docs/library-content.org

{
  "id": "mars",
  "section": "planets",
  "title": "Mars",
  "subtitle": "Fourth planet from the Sun",
  "facts": [
    { "label": "Mean distance from the Sun", "value": "1.524 AU (227.9 million km)", "source": 0 }
  ],
  "essay": "Plain text, paragraphs separated by a blank line.",
  "image": {
    "url": "https://… direct .jpg or .png",
    "credit": "NASA/JPL-Caltech",
    "licence": "Public domain",
    "page": "https://… page the image is published on",
    "caption": "One sentence on what the image shows."
  },
  "drawing": { "kind": "planet", "radiusKm": 3389.5, "rings": false, "axialTiltDeg": 25.19, "color": "#C1440E" },
  "link": { "body": "mars" },
  "sources": [
    { "title": "NASA Mars Fact Sheet", "url": "https://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html" }
  ]
}

• id: lowercase, hyphenated, unique across all sections (e.g. m42, ori, sirius, voyager-1).
• section: one of sun, planets, dwarf-planets, moons, constellations, stars, deep-sky, missions, exoplanets, rockets.
• facts: 4–8 items. Every fact has source, an index into sources. Units in SI or AU, with conversions where helpful. Use tabular style: "10 h 33 m", "29.4 Earth years".
• sources: 1–5 items, primary or authoritative (NASA NSSDC fact sheets, NASA science pages, JPL, IAU, ESA, NOIRLab, SIMBAD). Every URL must return HTTP 200 when checked.
• image: optional only for constellations, stars, missions and rockets when no verifiable image exists (set to null).

• drawing: per section:

  • planets, dwarf planets, moons, sun: {"kind": "planet", "radiusKm", "rings", "axialTiltDeg", "color"}; color is a representative hex.
  • constellations: {"kind": "constellation"} (the app draws the figure from its line data).
  • stars: {"kind": "star", "spectralType": "A1V", "colorIndex": 0.0} (B−V).
  • deep sky: {"kind": "deep-sky", "type": "galaxy|globular|open|nebula|planetary|supernova-remnant", "sizeArcmin": 90}.
  • missions: {"kind": "mission", "status": "active|complete|lost", "launch": "1977-09-05"}.
  • exoplanets: {"kind": "exoplanet", "radiusEarth": 1.07, "orbitAU": 0.0485, "starTempK": 2566} (omit a field if no measured value).
  • rockets: {"kind": "rocket", "heightM": 70.0, "diameterM": 3.7, "status": "active|retired|in development"}.
• link: what the page describes in the rest of the app: {"body": "mars"}, {"constellation": "Ori"} (IAU abbreviation), {"hr": 2491} (Bright Star Catalogue number), {"messier": 42}, {"spacecraft": "Voyager 1"}, or {}.

• 150–250 words, two or three short paragraphs.
• Plain, direct English, as a knowledgeable colleague would write. No hype, no dramatic framing, no rhetorical questions, no "fascinating", "stunning", "mysterious", "breathtaking".
• Concrete facts over adjectives: what it is, how we know, one or two things that make it distinctive, and for observable objects how to find it or what it looks like to the eye or a small telescope.
• Original wording. Draw on public-domain NASA/JPL text and on facts from other sources, but never copy sentences from Wikipedia (CC BY-SA) or any copyrighted text.
• Present tense for current facts; dates as "1977", "2034".

Allowed, in order of preference:

1. NASA (images-api.nasa.gov, images-assets.nasa.gov, science.nasa.gov, photojournal.jpl.nasa.gov): licence: "Public domain". Skip images whose NASA page credits a third party or says they are copyrighted.
2. ESA/Hubble (esahubble.org), ESA/Webb (esawebb.org), NOIRLab (noirlab.edu), ESO (eso.org): licence: "CC BY 4.0", credit copied exactly from the image page. No images showing identifiable people.
3. Historical star atlas plates in the public domain (Library of Congress, Linda Hall Library) for constellations: licence: "Public domain".

Use a direct file URL of a moderate size (roughly 800–2000 px; NASA ~medium.jpg or ~large.jpg, ESA "large"/"screen" sizes). Check every image URL with curl -sI and keep only HTTP 200 with an image content type.

• Invent values. If a fact cannot be sourced, leave it out.
• Use Wikipedia as a sources entry.
• Touch any file other than your own section file. No git commands.