and not the Oort Cloud.",
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "Kuiper Belt torus 30 to 50 AU diagram beyond Neptune orbit",
        "imagePrompt": "Flat vector diagram in oblique view showing the planetary orbits, Neptune at 30 AU, and a thick torus of icy bodies extending to 50 AU, with a scale note placing the Oort Cloud far beyond.",
        "alt": "Diagram of the Kuiper Belt as a thick doughnut from about 30 to 50 AU, well inside the far larger Oort Cloud",
        "depictable": true,
        "allowGenerated": true
      },
      "source": {
        "label": "NASA Science — Kuiper Belt Facts",
        "url": "https://science.nasa.gov/solar-system/kuiper-belt/facts/"
      },
      "tags": [
        "l10p1",
        "kuiper-belt",
        "structure"
      ],
      "uid": "11zsxh91az6fsx"
    },
    {
      "id": "ast-f-kuiper-belt-uncatalogued",
      "shape": "fact",
      "title": "Millions, Thousands Seen",
      "body": "The belt is a population, not a shortlist. NASA estimates **millions** of icy bodies out there, including **hundreds of thousands** wider than **100 km**. Only a **few thousand** trans-Neptunian objects have actually been observed and catalogued. The gap between those two numbers is a limit of telescopes, not of the belt — the famous names are simply the ones bright enough to have been found.",
      "source": {
        "label": "NASA Science — Kuiper Belt Facts",
        "url": "https://science.nasa.gov/solar-system/kuiper-belt/facts/"
      },
      "tags": [
        "l10p1",
        "kuiper-belt",
        "population"
      ],
      "uid": "1x1buw7qaockf"
    },
    {
      "id": "ast-f-kuiper-belt-albion-1992",
      "shape": "fact",
      "title": "Forty-One Years a Prediction",
      "body": "**Gerard Kuiper** proposed a belt of leftovers beyond Neptune in **1951**, and for forty-one years it stayed a prediction. Confirmation came in **1992**, when David Jewitt and Jane Luu found **1992 QB1** — later named **15760 Albion** — the first trans-Neptunian object discovered after Pluto and Charon. JPL puts its orbit at **44.1 AU** and about **293 years**. Almost everything we know about the outer Solar System has been found since.",
      "source": {
        "label": "JPL Small-Body Database — 15760 Albion (1992 QB1)",
        "url": "https://ssd-api.jpl.nasa.gov/sbdb.api?sstr=15760&full-prec=false"
      },
      "tags": [
        "l10p1",
        "kuiper-belt",
        "discovery"
      ],
      "uid": "1jgzjrx1w7dgnj"
    },
    {
      "id": "ast-f-pluto-belt-neighbours",
      "shape": "fact",
      "title": "Pluto Has Neighbours",
      "body": "**Pluto** was the first Kuiper Belt object ever discovered, in **1930**, though nobody could have known it then. NASA now describes it as a member of the belt: **2,377 km** across, averaging **39 AU** from the Sun, **248 years** to a lap. The 2006 reclassification was not a demotion invented by committee — it was the recognition that Pluto has company. **Eris**, about **2,400 km** at 68 AU, is so close in size that NASA's own pages leave the two effectively tied.",
      "source": {
        "label": "NASA Science — Pluto Facts",
        "url": "https://science.nasa.gov/dwarf-planets/pluto/facts/"
      },
      "tags": [
        "l10p1",
        "kuiper-belt",
        "pluto"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Pluto global colour mosaic New Horizons 2015",
        "entityTerm": "Pluto",
        "imagePrompt": "The New Horizons full-globe colour mosaic of Pluto showing the bright heart-shaped Sputnik Planitia against darker, redder cratered terrain.",
        "alt": "Pluto in full colour from New Horizons — the first Kuiper Belt object found, and far from the only one of its size",
        "depictable": true,
        "credit": "NASA/JHUAPL/SwRI · Public domain",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:Global_LORRI_mosaic_of_Pluto_in_true_colour.jpg",
        "subject": "NASA New Horizons LORRI global true-colour mosaic of Pluto, showing the heart-shaped Tombaugh Regio — this is exactly the 2015 New Horizons Pluto image the search term names, public domain via NASA/JHUAPL/SwRI",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-pluto-belt-neighbours.webp"
      },
      "uid": "giq7jo1svfw7q"
    },
    {
      "id": "ast-f-arrokoth-contact-binary",
      "shape": "fact",
      "title": "Two Lobes, Touching",
      "body": "On **1 January 2019** New Horizons passed within **3,538 km** of **Arrokoth**, a Kuiper Belt body about **35 km** end to end — the most distant object any spacecraft has reached. It is a **contact binary**: two rounded lobes resting against each other, poles and equators aligned. That alignment reads as a co-orbiting pair that merged gently at low speed, offered as support for the **pebble-cloud collapse** model of planet-building rather than a history of high-speed crashes. It is a model fitted to evidence.",
      "factVariant": "image-heavy",
      "imageCaption": "Two rounded lobes that settled together gently, not a wreck from a collision.",
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Arrokoth contact binary New Horizons flyby image",
        "entityTerm": "Arrokoth",
        "imagePrompt": "The New Horizons image of Arrokoth as a reddish snowman-shaped contact binary, two flattened lobes joined at a narrow neck.",
        "alt": "The New Horizons colour composite of the Kuiper Belt object Arrokoth (2014 MU69): a reddish-brown contact binary against black space, a larger flattened lobe below and a smaller rounder lobe…",
        "depictable": true,
        "subject": "The New Horizons colour composite of the Kuiper Belt object Arrokoth (2014 MU69): a reddish-brown contact binary against black space, a larger flattened lobe below and a smaller rounder lobe above, joined at a bright neck, with a large depression on the smaller lobe and small pits along the right-ha",
        "credit": "Wikimedia Commons · NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Inst · Public domain",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:UltimaThule_CA06_color_vertical.png",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-arrokoth-contact-binary.webp"
      },
      "source": {
        "label": "NASA Science — Arrokoth Facts",
        "url": "https://science.nasa.gov/solar-system/kuiper-belt/arrokoth-2014-mu69/facts/"
      },
      "tags": [
        "l10p1",
        "kuiper-belt",
        "arrokoth"
      ],
      "uid": "axoiy2266wm6"
    },
    {
      "id": "ast-p-plutinos-neptune-lock",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Plutinos"
      },
      "sideB": {
        "modality": "text",
        "value": "Belt objects sharing the 3:2 lock on Neptune",
        "short": "Sharing the 3:2 lock on Neptune"
      },
      "source": {
        "label": "NASA Science — Kuiper Belt Facts",
        "url": "https://science.nasa.gov/solar-system/kuiper-belt/facts/"
      },
      "tags": [
        "l10p1",
        "kuiper-belt",
        "resonance"
      ],
      "uid": "19a2dag42uz58"
    },
    {
      "id": "ast-p-kuiper-belt-mass",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "The Kuiper Belt's total mass"
      },
      "sideB": {
        "modality": "text",
        "value": "No more than about a tenth of Earth's"
      },
      "source": {
        "label": "NASA Science — Kuiper Belt Facts",
        "url": "https://science.nasa.gov/solar-system/kuiper-belt/facts/"
      },
      "tags": [
        "l10p1",
        "kuiper-belt",
        "mass"
      ],
      "uid": "10kni5vpeggtb"
    },
    {
      "id": "ast-d-trans-neptunian-object",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Trans-Neptunian object"
      },
      "definition": {
        "modality": "text",
        "value": "Any body catalogued on an orbit beyond the eighth planet's — the main belt, the scattered disc and everything past them, not just the crowded classical belt"
      },
      "curatedDistractors": [
        "Plutino",
        "Contact binary",
        "Detached"
      ],
      "source": {
        "label": "NASA Science — Kuiper Belt Facts",
        "url": "https://science.nasa.gov/solar-system/kuiper-belt/facts/"
      },
      "tags": [
        "l10p1",
        "kuiper-belt",
        "vocabulary"
      ],
      "uid": "1fsy95e67cmwi"
    },
    {
      "id": "ast-q-pluto-neptune-crossing",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Pluto's orbit crosses inside Neptune's. What timing keeps the two apart?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Neptune's gravity repels it"
        },
        {
          "modality": "text",
          "value": "They keep a 3:2 timing lock"
        },
        {
          "modality": "text",
          "value": "Their orbits are tilted apart"
        },
        {
          "modality": "text",
          "value": "Pluto is too small to matter"
        }
      ],
      "correctIndex": 1,
      "explanation": "Pluto goes round the Sun twice for every three Neptune orbits, so it always reaches the crossing point when Neptune is somewhere else. Tilt alone would not hold that pattern, size has nothing to do with whether two orbits meet, and gravity attracts.",
      "source": {
        "label": "NASA Science — Kuiper Belt Facts",
        "url": "https://science.nasa.gov/solar-system/kuiper-belt/facts/"
      },
      "tags": [
        "l10p1",
        "kuiper-belt",
        "resonance"
      ],
      "uid": "12pozvvbixlvt"
    },
    {
      "id": "ast-q-kuiper-belt-catalogue-gap",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "How many trans-Neptunian objects have astronomers actually catalogued?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Several billion"
        },
        {
          "modality": "text",
          "value": "Hundreds of thousands"
        },
        {
          "modality": "text",
          "value": "A few thousand"
        },
        {
          "modality": "text",
          "value": "About thirty thousand"
        }
      ],
      "correctIndex": 2,
      "explanation": "Only a few thousand trans-Neptunian objects have been observed and logged. NASA estimates millions are out there, hundreds of thousands of them wider than 100 km — but those are estimates, not sightings. Thirty thousand overshoots the catalogue; billions overshoot the estimate.",
      "source": {
        "label": "NASA Science — Kuiper Belt Facts",
        "url": "https://science.nasa.gov/solar-system/kuiper-belt/facts/"
      },
      "tags": [
        "l10p1",
        "kuiper-belt",
        "population"
      ],
      "uid": "1yslecg14wy0bk"
    },
    {
      "id": "czr-ast-d-trans-neptunian-object",
      "shape": "cloze",
      "derivedFrom": "ast-d-trans-neptunian-object",
      "template": "___ — Any body catalogued on an orbit beyond the eighth planet's — the main belt, the scattered disc and everything past them, not just the crowded classical belt",
      "answer": "Trans-Neptunian object",
      "distractors": [
        "Fireball",
        "Ice giant",
        "Rock comet"
      ],
      "explanation": "Trans-Neptunian object is any body catalogued on an orbit beyond the eighth planet's. Fireball, the closest of the alternatives, is a meteor brighter than magnitude −4, about as bright as Venus at its best.",
      "source": {
        "label": "NASA Science — Kuiper Belt Facts",
        "url": "https://science.nasa.gov/solar-system/kuiper-belt/facts/"
      },
      "tags": [
        "l10p1",
        "kuiper-belt",
        "vocabulary",
        "derived"
      ],
      "uid": "1b531r912x3wdj"
    },
    {
      "id": "ast-f-comet-nothing-burns",
      "shape": "fact",
      "title": "Nothing About It Burns",
      "body": "A comet is a **cosmic snowball** of frozen gases, rock and dust. Nothing about it is on fire: the glow is sunlight **scattered and re-emitted**, not combustion. Because a comet spends nearly all of its orbit in deep freeze far from the Sun, its material still holds the composition of the disc the planets formed from — each one is a **4.6-billion-year-old sample** that delivers itself to the inner Solar System.",
      "source": {
        "label": "NASA Science — Comets",
        "url": "https://science.nasa.gov/solar-system/comets/"
      },
      "tags": [
        "l10p2",
        "comets",
        "composition"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Comet NEOWISE 2020 over a dark landscape photograph",
        "entityTerm": "Comet NEOWISE",
        "imagePrompt": "A night photograph of a bright naked-eye comet with a long tail standing above a dark, simple horizon in deep twilight.",
        "alt": "A real night-sky photograph of Comet NEOWISE (small in frame, bright head with a short tail) low in a starry twilight sky above the silhouetted rock spires of the Trona Pinnacles, California, with…",
        "depictable": true,
        "credit": "Wikimedia Commons · RuggyBearLA · CC BY 2.0",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:Comet_NEOWISE_from_Trona_Pinnacles_-_50685737367.jpg",
        "subject": "A real night-sky photograph of Comet NEOWISE (small in frame, bright head with a short tail) low in a starry twilight sky above the silhouetted rock spires of the Trona Pinnacles, California, with town lights on the right horizon.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-comet-nothing-burns.webp"
      },
      "uid": "khwuq21g05pnc"
    },
    {
      "id": "ast-f-comet-coma-swells",
      "shape": "fact",
      "title": "Bigger Than Most Planets",
      "body": "The comet proper is the **nucleus**, usually under about **16 km** across — a frozen block the size of a town. What you see is not that. Sunlight drives gas and dust off the nucleus into a **coma**, a glowing head that can swell to **hundreds of thousands of kilometres**, larger than most planets. The bright fuzzy object in the sky is almost entirely material that has already left the comet.",
      "factVariant": "image-heavy",
      "imageCaption": "The solid comet is a town-sized block buried inside a head wider than a planet.",
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "comet anatomy diagram nucleus coma scale comparison",
        "imagePrompt": "Flat scale diagram: a tiny labelled nucleus at centre, the surrounding coma drawn to true relative scale at hundreds of thousands of kilometres, with a planet outlined for comparison.",
        "alt": "Diagram setting a comet's few-kilometre nucleus against the coma around it, which can outsize most planets",
        "depictable": true,
        "allowGenerated": true
      },
      "source": {
        "label": "NASA Space Place — What Is a Comet?",
        "url": "https://spaceplace.nasa.gov/comets/en/"
      },
      "tags": [
        "l10p2",
        "comets",
        "anatomy"
      ],
      "uid": "19sucpc1t38iws"
    },
    {
      "id": "ast-f-comet-two-tails",
      "shape": "fact",
      "title": "Two Tails, Two Forces",
      "body": "Bright comets show **two** tails. The bluish **ion tail** is charged gas swept out by the **solar wind** and points directly away from the Sun. The whitish **dust tail** is heavier grains pushed by the pressure of sunlight; they keep some of the comet's orbital motion, so that tail lags and curves. Neither is a wake. The direction is set by the Sun, not by the comet's travel — which is why on the outbound leg a comet moves **tail-first**.",
      "factVariant": "image-heavy",
      "imageCaption": "A straight blue streak and a broad white fan, both pointing away from the Sun.",
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "comet with separate blue ion tail and curved white dust tail photograph",
        "entityTerm": "Comet tail",
        "imagePrompt": "A photograph of a bright comet in which a straight, narrow, bluish ion tail and a broader, curved, whitish dust tail separate visibly from the same head.",
        "alt": "A comet showing both tails at once: a straight blue ion tail pointing away from the Sun and a curved white dust tail lagging behind",
        "depictable": true,
        "credit": "Wikipedia — Comet · See Wikimedia Commons",
        "creditUrl": "https://en.wikipedia.org/wiki/Comet",
        "subject": "Comet Hale-Bopp (1995O1), a genuine photograph (Wikipedia 'Comet' lead image) clearly showing two distinct tails: a broad, roughly straight whitish/pale-yellow dust-and-coma plume and a separate, finely-striated blue ion tail peeling off to the side against a starfield.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-comet-two-tails.webp"
      },
      "source": {
        "label": "NASA Space Place — What Is a Comet?",
        "url": "https://spaceplace.nasa.gov/comets/en/"
      },
      "tags": [
        "l10p2",
        "comets",
        "tails"
      ],
      "uid": "1gfl3xonhyx6u"
    },
    {
      "id": "ast-f-halley-not-a-timetable",
      "shape": "fact",
      "title": "An Average, Not a Timetable",
      "body": "**Halley's Comet** returns on average every **76 years** — an average, not a schedule: the giant planets tug the orbit and the real gap has run from **74 to 80 years**. Its first certain record is from **240 BCE**, it last rounded the Sun in February **1986**, and it returns in **2061**. Its shed dust rings the whole orbit, and Earth's path cuts that ring twice a year: the **Eta Aquarids** in May and the **Orionids** in October. A meteor shower does not mean a comet is nearby.",
      "source": {
        "label": "NASA Science — 1P/Halley",
        "url": "https://science.nasa.gov/solar-system/comets/1p-halley/"
      },
      "tags": [
        "l10p2",
        "comets",
        "halley"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Halley's Comet 1986 photograph",
        "entityTerm": "Halley’s Comet",
        "imagePrompt": "A 1986 astronomical photograph of Halley's Comet showing a bright condensed head and a broad tail against a star field.",
        "alt": "Halley's Comet during its 1986 apparition: a bright compact coma with a broad pinkish-violet tail streaming upward against a dark sky of short tricolour star trails, a colour composite of three…",
        "depictable": true,
        "credit": "ESO (Openverse) · by 4.0",
        "creditUrl": "https://commons.wikimedia.org/w/index.php?curid=26499690",
        "subject": "Halley's Comet during its 1986 apparition: a bright compact coma with a broad pinkish-violet tail streaming upward against a dark sky of short tricolour star trails, a colour composite of three photographic plates from ESO's GPO telescope.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-halley-not-a-timetable.webp"
      },
      "uid": "1s1fybv1jg9171"
    },
    {
      "id": "ast-f-comet-nucleus-size-brightness",
      "shape": "fact",
      "title": "Big Nucleus, Long Show",
      "body": "**Hale-Bopp** stayed visible to the naked eye for **18 months** across 1996 and 1997 — not because it came close to Earth, but because its nucleus is around **60 km** across, roughly four times Halley's. A great comet can be made by size and activity rather than by proximity — Hyakutake, in the same decade, was the other way round. **NEOWISE**, whose nucleus is about **5 km**, was found only three months before it brightened in 2020. That is normal: a long-period comet stays dark and tiny until the Sun heats it.",
      "source": {
        "label": "NASA Science — C/1995 O1 (Hale-Bopp)",
        "url": "https://science.nasa.gov/solar-system/comets/c-1995-o1-hale-bopp/"
      },
      "tags": [
        "l10p2",
        "comets",
        "brightness"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Comet Hale-Bopp 1997 bright naked eye comet photograph",
        "entityTerm": "Comet Hale–Bopp",
        "imagePrompt": "A 1997 photograph of Comet Hale-Bopp high in a dark sky, its brilliant head and long tails dominating the frame.",
        "alt": "Comet Hale-Bopp photographed in 1997 against a dense star field, showing its broad white-yellow dust tail and a separate blue ion tail fanning out to the left.",
        "depictable": true,
        "credit": "Wikipedia — Comet Hale–Bopp · See Wikimedia Commons",
        "creditUrl": "https://en.wikipedia.org/wiki/Comet_Hale%E2%80%93Bopp",
        "subject": "Comet Hale-Bopp photographed in 1997 against a dense star field, showing its broad white-yellow dust tail and a separate blue ion tail fanning out to the left.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-comet-nucleus-size-brightness.webp"
      },
      "uid": "1yq12lk8v16fe"
    },
    {
      "id": "ast-f-67p-rosetta-porous",
      "shape": "fact",
      "title": "A Comet Would Float",
      "body": "ESA's **Rosetta** made the first **rendezvous** with a comet, **67P**, in 2014; its lander **Philae** made the first landing that November, bouncing several times before it settled. 67P is two lobes joined at a neck and mostly empty — ESA quotes **70 to 80 percent** porosity and a density of **470 kg per cubic metre**, well under water's 1,000. Rosetta also measured its water: about **three times** the deuterium share of Earth's oceans, which weakened the case that comets filled our seas.",
      "source": {
        "label": "ESA — Getting to know Rosetta's comet",
        "url": "https://www.esa.int/Science_Exploration/Space_Science/Rosetta/Getting_to_know_Rosetta_s_comet"
      },
      "tags": [
        "l10p2",
        "comets",
        "rosetta"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "comet 67P Churyumov-Gerasimenko nucleus Rosetta image two lobes",
        "entityTerm": "67P/Churyumov–Gerasimenko",
        "imagePrompt": "A Rosetta close-range image of comet 67P's nucleus: two rounded lobes joined at a narrow neck, dusty grey surface with pits and boulders, against black space.",
        "alt": "The bilobed nucleus of comet 67P/Churyumov-Gerasimenko against black space, imaged by Rosetta's OSIRIS camera on 12 September 2014 — the small lobe (head) above, the large lobe (body) below…",
        "depictable": true,
        "credit": "europeanspaceagency (Openverse) · by-sa 4.0",
        "creditUrl": "https://www.flickr.com/photos/37472264@N04/16342569642",
        "subject": "The bilobed nucleus of comet 67P/Churyumov-Gerasimenko against black space, imaged by Rosetta's OSIRIS camera on 12 September 2014 — the small lobe (head) above, the large lobe (body) below, joined at the neck. White arrows label five surface regions A–E (Anuket, Ma'at, Hapi, Hathor and an eroding a",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-67p-rosetta-porous.webp"
      },
      "uid": "2yxuvj607221"
    },
    {
      "id": "ast-p-short-period-comets",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Short-period comets"
      },
      "sideB": {
        "modality": "text",
        "value": "One lap in under 200 years, out of the Kuiper Belt",
        "short": "Under 200 years, from the Kuiper Belt"
      },
      "source": {
        "label": "NASA Science — Comet Facts",
        "url": "https://science.nasa.gov/solar-system/comets/facts/"
      },
      "tags": [
        "l10p2",
        "comets",
        "orbits"
      ],
      "uid": "xrpeli4akrts"
    },
    {
      "id": "ast-p-comet-nucleus-town-sized",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "A comet's nucleus"
      },
      "sideB": {
        "modality": "text",
        "value": "The solid frozen block, usually under 16 km wide",
        "short": "A solid block under 16 km wide"
      },
      "source": {
        "label": "NASA Space Place — What Is a Comet?",
        "url": "https://spaceplace.nasa.gov/comets/en/"
      },
      "tags": [
        "l10p2",
        "comets",
        "anatomy"
      ],
      "uid": "1jc85ec134cfr2"
    },
    {
      "id": "ast-d-comet-coma",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Coma"
      },
      "definition": {
        "modality": "text",
        "value": "The glowing head of gas and dust already driven off a comet — hundreds of thousands of kilometres wide, and not the solid body buried inside it"
      },
      "curatedDistractors": [
        "Nucleus",
        "Ion tail",
        "Dust tail"
      ],
      "source": {
        "label": "NASA Science — Comet Facts",
        "url": "https://science.nasa.gov/solar-system/comets/facts/"
      },
      "tags": [
        "l10p2",
        "comets",
        "vocabulary"
      ],
      "uid": "1n85fyjo3s1g3"
    },
    {
      "id": "ast-q-comet-tail-direction",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Which way do a comet's tails point?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Away from the Sun"
        },
        {
          "modality": "text",
          "value": "Backwards along its path"
        },
        {
          "modality": "text",
          "value": "Straight toward the Sun"
        },
        {
          "modality": "text",
          "value": "Whichever way the nucleus spins"
        }
      ],
      "correctIndex": 0,
      "explanation": "Sunlight pressure and the solar wind push escaping gas and dust outward, so a tail always points away from the Sun — on the outbound leg a comet travels tail-first rather than trailing like smoke. Spin orients the jets, not the tail, and nothing drives material inward.",
      "source": {
        "label": "NASA Science — Comet Facts",
        "url": "https://science.nasa.gov/solar-system/comets/facts/"
      },
      "tags": [
        "l10p2",
        "comets",
        "tails"
      ],
      "uid": "1lpqlkc1dhlvla"
    },
    {
      "id": "ast-q-hale-bopp-brightness",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Why did Hale-Bopp stay a naked-eye object for 18 months?"
      },
      "options": [
        {
          "modality": "text",
          "value": "It sat inside our orbit a year"
        },
        {
          "modality": "text",
          "value": "It passed very close to Earth"
        },
        {
          "modality": "text",
          "value": "Its nucleus was unusually big"
        },
        {
          "modality": "text",
          "value": "It broke apart near the Sun"
        }
      ],
      "correctIndex": 2,
      "explanation": "At around 60 km across, roughly four times Halley's width, it stayed active far longer than most comets. It never came especially close to Earth, it did not break up, and it spent only a few months inside Earth's orbit — size and activity did the work.",
      "source": {
        "label": "NASA Science — C/1995 O1 (Hale-Bopp)",
        "url": "https://science.nasa.gov/solar-system/comets/c-1995-o1-hale-bopp/"
      },
      "tags": [
        "l10p2",
        "comets",
        "brightness"
      ],
      "uid": "1gzvpah1w8giwv"
    },
    {
      "id": "czr-ast-d-comet-coma",
      "shape": "cloze",
      "derivedFrom": "ast-d-comet-coma",
      "template": "___ — The glowing head of gas and dust already driven off a comet — hundreds of thousands of kilometres wide, and not the solid body buried inside it",
      "answer": "Coma",
      "distractors": [
        "Penumbra",
        "Coronal hole",
        "Exosphere"
      ],
      "explanation": "Coma is the glowing head of gas and dust already driven off a comet. Penumbra, the closest of the alternatives, is the outer part of a shadow, where the light source is partly blocked rather than hidden completely.",
      "source": {
        "label": "NASA Science — Comet Facts",
        "url": "https://science.nasa.gov/solar-system/comets/facts/"
      },
      "tags": [
        "l10p2",
        "comets",
        "vocabulary",
        "derived"
      ],
      "uid": "1fab5qc12zzxoi"
    },
    {
      "id": "ast-f-solar-system-three-edges",
      "shape": "fact",
      "title": "Three Edges, Three Answers",
      "body": "Ask where the Solar System ends and three answers are defensible, because they measure three different things. The **Kuiper Belt's outer edge** near **50 AU** is where the planet-forming disc thins out. The **heliopause** near **120 AU** is where the Sun's wind is stopped by the gas between the stars. The **Oort Cloud** is the third, and the one NASA states outright: the boundary is considered to lie **beyond its outer edge**, somewhere between 10,000 and 100,000 AU.",
      "factVariant": "image-heavy",
      "imageCaption": "Three candidate boundaries, each measuring something different — and each far apart.",
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "Solar System boundaries logarithmic scale diagram Kuiper Belt heliopause Oort Cloud",
        "imagePrompt": "Flat vector logarithmic distance scale from 1 AU outward, with the planets, the Kuiper Belt edge at 50 AU, the heliopause at 120 AU and the Oort Cloud's outer edge each marked and labelled.",
        "alt": "Logarithmic scale diagram marking three defensible edges: the Kuiper Belt near 50 AU, the heliopause near 120, and the Oort Cloud far beyond",
        "depictable": true,
        "allowGenerated": true
      },
      "source": {
        "label": "NASA/JPL — NASA's Voyager 2 Probe Enters Interstellar Space",
        "url": "https://www.jpl.nasa.gov/news/nasas-voyager-2-probe-enters-interstellar-space/"
      },
      "tags": [
        "l10p3",
        "outer-system",
        "boundaries"
      ],
      "uid": "t89zbl42snrt"
    },
    {
      "id": "ast-f-voyagers-heliopause-crossings",
      "shape": "fact",
      "title": "Crossing Is Not Leaving",
      "body": "**Voyager 1** crossed the heliopause on **25 August 2012** at about **122 AU**, the first spacecraft to leave the Sun's wind-blown bubble. **Voyager 2** crossed on **5 November 2018** — six years later, somewhere else, and at a different point in the Sun's roughly **11-year** activity cycle, over which the boundary itself moves. NASA gives Voyager 2's distance only as slightly more than 18 billion km, with no figure in AU. Neither probe has left the Solar System: the Sun's gravity still holds both.",
      "source": {
        "label": "NASA Science — Voyager Interstellar Mission",
        "url": "https://science.nasa.gov/mission/voyager/interstellar-mission/"
      },
      "tags": [
        "l10p3",
        "outer-system",
        "voyager"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Voyager spacecraft high gain antenna NASA",
        "entityTerm": "Voyager program",
        "imagePrompt": "A photograph of a Voyager spacecraft showing its large dish antenna, boom-mounted instruments and golden record, against a plain background.",
        "alt": "A Voyager spacecraft — the two machines that crossed the heliopause six years and a long way apart",
        "depictable": true,
        "credit": "Voyager_spacecraft_structure.jpg: NASA\nderivative work: Mirecki (talk) · Public domain",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:Voyager_spacecraft_structure.png",
        "subject": "A cleaner vector-redrawn derivative of the same full Voyager spacecraft structure diagram, English labels, public-domain NASA-sourced content",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-voyagers-heliopause-crossings.webp"
      },
      "uid": "qp3kxj1df4di5"
    },
    {
      "id": "ast-f-scattered-disc-and-sedna",
      "shape": "fact",
      "title": "Scattered, Then Detached",
      "body": "The belt does not simply stop. Beyond it lies the **scattered disc**: objects flung by Neptune onto stretched, tilted orbits that still dip back to about **30-35 AU** but reach outward towards **1,000 AU**, and thought to be the source of the short-period Jupiter-family comets. Further out sit **detached objects** such as **Sedna**, which never comes nearer than about **76 AU** — too far for Neptune to have put it there. That near point is firm; JPL carries Sedna out to about 1,010 AU, NASA's page to roughly 1,200.",
      "source": {
        "label": "NASA Science — Kuiper Belt Facts",
        "url": "https://science.nasa.gov/solar-system/kuiper-belt/facts/"
      },
      "tags": [
        "l10p3",
        "outer-system",
        "scattered-disc"
      ],
      "uid": "16eqr0i7mdu8q"
    },
    {
      "id": "ast-f-outer-system-light-time",
      "shape": "fact",
      "title": "Light Restores the Scale",
      "body": "AU stop meaning much past a hundred, so use light instead. Sunlight reaches Earth in about **8 minutes** and Neptune in about **4 hours** — the whole planetary system fits inside a four-hour light journey. It takes a further **10 to 28 days** to reach the Oort Cloud's inner edge, and as much as **a year and a half** to pass its outer one. The planets occupy the innermost fraction of one percent of the Solar System's radius.",
      "source": {
        "label": "NASA Science — Neptune Facts",
        "url": "https://science.nasa.gov/neptune/neptune-facts/"
      },
      "tags": [
        "l10p3",
        "outer-system",
        "scale"
      ],
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "Solar System distances measured in light travel time diagram minutes hours days",
        "imagePrompt": "Flat vector scale diagram along a single axis labelled in light-travel time, with Earth at 8 light-minutes, Neptune at about 4 light-hours, and the Oort Cloud's inner and outer edges at days and months.",
        "alt": "Diagram restating Solar System distances as light-travel time: eight minutes to Earth, four hours to Neptune, up to a year and a half to the Oort Cloud's edge",
        "depictable": true,
        "allowGenerated": true
      },
      "uid": "catek1ajms19"
    },
    {
      "id": "ast-d-heliopause-boundary",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Heliopause"
      },
      "definition": {
        "modality": "text",
        "value": "Where the Sun's outflowing wind is finally halted by the gas between the stars — a plasma transition, and not the end of the Sun's gravitational reach"
      },
      "curatedDistractors": [
        "Oort Cloud",
        "Scattered disc",
        "Kuiper Belt"
      ],
      "source": {
        "label": "NASA Science — Voyager Interstellar Mission",
        "url": "https://science.nasa.gov/mission/voyager/interstellar-mission/"
      },
      "tags": [
        "l10p3",
        "outer-system",
        "vocabulary"
      ],
      "uid": "d4qixv1dr56ut"
    },
    {
      "id": "ast-q-voyager-still-inside",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Voyager 1 crossed the heliopause in 2012. Has it left the Solar System?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Yes, it is beyond the planets"
        },
        {
          "modality": "text",
          "value": "No, the Sun still holds it"
        },
        {
          "modality": "text",
          "value": "Yes, it entered the Oort Cloud"
        },
        {
          "modality": "text",
          "value": "Yes, NASA says interstellar"
        }
      ],
      "correctIndex": 1,
      "explanation": "NASA does say Voyager 1 entered interstellar space — but that means it passed where the solar wind stops, not where the Sun's gravity stops, and it is still bound. Passing the planets is not the accepted edge, and the Oort Cloud is roughly 300 years away yet.",
      "source": {
        "label": "NASA Science — Voyager Interstellar Mission",
        "url": "https://science.nasa.gov/mission/voyager/interstellar-mission/"
      },
      "tags": [
        "l10p3",
        "outer-system",
        "voyager"
      ],
      "uid": "1sqefqc1rnqfuc"
    },
    {
      "id": "ast-q-nasa-outer-boundary",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Which boundary does NASA call the edge of the Solar System?"
      },
      "options": [
        {
          "modality": "text",
          "value": "The Kuiper Belt's outer edge"
        },
        {
          "modality": "text",
          "value": "The far side of the Oort Cloud"
        },
        {
          "modality": "text",
          "value": "Neptune's orbit"
        },
        {
          "modality": "text",
          "value": "The heliopause"
        }
      ],
      "correctIndex": 1,
      "explanation": "NASA states the boundary is considered to lie beyond the outer edge of the Oort Cloud. The heliopause near 120 AU only marks where the solar wind stops, the belt near 50 AU is where the planet-forming disc thins, and past Neptune lie the scattered disc and more.",
      "source": {
        "label": "NASA/JPL — NASA's Voyager 2 Probe Enters Interstellar Space",
        "url": "https://www.jpl.nasa.gov/news/nasas-voyager-2-probe-enters-interstellar-space/"
      },
      "tags": [
        "l10p3",
        "outer-system",
        "boundaries"
      ],
      "uid": "1lw0z36k568sw"
    },
    {
      "id": "ast-n-au-kuiper-belt-edge",
      "shape": "numeric",
      "prompt": {
        "modality": "text",
        "value": "The Kuiper Belt's main outer edge"
      },
      "value": 50,
      "unit": "AU",
      "tolerance": 5,
      "source": {
        "label": "NASA Science — Kuiper Belt Facts",
        "url": "https://science.nasa.gov/solar-system/kuiper-belt/facts/"
      },
      "tags": [
        "l10p3",
        "outer-system",
        "distance"
      ],
      "uid": "1i0q3tq1k3cicy"
    },
    {
      "id": "ast-n-au-sedna-perihelion",
      "shape": "numeric",
      "prompt": {
        "modality": "text",
        "value": "Sedna at its closest to the Sun"
      },
      "value": 76,
      "unit": "AU",
      "tolerance": 2,
      "source": {
        "label": "JPL Small-Body Database — 90377 Sedna (2003 VB12)",
        "url": "https://ssd-api.jpl.nasa.gov/sbdb.api?sstr=90377&full-prec=true"
      },
      "tags": [
        "l10p3",
        "outer-system",
        "distance"
      ],
      "uid": "y6ov2qz0ewj2"
    },
    {
      "id": "ast-n-au-voyager1-heliopause",
      "shape": "numeric",
      "prompt": {
        "modality": "text",
        "value": "Voyager 1's distance when it crossed the heliopause"
      },
      "value": 122,
      "unit": "AU",
      "tolerance": 3,
      "source": {
        "label": "NASA Science — Voyager Interstellar Mission",
        "url": "https://science.nasa.gov/mission/voyager/interstellar-mission/"
      },
      "tags": [
        "l10p3",
        "outer-system",
        "distance"
      ],
      "uid": "1w73dvq85cf2k"
    },
    {
      "id": "ast-n-au-scattered-disc-reach",
      "shape": "numeric",
      "prompt": {
        "modality": "text",
        "value": "How far out the scattered disc reaches"
      },
      "value": 1000,
      "unit": "AU",
      "tolerance": 200,
      "source": {
        "label": "NASA Science — Kuiper Belt Facts",
        "url": "https://science.nasa.gov/solar-system/kuiper-belt/facts/"
      },
      "tags": [
        "l10p3",
        "outer-system",
        "distance"
      ],
      "uid": "fqxvqofd6p3m"
    },
    {
      "id": "ast-n-au-oort-inner-near",
      "shape": "numeric",
      "prompt": {
        "modality": "text",
        "value": "The Oort Cloud's inner edge, near end of NASA's main range"
      },
      "value": 2000,
      "unit": "AU",
      "tolerance": 300,
      "source": {
        "label": "NASA Science — Oort Cloud Facts",
        "url": "https://science.nasa.gov/solar-system/oort-cloud/facts/"
      },
      "tags": [
        "l10p3",
        "outer-system",
        "distance"
      ],
      "uid": "1n7ajdu14lb0ro"
    },
    {
      "id": "ast-n-au-oort-inner-far",
      "shape": "numeric",
      "prompt": {
        "modality": "text",
        "value": "The Oort Cloud's inner edge, far end of NASA's main range"
      },
      "value": 5000,
      "unit": "AU",
      "tolerance": 500,
      "source": {
        "label": "NASA Science — Oort Cloud Facts",
        "url": "https://science.nasa.gov/solar-system/oort-cloud/facts/"
      },
      "tags": [
        "l10p3",
        "outer-system",
        "distance"
      ],
      "uid": "132noqkyrop58"
    },
    {
      "id": "ast-n-au-oort-outer-edge",
      "shape": "numeric",
      "prompt": {
        "modality": "text",
        "value": "The Oort Cloud's outer edge, far end of NASA's range"
      },
      "value": 100000,
      "unit": "AU",
      "tolerance": 10000,
      "source": {
        "label": "NASA Science — Oort Cloud Facts",
        "url": "https://science.nasa.gov/solar-system/oort-cloud/facts/"
      },
      "tags": [
        "l10p3",
        "outer-system",
        "distance"
      ],
      "uid": "ic75awlucoyq"
    },
    {
      "id": "tfr-ast-d-heliopause-boundary",
      "shape": "trueFalse",
      "derivedFrom": "ast-d-heliopause-boundary",
      "statement": "Heliopause — where the Sun's outflowing wind is finally halted by the gas between the stars.",
      "isTrue": true,
      "why": "A coma is the glowing head of gas and dust already driven off a comet. The heliopause is a boundary far out in the Solar System: where the Sun's outflowing wind is finally halted by the gas between the stars, a line both Voyager probes have now crossed.",
      "source": {
        "label": "NASA Science — Voyager Interstellar Mission",
        "url": "https://science.nasa.gov/mission/voyager/interstellar-mission/"
      },
      "tags": [
        "l10p3",
        "outer-system",
        "vocabulary",
        "derived"
      ],
      "uid": "174bcq1dkvesv"
    },
    {
      "id": "ast-f-solar-system-one-collapse",
      "shape": "fact",
      "title": "One Cloud, One Birthday",
      "body": "The Sun, the planets, the moons, the asteroids and the comets all date from a single event about **4.6 billion years ago**, when a dense cloud of interstellar gas and dust collapsed under its own gravity. The Sun did not form first and then gather up planets that were already wandering about — everything here condensed out of the same collapse.",
      "source": {
        "label": "NASA Science — Solar System Facts",
        "url": "https://science.nasa.gov/solar-system/solar-system-facts/"
      },
      "tags": [
        "l11p1",
        "formation",
        "solar-nebula"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Barnard 68 Bok globule dark dense molecular cloud core",
        "entityTerm": "Bok globule",
        "imagePrompt": "A photograph of a compact, opaque dark globule silhouetted against a dense field of background stars, its edges sharply defined.",
        "alt": "A Bok globule: a dense, cold cloud of gas and dust of the kind whose collapse made the Sun and everything with it",
        "depictable": true,
        "credit": "Wikipedia — Barnard 68 · See Wikimedia Commons",
        "creditUrl": "https://en.wikipedia.org/wiki/Barnard_68",
        "subject": "Barnard 68 (Wikipedia's own article on it): a dense, round, black cloud of dust and gas completely blotting out the starfield behind it — the archetypal dark Bok globule / molecular-cloud core",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-solar-system-one-collapse.webp"
      },
      "uid": "1rmowem1e43e90"
    },
    {
      "id": "ast-f-solar-nebula-flat-disc",
      "shape": "fact",
      "title": "Why The Orbits Line Up",
      "body": "A cloud rotating even slightly spins **faster as it shrinks**, and a spinning collapsing cloud flattens. The result was the **solar nebula**: a disc of gas and dust around the young Sun. That is why the planets today all orbit in **nearly the same plane** and in the **same direction** — they were assembled from a spinning plate and still carry its motion. Randomly tilted, randomly directed orbits were never on the table.",
      "factVariant": "image-heavy",
      "imageCaption": "The flat, one-way layout of the Solar System is a fossil of the disc it condensed out of.",
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "rotating collapsing cloud flattening into a protoplanetary disc diagram",
        "imagePrompt": "Flat vector three-stage diagram: a slowly rotating spherical cloud, the same cloud contracting and spinning faster, and the resulting flattened disc with a young star at its centre.",
        "alt": "Diagram of a slowly rotating cloud spinning faster as it shrinks and flattening into a disc — which is why the orbits line up",
        "depictable": true,
        "allowGenerated": true
      },
      "source": {
        "label": "ESA — Comets and how the Solar System formed",
        "url": "https://www.esa.int/ESA_Multimedia/Images/2013/12/Comets_and_how_the_Solar_System_formed"
      },
      "tags": [
        "l11p1",
        "formation",
        "solar-nebula"
      ],
      "uid": "116o6txmqbjer"
    },
    {
      "id": "ast-f-supernova-isotope-clue",
      "shape": "fact",
      "title": "Isotopes With A Deadline",
      "body": "A cold cloud can sit for a very long time without collapsing, so something probably pushed. The evidence for a dying star nearby is chemical: the oldest meteorites hold the decay products of **aluminium-26** and **iron-60**. Iron-60's half-life is **2.60 million years** — far too short to have survived from the early universe, so it must have been made shortly before the Solar System's first solids froze. It is made in quantity essentially only inside massive stars. A strong argument, not an eyewitness.",
      "source": {
        "label": "Physics World — Nailing the half-life of iron-60 (Wallner et al. 2015)",
        "url": "https://physicsworld.com/a/nailing-the-half-life-of-iron-60/"
      },
      "tags": [
        "l11p1",
        "formation",
        "isotopes"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "calcium aluminium rich inclusion in a primitive chondrite meteorite thin section",
        "entityTerm": "Calcium–aluminium-rich inclusion",
        "imagePrompt": "A polarised-light photomicrograph of a chondrite meteorite thin section showing rounded chondrules and irregular white calcium-aluminium-rich inclusions in a dark matrix.",
        "alt": "A deep-sky astrophotograph of the supernova remnant CTB 1 (Abell 85) in Cassiopeia: a roughly spherical shell of red hydrogen-alpha filaments with a faint blue-green rim, set against a dense…",
        "depictable": true,
        "subject": "A deep-sky astrophotograph of the supernova remnant CTB 1 (Abell 85) in Cassiopeia: a roughly spherical shell of red hydrogen-alpha filaments with a faint blue-green rim, set against a dense starfield and diffuse red nebulosity. No meteorite or thin section is in frame.",
        "credit": "Pexels · A detailed image of a supernova remnant showcasing intricate cosmic patterns and celestial beauty.",
        "creditUrl": "https://www.pexels.com/photo/ctb-1-supernova-remnant-in-space-19798813/",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-supernova-isotope-clue.webp"
      },
      "uid": "5yyf2bvx6ok9"
    },
    {
      "id": "ast-f-frost-line-sorted-system",
      "shape": "fact",
      "title": "The Boundary That Sorted Everything",
      "body": "Inside the frost line only **rock and metal** could stay solid, so the inner planets had very little to work with and came out small. Beyond it water froze into ice in bulk — and further out still, methane and ammonia — giving those bodies vastly more solid material and letting them grow into giants. That one boundary is why the four inner planets are **terrestrial**, with surfaces you could stand on, and the four outer ones have **no ground at all**. Size was not luck.",
      "source": {
        "label": "NASA Space Place — How Did the Solar System Form?",
        "url": "https://spaceplace.nasa.gov/solar-system-formation/en/"
      },
      "tags": [
        "l11p1",
        "frost-line",
        "planets"
      ],
      "uid": "1ho1veyruirps"
    },
    {
      "id": "ast-f-sun-holds-99-8-percent",
      "shape": "fact",
      "title": "One Star, Plus Debris",
      "body": "The Sun holds **99.8 per cent** of the Solar System's mass. Every planet, every moon, the asteroid belt, the Kuiper Belt and all the comets together make up the remaining **fifth of one per cent**. Jupiter, the largest planet, is about a thousandth of the Sun's mass. That single number is why the Sun's gravity, and not any planet's, governs almost every orbit in the system.",
      "source": {
        "label": "NASA Science — Sun Facts",
        "url": "https://science.nasa.gov/sun/facts/"
      },
      "tags": [
        "l11p1",
        "sun",
        "mass"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "the full solar disc dominating a black field white light photograph",
        "entityTerm": "Sun",
        "imagePrompt": "A white-light photograph of the Sun's full disc, sunspot groups visible, filling most of an otherwise empty black frame.",
        "alt": "A full solar disc against a black sky, photographed in filtered white light, with several dark sunspot groups visible on the pale orange photosphere — the Sun alone in the frame.",
        "depictable": true,
        "credit": "Pexels · Detailed image of the sun showing visible sunspots on its surface.",
        "creditUrl": "https://www.pexels.com/photo/close-up-view-of-the-sun-with-sunspots-29893783/",
        "subject": "A full solar disc against a black sky, photographed in filtered white light, with several dark sunspot groups visible on the pale orange photosphere — the Sun alone in the frame.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-sun-holds-99-8-percent.webp"
      },
      "uid": "1w80wo7mf9i9j"
    },
    {
      "id": "ast-d-frost-line",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Frost line"
      },
      "definition": {
        "modality": "text",
        "value": "The distance from a young star beyond which water stops being vapour and freezes into solid grains — a temperature boundary that travels, not a fixed wall"
      },
      "source": {
        "label": "ESO — Stellar Outburst Brings Water Snow Line Into View",
        "url": "https://www.eso.org/public/unitedkingdom/news/eso1626/"
      },
      "tags": [
        "l11p1",
        "frost-line",
        "disc"
      ],
      "uid": "rik6yi184hpge"
    },
    {
      "id": "ast-p-planetesimals-formation",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Planetesimals"
      },
      "sideB": {
        "modality": "text",
        "value": "Kilometre-sized clumps built from dust that stuck together",
        "short": "Kilometre-sized clumps of stuck dust"
      },
      "source": {
        "label": "NASA Space Place — How Did the Solar System Form?",
        "url": "https://spaceplace.nasa.gov/solar-system-formation/en/"
      },
      "tags": [
        "l11p1",
        "accretion",
        "planetesimals"
      ],
      "uid": "1j0xr4nj0b7nn"
    },
    {
      "id": "ast-p-belts-unused-material",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "The asteroid and Kuiper Belts"
      },
      "sideB": {
        "modality": "text",
        "value": "Original building material never used — rockier close in, icier further out",
        "short": "Building material never used"
      },
      "source": {
        "label": "NASA Science — Asteroid Facts",
        "url": "https://science.nasa.gov/solar-system/asteroids/facts/"
      },
      "tags": [
        "l11p1",
        "frost-line",
        "leftovers"
      ],
      "uid": "1sjbl0w310d28"
    },
    {
      "id": "ast-q-inner-planets-small",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Why are the planets nearest the Sun so small?"
      },
      "options": [
        {
          "modality": "text",
          "value": "They had less time to grow"
        },
        {
          "modality": "text",
          "value": "Ice was scarce all over the disc"
        },
        {
          "modality": "text",
          "value": "Only rock and metal stayed solid"
        },
        {
          "modality": "text",
          "value": "The solar wind stripped them"
        }
      ],
      "correctIndex": 2,
      "explanation": "Inside the frost line only rock and metal stayed solid, so there was very little to build with. They had the same time as everyone else; the solar wind strips atmospheres rather than rock; and ice was abundant beyond that boundary rather than scarce everywhere.",
      "source": {
        "label": "NASA Space Place — How Did the Solar System Form?",
        "url": "https://spaceplace.nasa.gov/solar-system-formation/en/"
      },
      "tags": [
        "l11p1",
        "frost-line",
        "planets"
      ],
      "uid": "5uojltfpy1ur"
    },
    {
      "id": "ast-q-supernova-trigger-evidence",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "What supports the idea that a nearby exploding star squeezed the cloud?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Decayed isotopes in meteorites"
        },
        {
          "modality": "text",
          "value": "The Sun's 99.8 per cent share"
        },
        {
          "modality": "text",
          "value": "The flat plane of the orbits"
        },
        {
          "modality": "text",
          "value": "The Sun's high metal content"
        }
      ],
      "correctIndex": 0,
      "explanation": "Aluminium-26 and iron-60 decay far too fast to be primordial, so their daughter products date their making to just before the first solids froze. High metal content shows earlier generations of stars in general, not one nearby blast. The flat plane records the disc.",
      "source": {
        "label": "Physics World — Nailing the half-life of iron-60 (Wallner et al. 2015)",
        "url": "https://physicsworld.com/a/nailing-the-half-life-of-iron-60/"
      },
      "tags": [
        "l11p1",
        "formation",
        "isotopes"
      ],
      "uid": "1xwaw7a8ww3s"
    },
    {
      "id": "czr-ast-d-frost-line",
      "shape": "cloze",
      "derivedFrom": "ast-d-frost-line",
      "template": "___ — The distance from a young star beyond which water stops being vapour and freezes into solid grains — a temperature boundary that travels, not a fixed wall",
      "answer": "Frost line",
      "distractors": [
        "Airmass",
        "Apparent magnitude",
        "Solar mass"
      ],
      "explanation": "Frost line is the distance from a young star beyond which water stops being vapour and freezes into solid grains. Airmass, the closest of the alternatives, is how much atmosphere a beam crosses on its way down.",
      "source": {
        "label": "ESO — Stellar Outburst Brings Water Snow Line Into View",
        "url": "https://www.eso.org/public/unitedkingdom/news/eso1626/"
      },
      "tags": [
        "l11p1",
        "frost-line",
        "disc",
        "derived"
      ],
      "uid": "gkgmm15iie6b"
    },
    {
      "id": "ast-f-angular-momentum-problem",
      "shape": "fact",
      "title": "Mass Here, Spin There",
      "body": "That 99.8 per cent creates a genuine puzzle, still open: the **angular momentum problem**. The Sun holds nearly all the mass but only a small share of the system's spin — roughly **99 per cent** of the angular momentum sits in the planets' orbits, most of it in the outer planets'. A cloud that simply fell inwards would have left the Sun spinning near break-up. **Magnetic braking** by the young Sun's wind is the favoured way it shed the excess: a proposed mechanism, not something observed.",
      "source": {
        "label": "University of Oregon, AST 121 — Origin of the Solar System",
        "url": "https://pages.uoregon.edu/jschombe/ast121/lectures/lec23.html"
      },
      "tags": [
        "l11p2",
        "angular-momentum",
        "sun"
      ],
      "uid": "16iug71b1xhvn"
    },
    {
      "id": "ast-f-disc-in-100000-years",
      "shape": "fact",
      "title": "Caught In The Act",
      "body": "Theory puts the flattening of cloud into disc at roughly the first **100,000 years** — and telescopes agree. **L1527**, a protostar in Taurus imaged by NASA's Webb telescope, is only about 100,000 years old and already carries a dark accretion disc **about the size of our Solar System**. You do not have to take the disc on trust: the model's first step is something we can watch happening elsewhere right now.",
      "factVariant": "image-heavy",
      "imageCaption": "L1527 is about 100,000 years old and already has a disc the size of our Solar System.",
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "L1527 protostar and accretion disc Webb infrared image",
        "entityTerm": "L1527",
        "imagePrompt": "The Webb infrared image of L1527: an hourglass of orange and blue nebulosity with a dark horizontal band across the centre marking the edge-on accretion disc.",
        "alt": "The JWST MIRI image of the protostar L1527 in Taurus: a bright central point source with a dark, reddish edge-on accretion disc across its waist and blue-purple bipolar outflow lobes flaring above…",
        "depictable": true,
        "credit": "NASA, ESA, CSA, STScI · CC BY 4.0",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:L1527_(MIRI_image)_(L1527-1).jpg",
        "subject": "The JWST MIRI image of the protostar L1527 in Taurus: a bright central point source with a dark, reddish edge-on accretion disc across its waist and blue-purple bipolar outflow lobes flaring above and below in an hourglass shape, against a black star field.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-disc-in-100000-years.webp"
      },
      "source": {
        "label": "NASA Science / Webb — Webb Catches Fiery Hourglass as New Star Forms",
        "url": "https://science.nasa.gov/missions/webb/nasas-webb-catches-fiery-hourglass-as-new-star-forms/"
      },
      "tags": [
        "l11p2",
        "disc",
        "timeline"
      ],
      "uid": "z2w3bwr1a8gs"
    },
    {
      "id": "ast-f-disc-gas-deadline",
      "shape": "fact",
      "title": "Three Million Years, Then Nothing",
      "body": "Dating of meteorite grains shows the disc was making solids for only about **3 million years**, and the young Sun's wind and radiation had cleared the remaining gas within roughly **3 to 10 million years**. The **Atacama Large Millimeter Array (ALMA)**'s picture of **HL Tauri** — a star no more than a million years old, already carved into concentric rings separated by gaps — shows how fast the process runs. That deadline is why there are only four giants: anything that grew large later found nothing left to grab.",
      "source": {
        "label": "Connelly et al. 2012, Science — Absolute chronology of solids in the solar protoplanetary disk",
        "url": "https://pubmed.ncbi.nlm.nih.gov/23118187/"
      },
      "tags": [
        "l11p2",
        "disc",
        "timeline"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "HL Tauri protoplanetary disc ALMA image rings and gaps",
        "entityTerm": "HL Tauri",
        "imagePrompt": "The ALMA millimetre-wave image of the HL Tauri disc as a bright orange ringed disc with sharp dark concentric gaps, against black.",
        "alt": "The ALMA image of HL Tauri: a young protoplanetary disc already carved into concentric rings and gaps",
        "depictable": true,
        "credit": "ALMA (ESO/NAOJ/NRAO) · CC BY 4.0",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:HL_Tau_protoplanetary_disk.jpg",
        "subject": "The canonical ALMA HL Tauri image direct from its own Wikimedia Commons file page: a bright yellow core inside an orange/red disc cut by several dark concentric gaps into bright rings, explicitly CC BY 4.0 and credited to ALMA (ESO/NAOJ/NRAO).",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-disc-gas-deadline.webp"
      },
      "uid": "5i1sutrytnqn"
    },
    {
      "id": "ast-f-jupiter-formed-first",
      "shape": "fact",
      "title": "Jupiter Went First",
      "body": "An isotopic study of iron meteorites by **Kruijer and colleagues (2017)** found two chemically distinct populations that stayed separated for millions of years. The simplest explanation is a large body already massive enough to keep them apart: Jupiter's core reaching about **20 Earth masses** within the first million years, splitting the disc in two. That is one research group's inference, not settled history — but on this reading the planets did not form in the order they orbit.",
      "source": {
        "label": "University of Münster — Jupiter is the oldest planet of the Solar System (Kruijer et al. 2017)",
        "url": "https://www.uni-muenster.de/news/view.php?cmdid=8953"
      },
      "tags": [
        "l11p2",
        "jupiter",
        "timeline"
      ],
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "early Solar System disc split into two isotopic reservoirs by Jupiter diagram",
        "imagePrompt": "Flat vector diagram of the young solar nebula with a growing Jupiter core partway out, holding an inner and an outer reservoir of material separate on either side of its orbit.",
        "alt": "Diagram of a young Jupiter's core dividing the disc, keeping two populations of material chemically apart",
        "depictable": true,
        "allowGenerated": true
      },
      "uid": "1veqdn4122efjq"
    },
    {
      "id": "ast-f-moon-giant-impact",
      "shape": "fact",
      "title": "Wreckage That Became A Moon",
      "body": "NASA's account is that around **4.5 billion years ago** something roughly the size of Mars — or a series of objects — struck the young Earth and threw enough molten and vaporised debris into orbit to build the **Moon**, about **60 million years** after the Solar System began forming. The Apollo rocks agree: lunar basalts closely resemble Earth's mantle basalts, and lunar rock is **depleted in the elements that boil off when heated**. Similar, not identical — the best explanation, not a closed case.",
      "source": {
        "label": "NASA Science — How the Moon Formed",
        "url": "https://science.nasa.gov/moon/formation/"
      },
      "tags": [
        "l11p2",
        "moon",
        "impact"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Apollo lunar basalt sample in the lunar sample laboratory",
        "entityTerm": "Moon rock",
        "imagePrompt": "A studio photograph of an Apollo lunar basalt sample: a dark vesicular rock on a clean laboratory surface with a scale cube beside it.",
        "alt": "A full Moon photographed in a black night sky, showing the familiar near-side maria pattern of Earth's Moon;",
        "depictable": true,
        "subject": "A full Moon photographed in a black night sky, showing the familiar near-side maria pattern of Earth's Moon; the disc is sharp but small and sits off-centre in the upper-left of an otherwise empty frame. It is not a rock sample.",
        "credit": "Pexels · A detailed photograph of a full moon in the night sky, captured from Israel.",
        "creditUrl": "https://www.pexels.com/photo/full-moon-in-night-sky-over-israel-30264827/",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-moon-giant-impact.webp"
      },
      "uid": "17tx2i31iozfg1"
    },
    {
      "id": "ast-d-radiometric-dating",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Radiometric dating"
      },
      "definition": {
        "modality": "text",
        "value": "Reading an age from the ratio of a decaying parent isotope to its daughter — it times when a rock last closed up, not when its atoms were made"
      },
      "source": {
        "label": "USGS — Geologic Age: Using Radioactive Decay to Determine Geologic Age",
        "url": "https://www.usgs.gov/educational-resources/geologic-age-using-radioactive-decay-determine-geologic-age"
      },
      "tags": [
        "l11p2",
        "dating",
        "method"
      ],
      "uid": "17p36ijoli4zp"
    },
    {
      "id": "ast-p-oldest-dated-solids",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "The oldest dated solids"
      },
      "sideB": {
        "modality": "text",
        "value": "Calcium-aluminium-rich specks in meteorites, 4,567 million years",
        "short": "4,567 million years old"
      },
      "source": {
        "label": "Connelly et al. 2012, Science — Absolute chronology of solids in the solar protoplanetary disk",
        "url": "https://pubmed.ncbi.nlm.nih.gov/23118187/"
      },
      "tags": [
        "l11p2",
        "dating",
        "meteorites"
      ],
      "uid": "vb2n3q1e6m2u4"
    },
    {
      "id": "ast-q-earth-younger-than-meteorites",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Why does Earth date younger than the oldest meteorite grains?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Those grains predate the system"
        },
        {
          "modality": "text",
          "value": "Decay rates changed over time"
        },
        {
          "modality": "text",
          "value": "It formed from a later cloud"
        },
        {
          "modality": "text",
          "value": "It took longer to finish forming"
        }
      ],
      "correctIndex": 3,
      "explanation": "The first solids froze at 4.567 billion years; Earth needed tens of millions of years of collisions after that, giving about 4.5 billion. Melting resets one rock's clock, not a planet's formation date; the grains formed inside the same event, not before it; and decay rates are fixed.",
      "source": {
        "label": "NASA Science — Earth Facts",
        "url": "https://science.nasa.gov/earth/facts/"
      },
      "tags": [
        "l11p2",
        "earth",
        "dating"
      ],
      "uid": "gwuzia9k5bsa"
    },
    {
      "id": "ast-q-giant-impact-awkward",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "What makes the giant-impact story awkward rather than closed?"
      },
      "options": [
        {
          "modality": "text",
          "value": "It matches Earth's rock too well"
        },
        {
          "modality": "text",
          "value": "Lunar rock is rich in volatiles"
        },
        {
          "modality": "text",
          "value": "The Moon has no magma history"
        },
        {
          "modality": "text",
          "value": "No impactor debris on Earth"
        }
      ],
      "correctIndex": 0,
      "explanation": "A Mars-sized impactor should have left the Moon made mostly of the impactor, yet the two are nearly identical isotopically. Debris from it was never expected to survive on Earth. The Moon does have a magma-ocean history, and its rocks are notably POOR in volatiles.",
      "source": {
        "label": "NASA Science — How the Moon Formed",
        "url": "https://science.nasa.gov/moon/formation/"
      },
      "tags": [
        "l11p2",
        "moon",
        "impact"
      ],
      "uid": "c0h1mu1vttf58"
    },
    {
      "id": "ast-f-late-heavy-bombardment-contested",
      "shape": "fact",
      "title": "A Textbook Fact In Trouble",
      "body": "The **Late Heavy Bombardment** — a proposed spike of impacts across the inner Solar System around **3.9 billion years ago** — is now seriously contested. It was inferred from a cluster of Apollo sample ages, and a 2016 analysis showed a steadily declining impact rate produces that same apparent cluster. A 2017 review found the lunar record fits **prolonged bombardment from about 4.2 to 3.4 billion years ago** instead. The craters are not in doubt; the sudden late surge is.",
      "source": {
        "label": "Boehnke & Harrison 2016, PNAS — Illusory Late Heavy Bombardments",
        "url": "https://pubmed.ncbi.nlm.nih.gov/27621460/"
      },
      "tags": [
        "l11p3",
        "bombardment",
        "evidence"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "lunar highlands heavily cratered surface Lunar Reconnaissance Orbiter",
        "entityTerm": "Lunar Highlands",
        "imagePrompt": "An orbital photograph of the lunar highlands, the surface saturated with overlapping craters of every size under low sunlight.",
        "alt": "A real telescopic photograph of the Moon at near-full phase, filling the frame against black sky: dark maria (a distinctive isolated oval mare near the right limb, consistent with Mare Crisium)…",
        "depictable": true,
        "credit": "Pexels · Antonio  Moura · Pexels License",
        "creditUrl": "https://www.pexels.com/photo/close-up-shot-of-the-moon-10300049/",
        "subject": "A real telescopic photograph of the Moon at near-full phase, filling the frame against black sky: dark maria (a distinctive isolated oval mare near the right limb, consistent with Mare Crisium) set against the bright, densely cratered highlands, with a bright ray system radiating from a crater at lo",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-late-heavy-bombardment-contested.webp"
      },
      "uid": "13t2s3o10xxupa"
    },
    {
      "id": "ast-f-change6-far-side-test",
      "shape": "fact",
      "title": "The Far Side Answers",
      "body": "Every earlier lunar sample came from the near side. China's **Chang'e-6** returned material from the **South Pole–Aitken basin** on the far side, including impact-melt rock dated to about **4.247 billion years** and basalt around 2.8 billion years old. A 2026 analysis in Science Advances rebuilt the impact flux from them and found **no sign of a spike** at 3.9 billion years — the first independent check from the far side pointed the same way as the Apollo re-analyses.",
      "factVariant": "image-heavy",
      "imageCaption": "Chang'e-6 sampled the South Pole–Aitken basin — the first material returned from the Moon's far side.",
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "South Pole-Aitken basin lunar far side orbital view",
        "entityTerm": "South Pole–Aitken basin",
        "imagePrompt": "An orbital topographic view of the Moon's far side centred on the vast South Pole-Aitken basin, its depth shown against the surrounding highlands.",
        "alt": "NASA Lunar Reconnaissance Orbiter mosaic of the Moon's far side, heavily cratered with almost no dark maria, with a red ellipse drawn over the southern part of the disc outlining the South…",
        "depictable": true,
        "credit": "NASA (the outline of South Pole–Aitken basin is own work) · Public domain",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:South_Pole%E2%80%93Aitken_basin_on_the_Moon%27s_farside.png",
        "subject": "NASA Lunar Reconnaissance Orbiter mosaic of the Moon's far side, heavily cratered with almost no dark maria, with a red ellipse drawn over the southern part of the disc outlining the South Pole–Aitken basin.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-change6-far-side-test.webp"
      },
      "source": {
        "label": "Yue et al. 2026, Science Advances — Lunar chronology model with the Chang'e-6 farside samples",
        "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC12871470/"
      },
      "tags": [
        "l11p3",
        "bombardment",
        "chang-e-6"
      ],
      "uid": "1ycof3wen867o"
    },
    {
      "id": "ast-f-51-pegasi-b-discovery",
      "shape": "fact",
      "title": "The Planet Nobody Expected",
      "body": "In **October 1995** Michel Mayor and Didier Queloz found the first planet orbiting a Sun-like star: **51 Pegasi b**, a gas giant of about 0.46 Jupiter masses circling its star every **4.2 days** at **0.0527 AU** — far closer in than Mercury orbits the Sun. Frost-line reasoning says a giant cannot assemble there, where it is far too hot for ice to survive. It was not an interesting new planet; it was a contradiction. They shared the **2019 Nobel Prize in Physics** for it.",
      "source": {
        "label": "NASA Science — Exoplanet Catalog: 51 Pegasi b",
        "url": "https://science.nasa.gov/exoplanet-catalog/51-pegasi-b/"
      },
      "tags": [
        "l11p3",
        "exoplanets",
        "51-pegasi-b"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Observatoire de Haute-Provence 193 cm telescope dome",
        "entityTerm": "Haute-Provence Observatory",
        "imagePrompt": "A photograph of the Observatoire de Haute-Provence 193 cm telescope inside its dome, the tube and mounting visible.",
        "alt": "The Haute-Provence telescope where the first planet around a Sun-like star was found in 1995",
        "depictable": true,
        "credit": "José Rodrigues · CC BY-SA 4.0",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:T193_in_observations.jpg",
        "subject": "Night interior photo of the T193 telescope, dome slit open to a star-filled sky, control panel and cabling in the foreground — OHP's 1.93 m telescope, clearly titled and well composed.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-51-pegasi-b-discovery.webp"
      },
      "uid": "193h7xc1mmjsgi"
    },
    {
      "id": "ast-f-metre-sized-barrier",
      "shape": "fact",
      "title": "The Step Nobody Can Explain",
      "body": "Nobody has a settled account of how millimetre dust grains got past **metre size**. At around a metre a growing body drifts inward through the disc fast enough to be swallowed by the star before it can grow further — the **metre-sized barrier problem**. The **streaming instability** is described in the literature as a leading candidate, not the answer, and one review lists the growth of the first planetesimals among five unresolved bottlenecks. 'Planets grow by sticking together' is not a complete explanation.",
      "source": {
        "label": "Lim et al. 2024, ApJ — Streaming Instability and Turbulence: Conditions for Planetesimal Formation",
        "url": "https://iopscience.iop.org/article/10.3847/1538-4357/ad47a2"
      },
      "tags": [
        "l11p3",
        "accretion",
        "open-questions"
      ],
      "uid": "1r3lleu1np9xyy"
    },
    {
      "id": "ast-f-frost-line-moves",
      "shape": "fact",
      "title": "The Line That Moves",
      "body": "The frost line is a temperature contour, so it travels. In a typical young disc water stays gaseous out to roughly **3 AU** — about 450 million km — but the boundary shifts as the disc's temperature changes. ALMA caught this directly at the young star **V883 Orionis**, where an outburst of brightness pushed the water snow line out to around **40 AU**, roughly the size of Pluto's orbit. Models show it drifts inward again as a disc's accretion rate falls.",
      "source": {
        "label": "ESO — Stellar Outburst Brings Water Snow Line Into View",
        "url": "https://www.eso.org/public/unitedkingdom/news/eso1626/"
      },
      "tags": [
        "l11p3",
        "frost-line",
        "disc"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "V883 Orionis protoplanetary disc ALMA water snow line",
        "entityTerm": "V883 Orionis",
        "imagePrompt": "An ALMA image of the V883 Orionis disc as a bright ringed structure, with the water snow line marked at a radius well outside the star.",
        "alt": "ALMA false-colour orange millimetre image of the protoplanetary disc around the young star V883 Orionis (ESO press image eso1626b), a tilted disc on black with a bright central core and a darker…",
        "depictable": true,
        "credit": "Wikimedia Commons · ALMA (ESO/NAOJ/NRAO)/L. Cieza · CC BY 4.0",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:ALMA_image_of_the_protoplanetary_disc_around_V883_Orionis_(eso1626b).jpg",
        "subject": "ALMA false-colour orange millimetre image of the protoplanetary disc around the young star V883 Orionis (ESO press image eso1626b), a tilted disc on black with a bright central core and a darker ring around it marking the water snow line pushed out to about 40 AU.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-frost-line-moves.webp"
      },
      "uid": "1hdttlm32j9dm"
    },
    {
      "id": "ast-d-hot-jupiter",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Hot Jupiter"
      },
      "definition": {
        "modality": "text",
        "value": "A gas giant that circles its star in days rather than years, roasting closer in than Mercury sits to the Sun — a class with no counterpart in our own system"
      },
      "source": {
        "label": "NASA Science — Exoplanets",
        "url": "https://science.nasa.gov/exoplanets/"
      },
      "tags": [
        "l11p3",
        "exoplanets",
        "migration"
      ],
      "uid": "dqzcuw1b1vp3m"
    },
    {
      "id": "ast-p-returned-moon-rock",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "All the Moon rock we hold"
      },
      "sideB": {
        "modality": "text",
        "value": "About 385 kg, from Apollo, Luna and both Chang'e missions"
      },
      "source": {
        "label": "Li et al. 2024, National Science Review — Chang'E-6 lunar far-side samples",
        "url": "https://pmc.ncbi.nlm.nih.gov/articles/PMC11495410/"
      },
      "tags": [
        "l11p3",
        "samples",
        "evidence"
      ],
      "uid": "18pjlsh1cgr653"
    },
    {
      "id": "ast-q-late-heavy-bombardment-status",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "What is the current standing of the proposed 3.9-billion-year impact spike?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Contested, then confirmed"
        },
        {
          "modality": "text",
          "value": "Contested only on timing"
        },
        {
          "modality": "text",
          "value": "Seriously contested"
        },
        {
          "modality": "text",
          "value": "Never proposed at all"
        }
      ],
      "correctIndex": 2,
      "explanation": "It was proposed and is now seriously questioned — Chang'e-6's far-side samples were returned to test whether the spike is real or an artefact of where Apollo landed. It was certainly proposed, has not been confirmed, and the doubt is about whether the spike happened at all, not just when.",
      "source": {
        "label": "Boehnke & Harrison 2016, PNAS — Illusory Late Heavy Bombardments",
        "url": "https://pubmed.ncbi.nlm.nih.gov/27621460/"
      },
      "tags": [
        "l11p3",
        "bombardment",
        "evidence"
      ],
      "uid": "1gtl0vc17wbpvi"
    },
    {
      "id": "ast-q-exoplanets-not-default",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "What did three decades of exoplanet hunting show about our own layout?"
      },
      "options": [
        {
          "modality": "text",
          "value": "One outcome among many"
        },
        {
          "modality": "text",
          "value": "The only one of its kind so far"
        },
        {
          "modality": "text",
          "value": "Still too early to say"
        },
        {
          "modality": "text",
          "value": "The commonest we have found"
        }
      ],
      "correctIndex": 0,
      "explanation": "More than 6,000 confirmed planets show arrangements with no counterpart here — hot Jupiters roasting days from their stars. Ours is one arrangement among many, and not the commonest. Nor is it unique: surveys reach only a thin, biased slice of the galaxy.",
      "source": {
        "label": "NASA Science — Exoplanets",
        "url": "https://science.nasa.gov/exoplanets/"
      },
      "tags": [
        "l11p3",
        "exoplanets",
        "migration"
      ],
      "uid": "k5dgkk51v5q"
    },
    {
      "id": "czr-ast-d-hot-jupiter",
      "shape": "cloze",
      "derivedFrom": "ast-d-hot-jupiter",
      "template": "___ — A gas giant that circles its star in days rather than years, roasting closer in than Mercury sits to the Sun — a class with no counterpart in our own system",
      "answer": "Hot Jupiter",
      "distractors": [
        "Fireball",
        "Ice giant",
        "Rock comet"
      ],
      "explanation": "Hot Jupiter is a gas giant that circles its star in days rather than years, roasting closer in than Mercury sits to the Sun. Fireball, the closest of the alternatives, is a meteor brighter than magnitude −4, about as bright as Venus at its best.",
      "source": {
        "label": "NASA Science — Exoplanets",
        "url": "https://science.nasa.gov/exoplanets/"
      },
      "tags": [
        "l11p3",
        "exoplanets",
        "migration",
        "derived"
      ],
      "uid": "1dychph1swk6k9"
    },
    {
      "id": "tfr-ast-d-hot-jupiter",
      "shape": "trueFalse",
      "derivedFrom": "ast-d-hot-jupiter",
      "statement": "Hot Jupiter — a gas giant that circles its star in days rather than years, roasting closer in than Mercury sits to the Sun.",
      "isTrue": true,
      "why": "A hot Jupiter is a gas giant that circles its star in days rather than years, roasting closer in than Mercury sits to the Sun — the first kind of exoplanet found around a Sun-like star. A rock comet is far smaller: an asteroid that sheds dust in the Sun's heat.",
      "source": {
        "label": "NASA Science — Exoplanets",
        "url": "https://science.nasa.gov/exoplanets/"
      },
      "tags": [
        "l11p3",
        "exoplanets",
        "migration",
        "derived"
      ],
      "uid": "11drtux1k3myw5"
    },
    {
      "id": "ast-f-molecular-cloud-cold",
      "shape": "fact",
      "title": "The Coldest Nurseries",
      "body": "Stars condense out of **molecular clouds** — the coldest and densest parts of the interstellar medium, at only **10 to 20 kelvin**, roughly −263 to −253 °C. A single cloud holds between **1,000 and 10 million** times the mass of the Sun. Star formation does not begin with something hot. It begins with gas cold enough that its own pressure cannot resist gravity.",
      "factVariant": "image-heavy",
      "imageCaption": "Star birth starts colder than anything on Earth, not hotter.",
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "dark molecular cloud silhouetted against background starlight",
        "entityTerm": "Molecular cloud",
        "imagePrompt": "A photograph of a dark, dusty molecular cloud silhouetted as an opaque black shape against a bright, crowded background star field.",
        "alt": "Hubble's \"Fairy of Eagle Nebula\" — a tall dark pillar of dense, cold gas and dust in the Eagle Nebula (M16), silhouetted against glowing orange-and-blue nebulosity with scattered stars around it;",
        "depictable": true,
        "credit": "NASA, ESA, and The Hubble Heritage Team (STScI/AURA) · Public domain",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:Fairy_of_Eagle_Nebula.jpg",
        "subject": "Hubble's \"Fairy of Eagle Nebula\" — a tall dark pillar of dense, cold gas and dust in the Eagle Nebula (M16), silhouetted against glowing orange-and-blue nebulosity with scattered stars around it; a star-forming molecular cloud column being eroded by nearby hot stars.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-molecular-cloud-cold.webp"
      },
      "source": {
        "label": "Chandra X-ray Center — Giant Molecular Clouds and Protostars",
        "url": "https://chandra.harvard.edu/edu/formal/stellar_ev/story/index2.html"
      },
      "tags": [
        "l12p1",
        "star-formation",
        "molecular-clouds"
      ],
      "uid": "y8r6gj9qsajd"
    },
    {
      "id": "ast-f-protostar-glows-first",
      "shape": "fact",
      "title": "Gravity Lights It First",
      "body": "Gravity pulls the densest clumps of a cloud inward, and the infalling material **heats as it is compressed**. The hot contracting ball at the centre is a **protostar** — already at **2,000 to 3,000 K** with no fusion at all — hot enough to glow red, though the dust cocoon around it blocks that light, so protostars are found in the infrared rather than by eye. Birth is not gentle: only about **10 percent** of protostars survive their birth region, the rest disrupted by nearby radiation and outflows. Gravity does the heating first; nuclear physics takes over later.",
      "source": {
        "label": "Chandra X-ray Center — Giant Molecular Clouds and Protostars",
        "url": "https://chandra.harvard.edu/edu/formal/stellar_ev/story/index2.html"
      },
      "tags": [
        "l12p1",
        "star-formation",
        "protostar"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Herbig-Haro object HH 211 protostellar jet Webb infrared image",
        "entityTerm": "Herbig–Haro object",
        "imagePrompt": "A Webb infrared image of a bipolar protostellar jet: twin knotted orange outflows streaming in opposite directions from a dark obscured centre.",
        "alt": "The JWST NIRCam infrared image of Herbig-Haro 211 (HH 211): a bipolar protostellar jet with two pink-red lobes of shocked gas and bow shocks running diagonally out from a dark, dust-obscured…",
        "depictable": true,
        "credit": "ESA/Webb, NASA, CSA, T. Ray (Dublin Institute for Advanced Studies) (Openverse) · by 4.0",
        "creditUrl": "https://commons.wikimedia.org/w/index.php?curid=137627717",
        "subject": "The JWST NIRCam infrared image of Herbig-Haro 211 (HH 211): a bipolar protostellar jet with two pink-red lobes of shocked gas and bow shocks running diagonally out from a dark, dust-obscured centre where the protostar is hidden, with diffraction-spiked stars in the background.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-protostar-glows-first.webp"
      },
      "uid": "n9hr9pgtmtxv"
    },
    {
      "id": "ast-f-fusion-ignition-point",
      "shape": "fact",
      "title": "Fifteen Million Degrees",
      "body": "A protostar becomes a **star** at a definable moment: when its core reaches about **15 million degrees** and **hydrogen fusion** begins. That is an operational definition, not a vague label. Before ignition there is a contracting ball of gas that happens to glow. After it, there is an engine.",
      "source": {
        "label": "NASA Imagine the Universe — Background: Life Cycles of Stars",
        "url": "https://imagine.gsfc.nasa.gov/educators/lessons/xray_spectra/background-lifecycles.html"
      },
      "tags": [
        "l12p1",
        "star-formation",
        "fusion"
      ],
      "uid": "1wsnuea1qtah7m"
    },
    {
      "id": "ast-f-cno-twentieth-power",
      "shape": "fact",
      "title": "Temperature to the Twentieth",
      "body": "How a star fuses depends on how hot its core is. The **proton-proton chain** dominates in stars like the Sun, and its rate climbs only as temperature to the **4th power**. The **CNO cycle** rate climbs as roughly temperature to the **20th power**, so it takes over above about **1.1 solar masses**. A modest temperature rise barely moves one reaction and transforms the other — which is why a heavier star does not simply have more fuel, it also burns a far more temperature-hungry one.",
      "source": {
        "label": "Case Western Reserve University — Nuclear Reactions in Stars",
        "url": "https://burro.case.edu/Academics/Astr221/StarPhys/nuclear2.html"
      },
      "tags": [
        "l12p1",
        "fusion",
        "cno-cycle"
      ],
      "uid": "bnulnhqphjzn"
    },
    {
      "id": "ast-p-giant-molecular-cloud",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Giant molecular cloud"
      },
      "sideB": {
        "modality": "text",
        "value": "Any such body above about 100,000 solar masses",
        "short": "Above 100,000 solar masses"
      },
      "source": {
        "label": "Chandra X-ray Center — Giant Molecular Clouds and Protostars",
        "url": "https://chandra.harvard.edu/edu/formal/stellar_ev/story/index2.html"
      },
      "tags": [
        "l12p1",
        "molecular-clouds",
        "vocabulary"
      ],
      "uid": "181hgkf10i4dnr"
    },
    {
      "id": "ast-p-protostar-survival",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Protostar survival"
      },
      "sideB": {
        "modality": "text",
        "value": "About 1 in 10 gets out of the birth region — one widely cited estimate",
        "short": "About 1 in 10, on one estimate"
      },
      "source": {
        "label": "Chandra X-ray Center — Giant Molecular Clouds and Protostars",
        "url": "https://chandra.harvard.edu/edu/formal/stellar_ev/story/index2.html"
      },
      "tags": [
        "l12p1",
        "star-formation",
        "protostar"
      ],
      "uid": "83hu9l1joh3ar"
    },
    {
      "id": "ast-d-protostar",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Protostar"
      },
      "definition": {
        "modality": "text",
        "value": "A contracting ball of infalling gas that already glows from compression alone, before any fusion has started in its core"
      },
      "curatedDistractors": [
        "Molecular cloud",
        "Main-sequence star",
        "Interstellar medium"
      ],
      "source": {
        "label": "NASA Science — Stars",
        "url": "https://science.nasa.gov/universe/stars/"
      },
      "tags": [
        "l12p1",
        "star-formation",
        "vocabulary"
      ],
      "uid": "1sg93u6tz5j40"
    },
    {
      "id": "ast-q-starbirth-gas-temperature",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "What temperature is the gas that star formation starts in?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Around 300 kelvin"
        },
        {
          "modality": "text",
          "value": "2,000 to 3,000 kelvin"
        },
        {
          "modality": "text",
          "value": "About 15 million kelvin"
        },
        {
          "modality": "text",
          "value": "10 to 20 kelvin"
        }
      ],
      "correctIndex": 3,
      "explanation": "Molecular clouds are the coldest, densest part of the interstellar medium. 2,000 to 3,000 K is the protostar once it is already contracting, and 15 million is the core at ignition — both come later. 300 K is about room temperature, far too warm for gravity to win.",
      "source": {
        "label": "Chandra X-ray Center — Giant Molecular Clouds and Protostars",
        "url": "https://chandra.harvard.edu/edu/formal/stellar_ev/story/index2.html"
      },
      "tags": [
        "l12p1",
        "molecular-clouds",
        "temperature"
      ],
      "uid": "6xdrk3skkbnf"
    },
    {
      "id": "ast-q-protostar-glow-cause",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Why does a protostar already shine before it is a star?"
      },
      "options": [
        {
          "modality": "text",
          "value": "It reflects nearby starlight"
        },
        {
          "modality": "text",
          "value": "Hydrogen fusion has begun"
        },
        {
          "modality": "text",
          "value": "Its cloud was warm to start"
        },
        {
          "modality": "text",
          "value": "Compression heats the gas"
        }
      ],
      "correctIndex": 3,
      "explanation": "Infalling material heats as it is squeezed — gravity does the work before nuclear physics does. Fusion has not begun; that waits for 15 million degrees. Reflection could never reach 2,000 to 3,000 K. And the cloud it forms in is 10 to 20 kelvin, the coldest gas around.",
      "source": {
        "label": "NASA Science — Stars",
        "url": "https://science.nasa.gov/universe/stars/"
      },
      "tags": [
        "l12p1",
        "protostar",
        "quiz"
      ],
      "uid": "1e9lcto1366uu"
    },
    {
      "id": "ast-q-cno-temperature-exponent",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "How steeply does the CNO cycle's rate climb with core temperature?"
      },
      "options": [
        {
          "modality": "text",
          "value": "As the 8th power"
        },
        {
          "modality": "text",
          "value": "As the 20th power"
        },
        {
          "modality": "text",
          "value": "As the 4th power"
        },
        {
          "modality": "text",
          "value": "In direct proportion"
        }
      ],
      "correctIndex": 1,
      "explanation": "The 4th power is the proton-proton chain's dependence, not this one's. Direct proportion and an 8th-power climb both badly understate it: the gap between 4 and 20 is exactly why a modest temperature rise barely moves one reaction and transforms the other.",
      "source": {
        "label": "Case Western Reserve University — Nuclear Reactions in Stars",
        "url": "https://burro.case.edu/Academics/Astr221/StarPhys/nuclear2.html"
      },
      "tags": [
        "l12p1",
        "cno-cycle",
        "quiz"
      ],
      "uid": "dnqq90izf7yc"
    },
    {
      "id": "czr-ast-d-protostar",
      "shape": "cloze",
      "derivedFrom": "ast-d-protostar",
      "template": "___ — A contracting ball of infalling gas that already glows from compression alone, before any fusion has started in its core",
      "answer": "Protostar",
      "distractors": [
        "Fireball",
        "Ice giant",
        "Rock comet"
      ],
      "explanation": "Protostar is a contracting ball of infalling gas that already glows from compression alone, before any fusion has started in its core. Fireball, the closest of the alternatives, is a meteor brighter than magnitude −4, about as bright as Venus at its best.",
      "source": {
        "label": "NASA Science — Stars",
        "url": "https://science.nasa.gov/universe/stars/"
      },
      "tags": [
        "l12p1",
        "star-formation",
        "vocabulary",
        "derived"
      ],
      "uid": "1rdnncrryvq0n"
    },
    {
      "id": "ast-f-spectral-colour-thermometer",
      "shape": "fact",
      "title": "Colour Is a Thermometer",
      "body": "Sort stars by surface temperature and they fall into a sequence: **O, B, A, F, G, K, M**. O-class stars run **28,000–50,000 K** and burn blue. **G-class**, the Sun's class, sits at **4,900–6,000 K** and looks yellow. M-class bottoms out around **2,000 K** and glows red. Taps and warning lights have trained you backwards: in stars, blue is the hot end and red is the cool one.",
      "factVariant": "image-heavy",
      "imageCaption": "Blue is the hot end of the sequence. Red is the cool one.",
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "OBAFGKM spectral class temperature and colour sequence chart",
        "imagePrompt": "Flat vector horizontal chart of the OBAFGKM classes in order, each band coloured from blue-white through white and yellow to orange-red, labelled with its temperature range and the Sun marked in G.",
        "alt": "Chart of the O to M spectral sequence running from blue at 50,000 K down to red at 2,000 K, with the Sun's G class marked",
        "depictable": true,
        "allowGenerated": true
      },
      "source": {
        "label": "CSIRO Australia Telescope National Facility — Spectral Classification",
        "url": "https://www.atnf.csiro.au/outreach/education/senior/astrophysics/spectral_class.html"
      },
      "tags": [
        "l12p2",
        "spectral-class",
        "temperature"
      ],
      "uid": "5bg3ew1qog8qw"
    },
    {
      "id": "ast-f-obafgkm-history",
      "shape": "fact",
      "title": "A Fossil of Its History",
      "body": "The letters are out of alphabetical order for an entirely human reason. **Edward Pickering** first ranked stars A, B, C by the strength of their hydrogen lines. **Annie Jump Cannon** later realised the same stars could be sorted by temperature instead, reordered the surviving classes, and kept the old labels. OBAFGKM is not a random jumble, and the letters stand for nothing — the sequence is a fossil of its own history.",
      "source": {
        "label": "Chandra X-ray Center — What do the initials of OBAFGKM mean?",
        "url": "https://chandra.harvard.edu/resources/faq/astrophysics/astrophysics-56.html"
      },
      "tags": [
        "l12p2",
        "spectral-class",
        "history"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Annie Jump Cannon at the Harvard College Observatory photograph",
        "entityTerm": "Annie Jump Cannon",
        "subjectType": "person",
        "profile": "archive-first",
        "imagePrompt": "A historical photograph of Annie Jump Cannon seated at a desk at the Harvard College Observatory examining photographic spectral plates.",
        "alt": "Black-and-white Smithsonian Institution Archives photograph of Annie Jump Cannon seated at her desk in her office at the Harvard College Observatory, with a glass plate-viewing frame on the desk…",
        "depictable": true,
        "credit": "Smithsonian Institution from United States · No restrictions",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:Annie_Jump_Cannon_sitting_at_desk.jpg",
        "subject": "Black-and-white Smithsonian Institution Archives photograph of Annie Jump Cannon seated at her desk in her office at the Harvard College Observatory, with a glass plate-viewing frame on the desk and plate-storage cabinets and bookshelves behind her.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-obafgkm-history.webp"
      },
      "uid": "n1szhv2hdzmx"
    },
    {
      "id": "ast-f-mass-luminosity-power",
      "shape": "fact",
      "title": "Sixteen Times the Light",
      "body": "On the main sequence, luminosity scales roughly as mass to the power **3.5 to 4** — so doubling a star's mass makes it something like **eleven to sixteen times** brighter, not twice as bright. Reputable sources give both exponents, so this is a rule of thumb rather than a law. Brightness is not proportional to mass; it is a steep power of it.",
      "source": {
        "label": "Penn State ASTRO 801 — The Mass-Luminosity Relationship",
        "url": "https://courses.ems.psu.edu/astro801/content/l7_p3.html"
      },
      "tags": [
        "l12p2",
        "mass-luminosity",
        "main-sequence"
      ],
      "uid": "1smzfwk1481zhi"
    },
    {
      "id": "ast-f-massive-stars-die-young",
      "shape": "fact",
      "title": "Live Fast, Die Young",
      "body": "Because luminosity rises far faster than mass, a heavier star spends its fuel disproportionately fast: main sequence lifetime falls as roughly mass to the power **−2.5 to −3** — sources give both. A star ten times the Sun’s mass lasts somewhere between **316 and 1,000 times** less long, not ten times. Ten solar masses buys roughly **10 million years**; the Sun gets about **10 billion**; a 0.1-solar-mass red dwarf, on the order of **10 trillion**. Six orders of magnitude of lifetime out of two orders of magnitude of mass.",
      "source": {
        "label": "Penn State ASTRO 801 — The Mass-Luminosity Relationship",
        "url": "https://courses.ems.psu.edu/astro801/content/l7_p3.html"
      },
      "tags": [
        "l12p2",
        "main-sequence",
        "lifetime"
      ],
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "main sequence lifetime versus stellar mass chart",
        "imagePrompt": "Flat vector log-log chart of main sequence lifetime against stellar mass, a steep downward line marked at 0.1, 1 and 10 solar masses with their lifetimes labelled.",
        "alt": "Log chart of main sequence lifetime against mass: ten solar masses buys ten million years, one solar mass buys ten billion",
        "depictable": true,
        "allowGenerated": true
      },
      "uid": "1056f4qwze8bq"
    },
    {
      "id": "ast-f-sunlike-quiet-ending",
      "shape": "fact",
      "title": "The Quiet Ending",
      "body": "A red giant sheds its outer layers as a **planetary nebula**, which glows for only about **20,000 years** before dispersing — a flicker, which is why so few exist at any moment. The name is an eighteenth-century telescope error; these have nothing whatever to do with planets. What is left is the exposed core: a **white dwarf**, roughly Earth-sized, about a **billion kilograms per cubic metre**, with no fusion at all, cooling for tens to hundreds of billions of years.",
      "source": {
        "label": "ESA/Hubble — Planetary Nebula",
        "url": "https://esahubble.org/wordbank/planetary-nebula/"
      },
      "tags": [
        "l12p2",
        "planetary-nebula",
        "white-dwarf"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Ring Nebula planetary nebula Hubble image",
        "entityTerm": "Ring Nebula",
        "imagePrompt": "A Hubble-style image of a planetary nebula as a coloured ring or shell of ionised gas with the hot white dwarf remnant at its centre.",
        "alt": "The Ring Nebula (M57), a planetary nebula, as imaged by JWST's NIRCam: an elliptical ring of orange-pink and white filamentary gas around a teal-blue interior, with the faint central white dwarf…",
        "depictable": true,
        "credit": "Wikipedia — Ring Nebula · See Wikimedia Commons",
        "creditUrl": "https://en.wikipedia.org/wiki/Ring_Nebula",
        "subject": "The Ring Nebula (M57), a planetary nebula, as imaged by JWST's NIRCam: an elliptical ring of orange-pink and white filamentary gas around a teal-blue interior, with the faint central white dwarf visible at the middle, set against a black star field with JWST diffraction-spiked stars.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-sunlike-quiet-ending.webp"
      },
      "uid": "1end4qak9rvn0"
    },
    {
      "id": "ast-p-red-dwarf-share",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Red dwarfs"
      },
      "sideB": {
        "modality": "text",
        "value": "About 75 percent of the Milky Way's stars"
      },
      "source": {
        "label": "NASA Science — Star Types",
        "url": "https://science.nasa.gov/universe/stars/types/"
      },
      "tags": [
        "l12p2",
        "red-dwarf",
        "population"
      ],
      "uid": "1twq35w10ts99m"
    },
    {
      "id": "ast-p-hr-diagram-axes",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Hertzsprung-Russell diagram"
      },
      "sideB": {
        "modality": "text",
        "value": "Surface temperature plotted against luminosity",
        "short": "Temperature against luminosity"
      },
      "source": {
        "label": "ESO — Hertzsprung-Russell Diagram",
        "url": "https://www.eso.org/public/images/eso0728c/"
      },
      "tags": [
        "l12p2",
        "hr-diagram",
        "vocabulary"
      ],
      "uid": "l20ql7109510b"
    },
    {
      "id": "ast-d-main-sequence",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Main sequence"
      },
      "definition": {
        "modality": "text",
        "value": "The diagonal band of stars still fusing hydrogen in the core — the long stable middle of a star's life rather than a type of star, which is why around 90 percent are caught in it"
      },
      "curatedDistractors": [
        "Hertzsprung-Russell diagram",
        "Spectral class",
        "Red giant branch"
      ],
      "source": {
        "label": "NASA Science — Star Types",
        "url": "https://science.nasa.gov/universe/stars/types/"
      },
      "tags": [
        "l12p2",
        "main-sequence",
        "vocabulary"
      ],
      "uid": "7kx1sormusrm"
    },
    {
      "id": "ast-q-tenfold-mass-lifetime",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "How does a 10-solar-mass star's time on the main sequence compare with the Sun's?"
      },
      "options": [
        {
          "modality": "text",
          "value": "About ten times shorter"
        },
        {
          "modality": "text",
          "value": "About three times shorter"
        },
        {
          "modality": "text",
          "value": "Hundreds to a thousand times"
        },
        {
          "modality": "text",
          "value": "Very slightly shorter"
        }
      ],
      "correctIndex": 2,
      "explanation": "Lifetime falls as mass to roughly the power -2.5 to -3, so ten times the mass buys between about 316 and 1,000 times less time: ~10 million years against the Sun's ~10 billion. Ten times and three times both assume lifetime tracks mass directly, which is the mistake.",
      "source": {
        "label": "Penn State ASTRO 801 — The Mass-Luminosity Relationship",
        "url": "https://courses.ems.psu.edu/astro801/content/l7_p3.html"
      },
      "tags": [
        "l12p2",
        "lifetime",
        "quiz"
      ],
      "uid": "1d1zsu31p6xjp3"
    },
    {
      "id": "ast-q-core-collapse-birth-mass",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "How heavy must a star be at birth to end in core collapse?"
      },
      "options": [
        {
          "modality": "text",
          "value": "About 8 solar masses"
        },
        {
          "modality": "text",
          "value": "About 2 solar masses"
        },
        {
          "modality": "text",
          "value": "About 25 solar masses"
        },
        {
          "modality": "text",
          "value": "About 80 solar masses"
        }
      ],
      "correctIndex": 0,
      "explanation": "Below roughly that figure a star ends quietly instead. It is a teaching approximation, not a line: modelling puts the minimum near 8.3 at low metal content, rising to about 9.5 at solar metallicity. The 2, 25 and 80 options all sit far from where the transition happens.",
      "source": {
        "label": "CSIRO ATNF — The Death of Stars I: Solar-Mass Stars",
        "url": "https://www.atnf.csiro.au/resources/education/senior-astrophysics/stellarevolution/deathlow/"
      },
      "tags": [
        "l12p2",
        "core-collapse",
        "quiz"
      ],
      "uid": "1mx1n8zqg9kb"
    },
    {
      "id": "ast-n-oclass-hot-end",
      "shape": "numeric",
      "prompt": {
        "modality": "text",
        "value": "Blue O-class stars, at their hottest"
      },
      "value": 50000,
      "unit": "K",
      "tolerance": 2000,
      "source": {
        "label": "CSIRO Australia Telescope National Facility — Spectral Classification",
        "url": "https://www.atnf.csiro.au/outreach/education/senior/astrophysics/spectral_class.html"
      },
      "tags": [
        "l12p2",
        "spectral-class",
        "temperature"
      ],
      "uid": "18u2mqr1dhd7pb"
    },
    {
      "id": "ast-n-oclass-cool-end",
      "shape": "numeric",
      "prompt": {
        "modality": "text",
        "value": "Blue O-class stars, at their coolest"
      },
      "value": 28000,
      "unit": "K",
      "tolerance": 1500,
      "source": {
        "label": "CSIRO Australia Telescope National Facility — Spectral Classification",
        "url": "https://www.atnf.csiro.au/outreach/education/senior/astrophysics/spectral_class.html"
      },
      "tags": [
        "l12p2",
        "spectral-class",
        "temperature"
      ],
      "uid": "zzvnmun6kj64"
    },
    {
      "id": "ast-n-gclass-hot-end",
      "shape": "numeric",
      "prompt": {
        "modality": "text",
        "value": "Yellow G-class stars, at their hottest"
      },
      "value": 6000,
      "unit": "K",
      "tolerance": 200,
      "source": {
        "label": "CSIRO Australia Telescope National Facility — Spectral Classification",
        "url": "https://www.atnf.csiro.au/outreach/education/senior/astrophysics/spectral_class.html"
      },
      "tags": [
        "l12p2",
        "spectral-class",
        "temperature"
      ],
      "uid": "183w20o9onyjc"
    },
    {
      "id": "ast-n-gclass-cool-end",
      "shape": "numeric",
      "prompt": {
        "modality": "text",
        "value": "Yellow G-class stars, at their coolest"
      },
      "value": 4900,
      "unit": "K",
      "tolerance": 200,
      "source": {
        "label": "CSIRO Australia Telescope National Facility — Spectral Classification",
        "url": "https://www.atnf.csiro.au/outreach/education/senior/astrophysics/spectral_class.html"
      },
      "tags": [
        "l12p2",
        "spectral-class",
        "temperature"
      ],
      "uid": "l7ys0t1l7yniz"
    },
    {
      "id": "ast-n-mclass-hot-end",
      "shape": "numeric",
      "prompt": {
        "modality": "text",
        "value": "Red M-class stars, at their hottest"
      },
      "value": 3500,
      "unit": "K",
      "tolerance": 150,
      "source": {
        "label": "CSIRO Australia Telescope National Facility — Spectral Classification",
        "url": "https://www.atnf.csiro.au/outreach/education/senior/astrophysics/spectral_class.html"
      },
      "tags": [
        "l12p2",
        "spectral-class",
        "temperature"
      ],
      "uid": "t4xlytlew5o9"
    },
    {
      "id": "ast-n-mclass-cool-end",
      "shape": "numeric",
      "prompt": {
        "modality": "text",
        "value": "Red M-class stars, at their coolest"
      },
      "value": 2000,
      "unit": "K",
      "tolerance": 150,
      "source": {
        "label": "CSIRO Australia Telescope National Facility — Spectral Classification",
        "url": "https://www.atnf.csiro.au/outreach/education/senior/astrophysics/spectral_class.html"
      },
      "tags": [
        "l12p2",
        "spectral-class",
        "temperature"
      ],
      "uid": "12s2bmr1kfxmon"
    },
    {
      "id": "tfr-ast-d-main-sequence",
      "shape": "trueFalse",
      "derivedFrom": "ast-d-main-sequence",
      "statement": "Main sequence — the outer part of a shadow, where the light source is partly blocked rather than hidden completely.",
      "isTrue": false,
      "why": "The main sequence is the diagonal band of stars still fusing hydrogen in the core, where a star spends most of its life. A penumbra is a shadow term rather than a stellar one: the outer part of a shadow, where the light source is partly blocked rather than hidden completely.",
      "source": {
        "label": "NASA Science — Star Types",
        "url": "https://science.nasa.gov/universe/stars/types/"
      },
      "tags": [
        "l12p2",
        "main-sequence",
        "vocabulary",
        "derived"
      ],
      "whyOptions": [
        "Coronal hole",
        "Exosphere",
        "Penumbra"
      ],
      "whyCorrectIndex": 2,
      "uid": "1t1w5dy1ympfvu"
    },
    {
      "id": "ast-f-supernova-light-is-leftover",
      "shape": "fact",
      "title": "The Light Is Leftover",
      "body": "A **core-collapse supernova** releases about **10^46 joules** in a matter of seconds — some 50 times more than the Sun will put out in 10 billion years. About **99 percent** of that leaves as **neutrinos**, in a burst roughly ten seconds long; twenty-five of them were caught on Earth from SN 1987A. The blinding light is the remaining one percent. It is the leftover, not the explosion.",
      "factVariant": "image-heavy",
      "imageCaption": "The part you can see is about one percent of the event.",
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "supernova remnant expanding shell of filaments",
        "entityTerm": "Supernova remnant",
        "imagePrompt": "A photograph of a supernova remnant as a delicate expanding shell of coloured filaments and wisps against a starry background.",
        "alt": "A supernova remnant's expanding shell of filaments — the visible one per cent, after the neutrinos have long gone",
        "depictable": true,
        "credit": "Wikipedia — Veil Nebula · See Wikimedia Commons",
        "creditUrl": "https://en.wikipedia.org/wiki/Veil_Nebula",
        "subject": "The Veil Nebula: delicate glowing red, blue and cyan wisps of gas forming a curved ribbon of an expanding supernova-remnant shell, no text, clean composition.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-supernova-light-is-leftover.webp"
      },
      "source": {
        "label": "Fermilab — All Things Neutrino: Supernova Neutrinos",
        "url": "https://neutrinos.fnal.gov/sources/supernova-neutrinos/"
      },
      "tags": [
        "l12p3",
        "supernova",
        "neutrinos"
      ],
      "uid": "ylgis81bjoy4g"
    },
    {
      "id": "ast-f-iron-stops-paying",
      "shape": "fact",
      "title": "Where Fusion Stops Paying",
      "body": "A massive star builds heavier elements in shells until it makes **iron**, and there the engine stops: because of iron's nuclear structure, fusing it yields **no net energy**. Around **10 billion K** the iron itself comes apart, the support under the star's outer layers vanishes, and the core falls inward at **tens of thousands of kilometres per second**. The star does not explode because it ran out of fuel. It explodes because its remaining fuel would cost energy to burn.",
      "source": {
        "label": "CSIRO ATNF — The Death of Stars II: High-Mass Stars",
        "url": "https://www.atnf.csiro.au/resources/education/senior-astrophysics/stellarevolution/deathhigh/"
      },
      "tags": [
        "l12p3",
        "supernova",
        "iron"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Cassiopeia A supernova remnant Chandra X-ray element map",
        "entityTerm": "Cassiopeia A",
        "imagePrompt": "A Chandra X-ray image of the Cassiopeia A supernova remnant, an expanding shell colour-mapped by elemental emission with the compact remnant at its centre.",
        "alt": "Cassiopeia A in X-rays, its debris colour-coded by element — the shells a massive star built before iron stopped paying",
        "depictable": true,
        "credit": "Wikipedia — Cassiopeia A · See Wikimedia Commons",
        "creditUrl": "https://en.wikipedia.org/wiki/Cassiopeia_A",
        "subject": "A vivid red/white/blue Chandra-based composite of Cassiopeia A: the full circular, filamentary supernova-remnant shell against a dense starfield. Wikipedia's own lead image for the 'Cassiopeia A' article — correct subject, clean composition.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-iron-stops-paying.webp"
      },
      "uid": "11ssklx1yiowh1"
    },
    {
      "id": "ast-f-three-remnant-endings",
      "shape": "fact",
      "title": "Three Endings, One Number",
      "body": "What a collapsed core becomes depends on a single number — its own mass. Below about **1.4 solar masses** it is a **white dwarf**. Between roughly **1.4 and 3**, a **neutron star**. Above that, a **black hole**. Not every star can take the last route: NASA notes the Sun would need to be about **20 times more massive** to end its life as one. Mass decides, and the Sun does not qualify however long it lives.",
      "source": {
        "label": "NASA Imagine the Universe — Background: Life Cycles of Stars",
        "url": "https://imagine.gsfc.nasa.gov/educators/lessons/xray_spectra/background-lifecycles.html"
      },
      "tags": [
        "l12p3",
        "remnants",
        "classification"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Crab Nebula pulsar Hubble image",
        "entityTerm": "Crab Nebula",
        "imagePrompt": "A Hubble-style image of the Crab Nebula: a tangled cage of orange filaments around a blue synchrotron interior with the pulsar at its heart.",
        "alt": "The Crab Nebula (M1), the famous Hubble Space Telescope mosaic: a tangle of orange-red and green filaments surrounding a hazy blue synchrotron glow, with the pulsar among the stars at the centre…",
        "depictable": true,
        "credit": "Wikipedia — Crab Nebula · See Wikimedia Commons",
        "creditUrl": "https://en.wikipedia.org/wiki/Crab_Nebula",
        "subject": "The Crab Nebula (M1), the famous Hubble Space Telescope mosaic: a tangle of orange-red and green filaments surrounding a hazy blue synchrotron glow, with the pulsar among the stars at the centre, against a black starfield.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-three-remnant-endings.webp"
      },
      "uid": "sedmw72rea05"
    },
    {
      "id": "ast-f-remnant-limits-approximate",
      "shape": "fact",
      "title": "Not Constants of Nature",
      "body": "Those thresholds are approximate, and the honest version says so. CSIRO notes the **neutron-star upper limit is not well defined** and may reach **5 solar masses** in some models. NASA puts core-collapse progenitors at roughly **8 to 20 solar masses** for a neutron star, with **heavier stars still** collapsing to a black hole — and the boundary between the two outcomes is a modelling question, not a measured line.",
      "source": {
        "label": "CSIRO ATNF — The Death of Stars II: High-Mass Stars",
        "url": "https://www.atnf.csiro.au/resources/education/senior-astrophysics/stellarevolution/deathhigh/"
      },
      "tags": [
        "l12p3",
        "remnants",
        "uncertainty"
      ],
      "uid": "cjt3yf15k5qe5"
    },
    {
      "id": "ast-p-tov-limit",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Tolman-Oppenheimer-Volkoff limit"
      },
      "sideB": {
        "modality": "text",
        "value": "Roughly 2.0 to 2.2 solar masses, and still being pinned down",
        "short": "Roughly 2.0 to 2.2 solar masses"
      },
      "source": {
        "label": "Rezzolla, Most & Weih 2018 — Constraining the maximum mass of neutron stars (ApJL 852, L25)",
        "url": "https://arxiv.org/abs/1711.00314"
      },
      "tags": [
        "l12p3",
        "neutron-star",
        "uncertainty"
      ],
      "uid": "1h4uk938aprix"
    },
    {
      "id": "ast-d-chandrasekhar-limit",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Chandrasekhar limit"
      },
      "definition": {
        "modality": "text",
        "value": "The heaviest a white dwarf can be, about 1.4 solar masses — a ceiling on the leftover core rather than on the star it came from, set by where electron degeneracy pressure loses to gravity"
      },
      "curatedDistractors": [
        "Tolman-Oppenheimer-Volkoff limit",
        "Electron degeneracy pressure",
        "Photodisintegration"
      ],
      "source": {
        "label": "NASA Imagine the Universe — The Life Cycles of Stars",
        "url": "https://imagine.gsfc.nasa.gov/educators/lifecycles/LC_main3.html"
      },
      "tags": [
        "l12p3",
        "white-dwarf",
        "vocabulary"
      ],
      "uid": "1tijnlbsubgwd"
    },
    {
      "id": "ast-q-sun-black-hole-mass",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "How much heavier would the Sun need to be to end as a black hole?"
      },
      "options": [
        {
          "modality": "text",
          "value": "About 20 times its mass"
        },
        {
          "modality": "text",
          "value": "About 50 times its mass"
        },
        {
          "modality": "text",
          "value": "About 3 times its mass"
        },
        {
          "modality": "text",
          "value": "About 12 times its mass"
        }
      ],
      "correctIndex": 0,
      "explanation": "NASA puts it at about 20 times the Sun's mass. Three is a limit on the leftover CORE, not the star that made it. Twelve would give a supernova, but the core left behind would settle as a neutron star. Fifty would do it — the question asks the least it would take.",
      "source": {
        "label": "NASA — Why the Sun Won't Become a Black Hole",
        "url": "https://www.nasa.gov/image-article/why-sun-wont-become-black-hole/"
      },
      "tags": [
        "l12p3",
        "black-hole",
        "quiz"
      ],
      "uid": "1lq6771og5rfz"
    },
    {
      "id": "ast-q-supernova-energy-carrier",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "What carries away about 99 percent of a core-collapse supernova's energy?"
      },
      "options": [
        {
          "modality": "text",
          "value": "The expanding debris"
        },
        {
          "modality": "text",
          "value": "Visible light"
        },
        {
          "modality": "text",
          "value": "X-rays"
        },
        {
          "modality": "text",
          "value": "Neutrinos"
        }
      ],
      "correctIndex": 3,
      "explanation": "They leave in a burst roughly ten seconds long, passing straight through everything in their path. The visible flash, the X-rays and the expanding debris share the remaining one percent between them — the light show is the leftover, not the explosion.",
      "source": {
        "label": "Fermilab — All Things Neutrino: Supernova Neutrinos",
        "url": "https://neutrinos.fnal.gov/sources/supernova-neutrinos/"
      },
      "tags": [
        "l12p3",
        "supernova",
        "quiz"
      ],
      "uid": "16r7cms15usx0k"
    },
    {
      "id": "ast-q-core-gives-way-iron",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Why does a massive star's core give way at the end?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Its outer layers crush it"
        },
        {
          "modality": "text",
          "value": "It spins itself apart"
        },
        {
          "modality": "text",
          "value": "Fusing iron would cost energy"
        },
        {
          "modality": "text",
          "value": "It has no fuel left at all"
        }
      ],
      "correctIndex": 2,
      "explanation": "Iron is where fusion stops paying: its nuclear structure means fusing it yields no net energy. The core is not empty — it is full of iron it cannot afford to burn. The outer layers fall in only after the support beneath them vanishes, and spin plays no part.",
      "source": {
        "label": "CSIRO ATNF — The Death of Stars II: High-Mass Stars",
        "url": "https://www.atnf.csiro.au/resources/education/senior-astrophysics/stellarevolution/deathhigh/"
      },
      "tags": [
        "l12p3",
        "supernova",
        "quiz"
      ],
      "uid": "p8rj7y1wt2zys"
    },
    {
      "id": "ast-c-white-dwarf-remnant",
      "shape": "concept",
      "conceptKind": "thing",
      "name": "White dwarf",
      "clues": [
        "The lightest of the three objects a collapsed stellar core can end up as.",
        "It is the ending for a leftover core below about 1.4 solar masses; a heavier core cannot stop there.",
        "What holds it against gravity is electron degeneracy pressure, and NASA puts the ceiling on that pressure at 1.44 solar masses."
      ],
      "source": {
        "label": "NASA Imagine the Universe — Background: Life Cycles of Stars",
        "url": "https://imagine.gsfc.nasa.gov/educators/lessons/xray_spectra/background-lifecycles.html"
      },
      "tags": [
        "l12p3",
        "remnants",
        "thing"
      ],
      "uid": "gccxwt1kxe3fx"
    },
    {
      "id": "ast-c-neutron-star-remnant",
      "shape": "concept",
      "conceptKind": "thing",
      "name": "Neutron star",
      "clues": [
        "The middle of the three possible endings: what a leftover core between roughly 1.4 and 3 solar masses becomes.",
        "More than the Sun's mass inside a sphere about 20 kilometres across; a sugar cube of the material would weigh about a billion tons.",
        "NASA's NICER mission sized a 2.1-solar-mass example at roughly 25 to 27 kilometres wide, depending on which analysis team's model you take."
      ],
      "source": {
        "label": "NASA Imagine the Universe — Neutron Stars",
        "url": "https://imagine.gsfc.nasa.gov/science/objects/neutron_stars1.html"
      },
      "tags": [
        "l12p3",
        "remnants",
        "thing"
      ],
      "uid": "1lztrqlgt2sz3"
    },
    {
      "id": "ast-c-black-hole-remnant",
      "shape": "concept",
      "conceptKind": "thing",
      "name": "Black hole",
      "clues": [
        "The heaviest of the three possible endings: what a leftover core above about 3 solar masses becomes",
        "NASA says our own star would need to be roughly 20 times more massive to finish this way",
        "Not even light escapes once the core passes the limit that neutron pressure can hold"
      ],
      "source": {
        "label": "NASA Imagine the Universe — Background: Life Cycles of Stars",
        "url": "https://imagine.gsfc.nasa.gov/educators/lessons/xray_spectra/background-lifecycles.html"
      },
      "tags": [
        "l12p3",
        "remnants",
        "thing"
      ],
      "uid": "1mmcmci19x050o"
    },
    {
      "id": "ast-c-core-collapse-supernova",
      "shape": "concept",
      "conceptKind": "thing",
      "name": "Core-collapse supernova",
      "clues": [
        "About 10^46 joules released in a matter of seconds — some 50 times more than the Sun will put out in 10 billion years.",
        "It is not a star running out of fuel — it is a star whose remaining fuel would cost more energy to burn than it gives back.",
        "The blinding flash everyone points a telescope at is only about one percent of what it releases; the rest leaves invisibly."
      ],
      "source": {
        "label": "Fermilab — All Things Neutrino: Supernova Neutrinos",
        "url": "https://neutrinos.fnal.gov/sources/supernova-neutrinos/"
      },
      "tags": [
        "l12p3",
        "supernova",
        "thing"
      ],
      "uid": "rb2rz21gfmuhg"
    },
    {
      "id": "ast-c-supernova-neutrinos",
      "shape": "concept",
      "conceptKind": "thing",
      "name": "Neutrinos",
      "clues": [
        "Particles that carry away roughly 99 percent of the energy of an exploding massive star, in a burst about ten seconds long.",
        "They pass straight through everything in their path — the dying star's own outer layers, the Earth, and you — which is why so few are ever caught.",
        "Just 25 of them were caught on Earth from a single such event in 1987."
      ],
      "source": {
        "label": "Fermilab — All Things Neutrino: Supernova Neutrinos",
        "url": "https://neutrinos.fnal.gov/sources/supernova-neutrinos/"
      },
      "tags": [
        "l12p3",
        "supernova",
        "thing"
      ],
      "uid": "o4ldjq1b0ti3i"
    },
    {
      "id": "ast-c-iron-shell-element",
      "shape": "concept",
      "conceptKind": "thing",
      "name": "Iron",
      "clues": [
        "The last element a massive star manages to build in its shells, and the point at which its engine stops paying.",
        "Fusing it yields no net energy — because of its nuclear structure, the reaction costs energy instead of releasing it.",
        "Around 10 billion K it comes apart under the radiation around it, the support beneath the star's outer layers disappears, and what is left falls inward at tens of thousands of kilometres per second."
      ],
      "source": {
        "label": "CSIRO ATNF — The Death of Stars II: High-Mass Stars",
        "url": "https://www.atnf.csiro.au/resources/education/senior-astrophysics/stellarevolution/deathhigh/"
      },
      "tags": [
        "l12p3",
        "supernova",
        "thing"
      ],
      "uid": "1jqgnv9kyhphn"
    },
    {
      "id": "tfr-ast-d-chandrasekhar-limit",
      "shape": "trueFalse",
      "derivedFrom": "ast-d-chandrasekhar-limit",
      "statement": "Chandrasekhar limit — how much atmosphere a beam crosses on its way down.",
      "isTrue": false,
      "why": "Airmass is how much atmosphere a beam crosses on its way down, the reason a star low over the horizon looks dimmer and redder. The Chandrasekhar limit is a mass ceiling: the heaviest a white dwarf can be, about 1.4 solar masses, beyond which it cannot hold itself up.",
      "source": {
        "label": "NASA Imagine the Universe — The Life Cycles of Stars",
        "url": "https://imagine.gsfc.nasa.gov/educators/lifecycles/LC_main3.html"
      },
      "tags": [
        "l12p3",
        "white-dwarf",
        "vocabulary",
        "derived"
      ],
      "whyOptions": [
        "Airmass",
        "Apparent magnitude",
        "Solar mass"
      ],
      "whyCorrectIndex": 0,
      "uid": "i6zsyqxah8ty"
    },
    {
      "id": "ast-f-milky-way-thin-disc",
      "shape": "fact",
      "title": "A Hundred Times Wider",
      "body": "We live inside a **barred spiral**: a flat disc of stars with spiral arms and a straight **bar** of stars crossing the centre. About **two-thirds** of spirals are barred, so a bar is the normal condition, not a curiosity. The disc runs about **100,000 light-years** across but is astonishingly shallow — a **thin disc** some **700 light-years** high sitting inside a **thick disc** about 3,000 light-years high. Roughly a hundred times wider than it is deep, which is why the galaxy shows up as a narrow band across the sky rather than a glow in every direction.",
      "factVariant": "image-heavy",
      "imageCaption": "A hundred times wider than it is deep — which is why it reads as a band, not a ball.",
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "Milky Way barred spiral face-on and edge-on structure diagram thin disc thick disc",
        "imagePrompt": "Flat vector diagram with a face-on barred spiral labelled with the bar and arms, and beside it an edge-on cross-section showing a 700-light-year thin disc inside a 3,000-light-year thick disc, both drawn to scale against the 100,000-light-year width.",
        "alt": "Two-view diagram of the Milky Way: a barred spiral face-on, and edge-on a disc 100,000 light-years wide but only hundreds deep",
        "depictable": true,
        "allowGenerated": true
      },
      "source": {
        "label": "NASA Imagine the Universe — Milky Way Galaxy",
        "url": "https://imagine.gsfc.nasa.gov/science/objects/milkyway1.html"
      },
      "tags": [
        "l13p1",
        "milky-way",
        "structure"
      ],
      "uid": "uq15zs1p7p4im"
    },
    {
      "id": "ast-f-sun-galactic-orbit",
      "shape": "fact",
      "title": "Halfway Out, Still Turning",
      "body": "The Sun is not at the centre and not on the rim. It sits about **26,000 light-years** from the galactic middle — published values run from 25,000 to 27,000 — roughly **halfway out** to the edge of the disc. And it is not parked there. One lap around the galactic centre takes about **250 million years**, longer than the entire history of the dinosaurs. Stars are not fixed while only planets move: the whole disc turns, and we turn with it.",
      "source": {
        "label": "NASA Imagine the Universe — Milky Way Galaxy",
        "url": "https://imagine.gsfc.nasa.gov/science/objects/milkyway1.html"
      },
      "tags": [
        "l13p1",
        "milky-way",
        "orbit"
      ],
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "Sun position 26,000 light-years from the galactic centre annotated Milky Way map",
        "imagePrompt": "Flat vector face-on map of the Milky Way with spiral arms and central bar, the Sun marked with a labelled radius of about 26,000 light-years and an arrow for its 250-million-year orbit.",
        "alt": "Annotated map of the Milky Way with the Sun marked about 26,000 light-years out, roughly halfway to the edge of the disc",
        "depictable": true,
        "allowGenerated": true
      },
      "uid": "nkn25t1k41thh"
    },
    {
      "id": "ast-f-milky-way-star-count",
      "shape": "fact",
      "title": "Nobody Has Counted Them",
      "body": "The Milky Way holds **on the order of one hundred billion** stars — and reputable sources stretch that to **a few hundred billion**. The range is not caution for its own sake. Nobody has counted them: the total is **inferred** from the galaxy's mass and its light, which is why careful sources disagree with each other by a factor of a few and none of them can do better.",
      "source": {
        "label": "NASA Imagine the Universe — Milky Way Galaxy",
        "url": "https://imagine.gsfc.nasa.gov/science/objects/milkyway1.html"
      },
      "tags": [
        "l13p1",
        "milky-way",
        "stars"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "the Milky Way band arching over a dark landscape",
        "entityTerm": "Milky Way",
        "imagePrompt": "A wide night photograph of the Milky Way arching across the sky above a dark, low landscape, its dust lanes visible against the glow.",
        "alt": "A night-sky panorama of the Milky Way arching as a bright, dust-laned band over a rocky mountain ridge, with a stone-paved footpath and railings climbing toward a rock outcrop and cloud below the…",
        "depictable": true,
        "credit": "Unsplash · Sebastian Knoll · Unsplash License",
        "creditUrl": "https://unsplash.com/photos/milky-way-arching-over-a-rocky-mountain-path-IPCh5x1whiQ",
        "subject": "A night-sky panorama of the Milky Way arching as a bright, dust-laned band over a rocky mountain ridge, with a stone-paved footpath and railings climbing toward a rock outcrop and cloud below the peaks (the trail resembles the Pico do Arieiro–Pico Ruivo route on Madeira).",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-milky-way-star-count.webp"
      },
      "uid": "r5p41l551t0"
    },
    {
      "id": "ast-f-sagittarius-a-star",
      "shape": "fact",
      "title": "Four Million Suns",
      "body": "At the centre sits Sagittarius A*, a **supermassive black hole** of about **four million solar masses**. That mass was measured the way a planet's is — from the orbits of things around it. The star **S2** goes round every **16 years**, and at closest approach its light is stretched to longer wavelengths by exactly the amount **general relativity** predicts. Four million Suns is still a small share of a galaxy of a hundred billion stars, and the Sun orbits it as calmly as Earth orbits the Sun.",
      "factVariant": "image-heavy",
      "imageCaption": "S2 laps the galactic centre every sixteen years, and its light reddens exactly on cue.",
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "S2 star orbit around Sagittarius A star diagram galactic centre",
        "imagePrompt": "Flat vector diagram of the elongated orbit of the star S2 around an unseen central mass, observed positions plotted by year with the pericentre passage marked.",
        "alt": "Diagram of S2's sixteen-year orbit around Sagittarius A*, the measurement that weighed the black hole at four million suns",
        "depictable": true,
        "allowGenerated": true
      },
      "source": {
        "label": "ESO — Astronomers reveal first image of the black hole at the heart of our galaxy (eso2208)",
        "url": "https://www.eso.org/public/news/eso2208-eht-mw/"
      },
      "tags": [
        "l13p1",
        "milky-way",
        "black-hole"
      ],
      "uid": "2y0tr31sznnkh"
    },
    {
      "id": "ast-p-lenticular-galaxy",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Lenticular galaxy (S0)"
      },
      "sideB": {
        "modality": "text",
        "value": "A bulge and disc, but no spiral arms"
      },
      "source": {
        "label": "NASA Science — Galaxy Types",
        "url": "https://science.nasa.gov/universe/galaxies/types/"
      },
      "tags": [
        "l13p1",
        "galaxies",
        "classification"
      ],
      "uid": "11agb8tht2x0z"
    },
    {
      "id": "ast-p-elliptical-galaxy",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Elliptical galaxy"
      },
      "sideB": {
        "modality": "text",
        "value": "A round-to-oval swarm built by mergers of spirals",
        "short": "Round to oval, built by mergers"
      },
      "source": {
        "label": "NASA Science — Galaxy Types",
        "url": "https://science.nasa.gov/universe/galaxies/types/"
      },
      "tags": [
        "l13p1",
        "galaxies",
        "classification"
      ],
      "uid": "1bpytdkwqdkdk"
    },
    {
      "id": "ast-d-irregular-galaxy",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Irregular galaxy"
      },
      "definition": {
        "modality": "text",
        "value": "A galaxy with no disc, no arms and no smooth ellipse — the ragged fourth category the tuning fork cannot hold"
      },
      "source": {
        "label": "NASA Science — Galaxy Types",
        "url": "https://science.nasa.gov/universe/galaxies/types/"
      },
      "tags": [
        "l13p1",
        "galaxies",
        "classification"
      ],
      "uid": "y96viz1bxfp0v"
    },
    {
      "id": "ast-q-eht-image-content",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "What does the 2022 image of the Milky Way's centre actually show?"
      },
      "options": [
        {
          "modality": "text",
          "value": "A shadow ringed by glowing gas"
        },
        {
          "modality": "text",
          "value": "An artist's impression of it"
        },
        {
          "modality": "text",
          "value": "A photograph of the hole itself"
        },
        {
          "modality": "text",
          "value": "A computer simulation of it"
        }
      ],
      "correctIndex": 0,
      "explanation": "A black hole emits no light, so it cannot be photographed. The Event Horizon Telescope assembled real 2017 data from eight radio observatories linked into one Earth-sized instrument — neither an impression nor a simulation. The dark centre is a silhouette.",
      "source": {
        "label": "ESO — Astronomers reveal first image of the black hole at the heart of our galaxy (eso2208)",
        "url": "https://www.eso.org/public/news/eso2208-eht-mw/"
      },
      "tags": [
        "l13p1",
        "milky-way",
        "black-hole"
      ],
      "uid": "5h1b89l2zih3"
    },
    {
      "id": "ast-q-hubble-tuning-fork",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "What do the labels on Hubble's tuning fork actually record?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Shape, as seen from Earth"
        },
        {
          "modality": "text",
          "value": "A galaxy's distance"
        },
        {
          "modality": "text",
          "value": "A galaxy's age"
        },
        {
          "modality": "text",
          "value": "A stage of galaxy evolution"
        }
      ],
      "correctIndex": 0,
      "explanation": "E0 to E7 encodes roundness, Sa to Sc encodes how tightly the arms wind, and a B marks a bar — appearance and nothing else. Age and distance are nowhere on the diagram, and galaxies do not march along it: 'early' and 'late' are a surviving misnomer.",
      "source": {
        "label": "ESA/Hubble — The Hubble tuning fork: classification of galaxies",
        "url": "https://sci.esa.int/web/hubble/-/52791-the-hubble-tuning-fork-classification-of-galaxies"
      },
      "tags": [
        "l13p1",
        "galaxies",
        "classification"
      ],
      "uid": "kpfeu51o2xg8l"
    },
    {
      "id": "tfr-ast-d-irregular-galaxy",
      "shape": "trueFalse",
      "derivedFrom": "ast-d-irregular-galaxy",
      "statement": "Irregular galaxy — a galaxy with no disc, no arms and no smooth ellipse.",
      "isTrue": true,
      "why": "An ice giant is a giant planet whose bulk is a hot fluid of water, methane and ammonia over a rocky core, not the hydrogen and helium of a gas giant. An irregular galaxy is a galaxy with no disc, no arms and no smooth ellipse, often pulled about by a larger neighbour.",
      "source": {
        "label": "NASA Science — Galaxy Types",
        "url": "https://science.nasa.gov/universe/galaxies/types/"
      },
      "tags": [
        "l13p1",
        "galaxies",
        "classification",
        "derived"
      ],
      "uid": "px78hm1m57jee"
    },
    {
      "id": "ast-f-light-year-is-distance",
      "shape": "fact",
      "title": "A Distance, Not a Duration",
      "body": "A **light-year** is a distance. Light crosses space at **186,000 miles — 300,000 km — per second**, and in one year it covers about **9.46 trillion kilometres**, or 5.88 trillion miles. That is what the word measures: how far, not how long. The reason it sounds like a time is that in astronomy a distance and a lookback time are the same statement — light that has travelled four light-years also left four years ago.",
      "factVariant": "image-heavy",
      "imageCaption": "The unit that makes galactic distances sayable measures kilometres, not years.",
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "light-year as a distance diagram light travelling for one year",
        "imagePrompt": "Flat vector diagram of a ruler-like distance axis with a light ray travelling along it, annotated 300,000 km/s and terminating at a labelled 9.46 trillion km after one year.",
        "alt": "Diagram of a light-year as a distance: 300,000 km every second, for a year, reaching about 9.46 trillion kilometres",
        "depictable": true,
        "allowGenerated": true
      },
      "source": {
        "label": "NASA Science — What is a light-year?",
        "url": "https://science.nasa.gov/exoplanets/what-is-a-light-year/"
      },
      "tags": [
        "l13p2",
        "distance",
        "units"
      ],
      "uid": "4mt9nz1nvmz71"
    },
    {
      "id": "ast-f-distance-ladder-rungs",
      "shape": "fact",
      "title": "Three Rungs, One Ladder",
      "body": "No single method reaches every distance, so the **cosmic distance ladder** stacks them. **Parallax** is the bottom rung and the only purely geometric one: as Earth swings to the far side of its orbit, a nearby star shifts against the background, and trigonometry does the rest. **Cepheid variables** pulse at a rate tied to their true brightness. **Type Ia supernovae** all peak near the same brightness and reach roughly **1,000 times farther** than Cepheids. Each rung is calibrated by the one below it, so an error low down travels all the way up.",
      "source": {
        "label": "NASA Science — Three Steps to the Hubble Constant",
        "url": "https://science.nasa.gov/asset/hubble/three-steps-to-the-hubble-constant/"
      },
      "tags": [
        "l13p2",
        "distance",
        "ladder"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Gaia spacecraft ESA astrometry mission",
        "entityTerm": "Gaia (spacecraft)",
        "imagePrompt": "A photograph or engineering image of ESA's Gaia spacecraft showing its wide circular sunshield beneath the compact instrument module.",
        "alt": "Gaia, the spacecraft that measures the bottom rung of the distance ladder by pure geometry",
        "depictable": true,
        "credit": "Wikipedia — Gaia (spacecraft) · See Wikimedia Commons",
        "creditUrl": "https://en.wikipedia.org/wiki/Gaia_(spacecraft)",
        "subject": "ESA's official artist's-impression/composite image of the actual Gaia spacecraft (flat circular sunshield beneath a cylindrical payload module) silhouetted against the real Milky Way — the lead image of Wikipedia's 'Gaia (spacecraft)' article.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-distance-ladder-rungs.webp"
      },
      "uid": "8erl2u1il85jg"
    },
    {
      "id": "ast-f-andromeda-approaching",
      "shape": "fact",
      "title": "The Galaxy Coming Toward Us",
      "body": "Almost every galaxy is receding. **Andromeda** is not. It lies about **2.5 million light-years** away and is closing at roughly **250,000 miles per hour**, so its spectral lines sit at *shorter* wavelengths — **blueshifted**, which is unusual among galaxies. Both belong to the **Local Group**, a gravitationally bound crowd of more than 30 galaxies spread across some 10 million light-years, and inside a bound group local gravity beats cosmic expansion.",
      "source": {
        "label": "NASA — Hubble Shows Milky Way is Destined for Head-On Collision",
        "url": "https://science.nasa.gov/missions/hubble/nasas-hubble-shows-milky-way-is-destined-for-head-on-collision/"
      },
      "tags": [
        "l13p2",
        "andromeda",
        "local-group"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "Andromeda Galaxy M31 photograph",
        "entityTerm": "Andromeda Galaxy",
        "imagePrompt": "A wide-field astronomical photograph of the Andromeda Galaxy showing its bright nucleus, tilted spiral disc, dust lanes and companion galaxies.",
        "alt": "A wide-field astrophotograph of the Andromeda Galaxy (M31): an inclined spiral with a bright yellow-white core, dark dust lanes and blue outer arms, with its satellite galaxies M32 (compact, just…",
        "depictable": true,
        "credit": "Wikipedia — Andromeda Galaxy · See Wikimedia Commons",
        "creditUrl": "https://en.wikipedia.org/wiki/Andromeda_Galaxy",
        "subject": "A wide-field astrophotograph of the Andromeda Galaxy (M31): an inclined spiral with a bright yellow-white core, dark dust lanes and blue outer arms, with its satellite galaxies M32 (compact, just above the disk near the core) and M110 (diffuse, below the disk) against a dense star field.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-andromeda-approaching.webp"
      },
      "uid": "16f5r47l76u5x"
    },
    {
      "id": "ast-f-andromeda-merger-open",
      "shape": "fact",
      "title": "The Collision Is Not Settled",
      "body": "The Milky Way–Andromeda collision is usually quoted as a fact with a date. It is not one. Hubble measurements in **2012** predicted a collision in about **4 billion years** and a single merged galaxy by about 6 billion. A **2025** analysis in *Nature Astronomy*, using Gaia and Hubble data, found close to a **50 percent chance of no merger at all** within the next 10 billion years. Better data made the answer less certain, not more.",
      "source": {
        "label": "NASA Science — Crash of the Titans: Andromeda Galaxy and the Milky Way Collision",
        "url": "https://science.nasa.gov/asset/hubble/crash-of-the-titans-andromeda-galaxy-and-the-milky-way-collision/"
      },
      "tags": [
        "l13p2",
        "andromeda",
        "open-question"
      ],
      "uid": "envtu7jf3btf"
    },
    {
      "id": "ast-p-parallax-rung",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Parallax"
      },
      "sideB": {
        "modality": "text",
        "value": "The shift of a nearby star as Earth changes side"
      },
      "source": {
        "label": "ESA/Gaia — Parallax",
        "url": "https://www.esa.int/Science_Exploration/Space_Science/Gaia/Parallax"
      },
      "tags": [
        "l13p2",
        "distance",
        "ladder"
      ],
      "uid": "gpcuhxx5l1e7"
    },
    {
      "id": "ast-d-standard-candle",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Standard candle"
      },
      "definition": {
        "modality": "text",
        "value": "An object whose true brightness can be worked out from something observable about it, so comparing that with how bright it looks gives its distance"
      },
      "curatedDistractors": [
        "Parallax",
        "Redshift",
        "Light-year"
      ],
      "source": {
        "label": "ESA/Hubble — Cosmic distance ladder",
        "url": "https://sci.esa.int/web/hubble/-/57875-cosmic-distance-ladder"
      },
      "tags": [
        "l13p2",
        "distance",
        "ladder"
      ],
      "uid": "vy5zfec2i7aq"
    },
    {
      "id": "ast-q-parsec-definition",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "How is a parsec defined?"
      },
      "options": [
        {
          "modality": "text",
          "value": "A one-arcsecond parallax shift"
        },
        {
          "modality": "text",
          "value": "A year of travel at light speed"
        },
        {
          "modality": "text",
          "value": "One trillion kilometres exactly"
        },
        {
          "modality": "text",
          "value": "The width of Earth's orbit"
        }
      ],
      "correctIndex": 0,
      "explanation": "A parsec is the distance at which a star's parallax would be exactly one arcsecond — about 3.26 light-years, or roughly 31 trillion kilometres, not one. Earth's orbit is the baseline that produces the shift, not the unit, and a year of light travel is a light-year.",
      "source": {
        "label": "ESA/Gaia — Cosmic distances",
        "url": "https://www.esa.int/Science_Exploration/Space_Science/Gaia/Cosmic_distances"
      },
      "tags": [
        "l13p2",
        "distance",
        "units"
      ],
      "uid": "1rgqslx1vovefp"
    },
    {
      "id": "ast-q-galaxy-merger-stars",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "If the Milky Way and Andromeda merge, what happens to their stars?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Most of them smash together"
        },
        {
          "modality": "text",
          "value": "They merge into larger stars"
        },
        {
          "modality": "text",
          "value": "Almost all of them sail past"
        },
        {
          "modality": "text",
          "value": "They are torn apart by gravity"
        }
      ],
      "correctIndex": 2,
      "explanation": "A galaxy is mostly empty space: stars are separated by distances vastly greater than their own size, which rules out the smashing, the merging and the tearing alike. What a galactic encounter rearranges is orbits, over hundreds of millions of years.",
      "source": {
        "label": "NASA — Hubble Shows Milky Way is Destined for Head-On Collision",
        "url": "https://science.nasa.gov/missions/hubble/nasas-hubble-shows-milky-way-is-destined-for-head-on-collision/"
      },
      "tags": [
        "l13p2",
        "andromeda",
        "collision"
      ],
      "uid": "nk4f1c16ip4tg"
    },
    {
      "id": "ast-n-ly-parsec",
      "shape": "numeric",
      "prompt": {
        "modality": "text",
        "value": "One parsec, expressed in light-years"
      },
      "value": 3.26,
      "unit": "light-year",
      "tolerance": 0.05,
      "source": {
        "label": "ESA/Gaia — Cosmic distances",
        "url": "https://www.esa.int/Science_Exploration/Space_Science/Gaia/Cosmic_distances"
      },
      "tags": [
        "l13p2",
        "distance",
        "units"
      ],
      "uid": "17ajcr81dfa00u"
    },
    {
      "id": "ast-n-ly-thin-disc-height",
      "shape": "numeric",
      "prompt": {
        "modality": "text",
        "value": "Height of the Milky Way's thin disc"
      },
      "value": 700,
      "unit": "light-year",
      "tolerance": 100,
      "source": {
        "label": "ESA/Gaia — Anatomy of the Milky Way",
        "url": "https://sci.esa.int/web/gaia/-/58206-anatomy-of-the-milky-way"
      },
      "tags": [
        "l13p2",
        "distance",
        "milky-way"
      ],
      "uid": "1sf06u714vuf03"
    },
    {
      "id": "ast-n-ly-sun-to-centre",
      "shape": "numeric",
      "prompt": {
        "modality": "text",
        "value": "The Sun's distance from the galactic centre"
      },
      "value": 26000,
      "unit": "light-year",
      "tolerance": 1500,
      "source": {
        "label": "NASA Imagine the Universe — Milky Way Galaxy",
        "url": "https://imagine.gsfc.nasa.gov/science/objects/milkyway1.html"
      },
      "tags": [
        "l13p2",
        "distance",
        "milky-way"
      ],
      "uid": "kvjqmyk1j088"
    },
    {
      "id": "ast-n-ly-milky-way-width",
      "shape": "numeric",
      "prompt": {
        "modality": "text",
        "value": "Width of the Milky Way's disc"
      },
      "value": 100000,
      "unit": "light-year",
      "tolerance": 10000,
      "source": {
        "label": "NASA Imagine the Universe — Milky Way Galaxy",
        "url": "https://imagine.gsfc.nasa.gov/science/objects/milkyway1.html"
      },
      "tags": [
        "l13p2",
        "distance",
        "milky-way"
      ],
      "uid": "1hbe1pt16fjsav"
    },
    {
      "id": "ast-n-ly-andromeda-distance",
      "shape": "numeric",
      "prompt": {
        "modality": "text",
        "value": "Distance to the Andromeda galaxy"
      },
      "value": 2500000,
      "unit": "light-year",
      "tolerance": 200000,
      "source": {
        "label": "NASA — Hubble Shows Milky Way is Destined for Head-On Collision",
        "url": "https://science.nasa.gov/missions/hubble/nasas-hubble-shows-milky-way-is-destined-for-head-on-collision/"
      },
      "tags": [
        "l13p2",
        "distance",
        "andromeda"
      ],
      "uid": "101pg5ttswbfr"
    },
    {
      "id": "ast-n-ly-local-group-span",
      "shape": "numeric",
      "prompt": {
        "modality": "text",
        "value": "Width of the Local Group of galaxies"
      },
      "value": 10000000,
      "unit": "light-year",
      "tolerance": 2000000,
      "source": {
        "label": "NASA Imagine the Universe — Local Group galaxies",
        "url": "https://imagine.gsfc.nasa.gov/features/cosmic/local_group_info.html"
      },
      "tags": [
        "l13p2",
        "distance",
        "local-group"
      ],
      "uid": "1jm0swu3wdghs"
    },
    {
      "id": "ast-f-spacetime-curvature",
      "shape": "fact",
      "title": "Straight Lines Through Bent Space",
      "body": "**General relativity** does away with gravity as a force. Mass and energy **curve spacetime**, and everything — including **light**, which has no mass — simply follows the curvature. Earth is not held on an invisible rope by the Sun; it is travelling as straight as it can through a region that is bent. That is also why a photon is deflected near a massive object: nothing tugs on it, because there is nothing to tug on. The geometry it crosses is what is bent.",
      "factVariant": "image-heavy",
      "imageCaption": "An orbit is a straight line — through a geometry that has been bent.",
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "curved spacetime grid around a massive body general relativity diagram",
        "imagePrompt": "Flat vector diagram of a rectangular grid deformed into a depression around a central mass, with a smaller body and a light ray each following the bent grid lines rather than a straight path.",
        "alt": "Diagram of a mass deforming a spacetime grid, with a nearby body simply following the curve rather than being pulled",
        "depictable": true,
        "allowGenerated": true
      },
      "source": {
        "label": "NASA Imagine the Universe — Ask an Astrophysicist: relativity",
        "url": "https://imagine.gsfc.nasa.gov/ask_astro/relativity.html"
      },
      "tags": [
        "l13p3",
        "relativity",
        "spacetime"
      ],
      "uid": "35ktecwhkqzi"
    },
    {
      "id": "ast-f-gravitational-lensing-arcs",
      "shape": "fact",
      "title": "Arcs of a Single Galaxy",
      "body": "**Gravitational lensing** is the prediction you can photograph. A massive foreground object — typically a **galaxy cluster** — curves spacetime enough to bend, distort and magnify the light of whatever lies behind it, sometimes producing several images of one background galaxy, and in perfect alignment a complete **Einstein ring**. The arcs are not separate objects and not a telescope artefact. They are one galaxy, imaged more than once by the mass sitting in front of it.",
      "factVariant": "image-heavy",
      "imageCaption": "Those arcs are not a row of galaxies. They are one galaxy, imaged several times over.",
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "galaxy cluster gravitational lensing arcs Einstein ring Hubble image",
        "entityTerm": "Gravitational lens",
        "imagePrompt": "A Hubble-style image of a massive galaxy cluster with elongated blue arcs of lensed background galaxies curving concentrically around its centre.",
        "alt": "Hubble image of galaxy cluster SDSS J1038+4849, the \"smiling\" cluster: two bright orange elliptical cluster galaxies at centre with thin blue gravitationally lensed arcs of background galaxies…",
        "depictable": true,
        "credit": "NASA/ESA · Public domain",
        "creditUrl": "https://commons.wikimedia.org/wiki/File:HST-Smiling-GalaxyClusterSDSS-J1038%2B4849-20150210.jpg",
        "subject": "Hubble image of galaxy cluster SDSS J1038+4849, the \"smiling\" cluster: two bright orange elliptical cluster galaxies at centre with thin blue gravitationally lensed arcs of background galaxies curving around and below them into a near-complete ring, against a field of fainter galaxies.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-gravitational-lensing-arcs.webp"
      },
      "source": {
        "label": "ESA/Hubble Wordbank — Gravitational lensing",
        "url": "https://esahubble.org/wordbank/gravitational-lensing/"
      },
      "tags": [
        "l13p3",
        "relativity",
        "lensing"
      ],
      "uid": "1u01au0l0ylw6"
    },
    {
      "id": "ast-f-gps-relativity-correction",
      "shape": "fact",
      "title": "Relativity in Your Pocket",
      "body": "A **GPS** satellite clock runs about **45 microseconds a day fast** because it sits in weaker gravity, and about **7 microseconds a day slow** because of its orbital speed — a net gain near **38 microseconds a day**. The two effects pull in opposite directions and the system corrects for both. Left uncorrected, positions would drift by roughly **10 kilometres a day**. Relativity is not confined to black holes; it is a working engineering correction in hardware you carry around.",
      "source": {
        "label": "Ohio State University Astronomy 162 — Real-World Relativity: The GPS Navigation System",
        "url": "https://www.astronomy.ohio-state.edu/pogge.1/Ast162/Unit5/gps.html"
      },
      "tags": [
        "l13p3",
        "relativity",
        "gps"
      ],
      "illustration": {
        "kind": "photo",
        "imageSearchTerm": "GPS navigation satellite spacecraft in orbit",
        "entityTerm": "Global Positioning System",
        "imagePrompt": "An illustration or photograph of a GPS navigation satellite with solar panels extended and antenna array facing Earth.",
        "alt": "A GPS satellite, whose onboard clock has to be corrected for relativity by 38 microseconds a day",
        "depictable": true,
        "credit": "Wikipedia — Global Positioning System · See Wikimedia Commons",
        "creditUrl": "https://en.wikipedia.org/wiki/Global_Positioning_System",
        "subject": "Artist rendering of a GPS Block IIIA navigation satellite with Earth below; this is the actual lead/infobox image of Wikipedia's 'Global Positioning System' article — a real GPS satellite type, correctly and specifically identified.",
        "url": "https://cdn.recurxive.com/packs/astronomy-and-space/images/ast-f-gps-relativity-correction.webp"
      },
      "uid": "1m2tzyd1h3c2m1"
    },
    {
      "id": "ast-f-hubble-tension-gap",
      "shape": "fact",
      "title": "The Rate Nobody Agrees On",
      "body": "Everyone agrees the universe expands. Nobody agrees how fast. Distance-ladder measurements give an expansion rate of about **70–76 km/s per megaparsec**; measurements of the **cosmic microwave background** give about **67.4**. Both camps have checked their work — Webb observations have ruled out simple measurement error — and the two ranges still do not overlap. This is the **Hubble tension**: either one method hides an unknown systematic, or the standard cosmological model is missing something.",
      "source": {
        "label": "NASA Science — Hubble Constant and Tension",
        "url": "https://science.nasa.gov/mission/hubble/science/science-behind-the-discoveries/hubble-constant-and-tension/"
      },
      "tags": [
        "l13p3",
        "cosmology",
        "open-question"
      ],
      "illustration": {
        "kind": "diagram",
        "imageSearchTerm": "Hubble tension diagram distance ladder versus cosmic microwave background expansion rate",
        "imagePrompt": "Flat vector diagram with a single horizontal axis in km/s per megaparsec carrying two clearly separated measurement points with error bars, one labelled distance ladder near 73 and one labelled CMB near 67.4.",
        "alt": "Diagram of the two expansion-rate measurements with their error bars — around 73 and around 67.4, and no overlap",
        "depictable": true,
        "allowGenerated": true
      },
      "uid": "1e5rqwjxh7m1f"
    },
    {
      "id": "ast-p-cosmological-redshift",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Cosmological redshift"
      },
      "sideB": {
        "modality": "text",
        "value": "Light stretched by space expanding in transit"
      },
      "source": {
        "label": "ESA — What is 'red shift'?",
        "url": "https://www.esa.int/Science_Exploration/Space_Science/What_is_red_shift"
      },
      "tags": [
        "l13p3",
        "cosmology",
        "expansion"
      ],
      "uid": "11a805c2zz3f8"
    },
    {
      "id": "ast-p-einstein-ring",
      "shape": "pair",
      "sideA": {
        "modality": "text",
        "value": "Einstein ring"
      },
      "sideB": {
        "modality": "text",
        "value": "A background galaxy smeared into a full circle"
      },
      "source": {
        "label": "ESA/Hubble Wordbank — Gravitational lensing",
        "url": "https://esahubble.org/wordbank/gravitational-lensing/"
      },
      "tags": [
        "l13p3",
        "relativity",
        "lensing"
      ],
      "uid": "rtb8ot1l6zx95"
    },
    {
      "id": "ast-d-spacetime",
      "shape": "definition",
      "term": {
        "modality": "text",
        "value": "Spacetime"
      },
      "definition": {
        "modality": "text",
        "value": "The single geometry of space and time together, which mass and energy curve and which everything then travels through, gravity being the shape rather than a force"
      },
      "curatedDistractors": [
        "Redshift",
        "Parallax",
        "Lensing"
      ],
      "source": {
        "label": "NASA Imagine the Universe — Ask an Astrophysicist: relativity",
        "url": "https://imagine.gsfc.nasa.gov/ask_astro/relativity.html"
      },
      "tags": [
        "l13p3",
        "relativity",
        "spacetime"
      ],
      "uid": "btnct8rzdn1e"
    },
    {
      "id": "ast-q-light-deflection-cause",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Why is a beam of light deflected as it passes a massive object?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Gravity tugs on the photons"
        },
        {
          "modality": "text",
          "value": "The space it crosses is bent"
        },
        {
          "modality": "text",
          "value": "The light slows down and turns"
        },
        {
          "modality": "text",
          "value": "The photons have a tiny mass"
        }
      ],
      "correctIndex": 1,
      "explanation": "Photons have no mass, so nothing tugs on them and there is no tiny mass to weigh; nor does light slow and steer itself. Mass and energy curve spacetime, and light simply follows the curvature — which is the only reason a massless particle can be deflected.",
      "source": {
        "label": "NASA Imagine the Universe — Ask an Astrophysicist: relativity",
        "url": "https://imagine.gsfc.nasa.gov/ask_astro/relativity.html"
      },
      "tags": [
        "l13p3",
        "relativity",
        "spacetime"
      ],
      "uid": "z1n0cp1ubamat"
    },
    {
      "id": "ast-q-cosmological-redshift-cause",
      "shape": "mcqShort",
      "prompt": {
        "modality": "text",
        "value": "Why does light from a distant galaxy arrive stretched to longer wavelengths?"
      },
      "options": [
        {
          "modality": "text",
          "value": "An explosion flung it outward"
        },
        {
          "modality": "text",
          "value": "Space expanded in transit"
        },
        {
          "modality": "text",
          "value": "The galaxy races away from us"
        },
        {
          "modality": "text",
          "value": "We sit at the centre of it"
        }
      ],
      "correctIndex": 1,
      "explanation": "Astronomical redshifts are expansion redshifts: the space the light crossed grew while the light was crossing it. Galaxies are not debris racing outward from an explosion, and an observer on any galaxy sees the same thing — there is no centre and nothing to expand into.",
      "source": {
        "label": "ESA — What is 'red shift'?",
        "url": "https://www.esa.int/Science_Exploration/Space_Science/What_is_red_shift"
      },
      "tags": [
        "l13p3",
        "cosmology",
        "expansion"
      ],
      "uid": "14g94tinhcbbe"
    },
    {
      "id": "ot-cov-o7-1",
      "shape": "mcq",
      "prompt": {
        "modality": "text",
        "value": "About what fraction of Titan's thick atmosphere is nitrogen?"
      },
      "options": [
        {
          "modality": "text",
          "value": "About 40 percent"
        },
        {
          "modality": "text",
          "value": "About 95 percent"
        },
        {
          "modality": "text",
          "value": "About 60 percent"
        },
        {
          "modality": "text",
          "value": "About 10 percent"
        }
      ],
      "correctIndex": 1,
      "explanation": "Titan is the only moon with a substantial atmosphere, and it is about 95 percent nitrogen.",
      "tags": [
        "titan",
        "atmosphere"
      ],
      "uid": "fqlouq4fl3mo"
    },
    {
      "id": "ot-cov-o7-2",
      "shape": "mcq",
      "prompt": {
        "modality": "text",
        "value": "Which probe made the most distant landing ever achieved, touching down on Titan in January 2005?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Huygens"
        },
        {
          "modality": "text",
          "value": "Voyager 1"
        },
        {
          "modality": "text",
          "value": "Cassini"
        },
        {
          "modality": "text",
          "value": "Galileo"
        }
      ],
      "correctIndex": 0,
      "explanation": "ESA's Huygens probe landed on Titan on 14 January 2005, still the most distant landing achieved.",
      "tags": [
        "titan",
        "huygens"
      ],
      "uid": "d5wytc12ucxl6"
    },
    {
      "id": "ot-cov-o7-3",
      "shape": "mcq",
      "prompt": {
        "modality": "text",
        "value": "Why is Enceladus the most reflective body in the Solar System?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Plume material falls back and repaints the surface"
        },
        {
          "modality": "text",
          "value": "A thick ozone layer scatters incoming sunlight"
        },
        {
          "modality": "text",
          "value": "It has no craters to darken its surface"
        },
        {
          "modality": "text",
          "value": "Its interior ocean is visible through clear ice"
        }
      ],
      "correctIndex": 0,
      "explanation": "Most of Enceladus's vented plume falls back and repaints the surface, making it the Solar System's most reflective body.",
      "tags": [
        "enceladus",
        "plume"
      ],
      "uid": "13cz6zl9fgm79"
    },
    {
      "id": "ot-cov-o7-4",
      "shape": "mcq",
      "prompt": {
        "modality": "text",
        "value": "The material from Enceladus's plume that does not fall back to its surface mainly goes on to feed what?"
      },
      "options": [
        {
          "modality": "text",
          "value": "Saturn's Cassini Division"
        },
        {
          "modality": "text",
          "value": "Saturn's E ring"
        },
        {
          "modality": "text",
          "value": "Titan's atmosphere"
        },
        {
          "modality": "text",
          "value": "Saturn's magnetic field"
        }
      ],
      "correctIndex": 1,
      "explanation": "Enceladus is the moon building Saturn's faint E ring from its escaping plume material.",
      "tags": [
        "enceladus",
        "rings"
      ],
      "uid": "1da8acpr0cnh1"
    }
  ]
}