{
  "page": "One Light-Day, https://onelightday.vercel.app/",
  "independence": "Independent work. NASA, JPL and Caltech appear here as sources of data and of one quoted statement; none of them has reviewed or endorsed this page.",
  "sources": [
    {
      "name": "JPL Horizons API",
      "publisher": "NASA/JPL-Caltech Solar System Dynamics",
      "url": "https://ssd.jpl.nasa.gov/api/horizons.api",
      "retrieved": "2026-10-08",
      "licence": "NASA/JPL data, U.S. government work; Horizons asks that it be credited as the source.",
      "used_for": [
        "public/hourly.json: Voyager 1 (COMMAND '-31'), CENTER '500@399', OBSERVER table, QUANTITIES '20,21', EXTRA_PREC YES, hourly 2026-01-01 to 2029-01-01 UTC; the one-way down-leg light time (quantity 21) stored in microseconds.",
        "public/mission.json: the same observer table every day 1977-09-06 to 2099-12-31 (Horizons' trajectory ends 2099-12-31 23:58:50 UT); range kept every fifth day in thousands of km.",
        "public/vectors.json: VECTORS, CENTER '500@0' (solar-system barycentre), VEC_TABLE 2, REF_PLANE FRAME (ICRF), TDB, daily 2026-01-01 to 2029-01-01 for Voyager 1 (-31) and the Earth (399).",
        "test/fixtures: hourly vectors, 30 random minutes, light-time from Goldstone, Canberra and Madrid (SITE_COORD), and light-time seen from Voyager 1 (CENTER '500@-31'), each fetched for the receipts and never used by the page."
      ],
      "trajectory": "Voyager_1_ST+refit2022_m: JPL's 2022 refit of the tracking that ended in 1992, carried forward. Every distance on this page is that prediction."
    },
    {
      "name": "Where are Voyager 1 and Voyager 2 now?",
      "publisher": "NASA",
      "url": "https://science.nasa.gov/mission/voyager/where-are-voyager-1-and-voyager-2-now/",
      "retrieved": "2026-10-08",
      "quoted": "On Wednesday, Nov. 18, 2026, at 2:16:07 a.m. PST, NASA’s Voyager 1 spacecraft will be 16.094 billion miles (25.902 billion kilometers) away from Earth — or, the distance light travels in 24 hours, also known as one light-day.",
      "reading": "2:16:07 a.m. PST is 10:16:07 UTC. The statement does not name its observer or its definition of distance; solved as the distance from the centre of the Earth with both bodies taken at one instant, Horizons' vectors give 10:16:06.996 UTC (test/receipts.test.ts)."
    },
    {
      "name": "Press conversions of NASA's moment (checked, not used)",
      "notes": [
        "EarthSky, Kelly Kizer Whitt, 26 June 2026, https://earthsky.org/space/voyager-1-1-light-day-from-earth-november-17-18-2026/ gives 12:16:07 a.m. CST, which is 06:16:07 UTC. NASA's 2:16:07 a.m. PST is 4:16:07 a.m. CST; the press figure is a conversion error by two hours, and this page does not use it.",
        "IFLScience, Alfredo Carpineti, 19 June 2026, https://www.iflscience.com/its-official-voyager-1-will-cross-the-1-light-day-threshold-on-november-18-2026-82733 gives 2:16:07 a.m. PST, matching NASA."
      ]
    },
    {
      "name": "DSN Telecommunications Link Design Handbook 810-005, module 301 (coverage and geometry)",
      "publisher": "NASA/JPL-Caltech",
      "url": "https://deepspace.jpl.nasa.gov/dsndocs/810-005/",
      "used_for": "Geodetic positions and heights of DSS-14 Goldstone, DSS-43 Canberra and DSS-63 Madrid (src/places.ts); the receipts use the same coordinates through Horizons' SITE_COORD."
    },
    {
      "name": "GeoNames cities1000",
      "publisher": "GeoNames",
      "url": "https://www.geonames.org/",
      "licence": "CC BY 4.0",
      "used_for": "src/data/cities.json: 92 cities with coordinates, heights and IANA zones, copied from github.com/MeeshaBear1/besselian."
    },
    {
      "name": "Almucantar engine: angles, time, sidereal time, precession and nutation",
      "url": "https://github.com/MeeshaBear1/almucantar",
      "licence": "MIT",
      "used_for": "src/engine/astro/*.ts copied unchanged (commit 1f49f28); rotation and precession/nutation matrices in src/engine/site.ts, after J. Meeus, Astronomical Algorithms, 2nd ed., 1998."
    },
    {
      "name": "Besselian and Gnomonics",
      "url": ["https://github.com/MeeshaBear1/besselian", "https://github.com/MeeshaBear1/gnomonics"],
      "licence": "MIT",
      "used_for": "Adapted: place handling, time formatting, the service worker, the icon script and the smoke test (Besselian); type-as-outlines for the poster (Gnomonics)."
    },
    {
      "name": "Typefaces",
      "used_for": "Martian Mono (Evil Martians) and Literata (TypeTogether), both SIL Open Font License 1.1, self-hosted from the @fontsource packages; the poster's type is drawn as outlines from the same files with opentype.js (MIT)."
    }
  ],
  "methods": {
    "time": "UTC throughout; TDB = UTC + 69.184 s (37 leap seconds + 32.184 s), with no leap second assumed before 2029, as Horizons assumes. UT1 is taken as UTC for the Earth's rotation (under 0.1 s, under 0.1 mm of light-time).",
    "light_time": "Down-leg: the light reaching the observer at t left Voyager 1 at t − τ, solving |V(t − τ) − O(t)| = cτ by four fixed-point passes. Up-leg and reply legs solved the same way. A place's light-time is Horizons' geocentric value plus the vectors' difference between the place and the centre of the Earth.",
    "interpolation": "Cubic Hermite on the hourly light-time with slopes from centred differences of the table (Horizons' range-rate column is the instantaneous radial velocity and was 2 m/s away from the slope the table needs); cubic Hermite with Horizons' own velocities on the daily vectors.",
    "crossings": "Scanned at one hour (ten minutes for a place) and bisected to a millisecond.",
    "receipts": "test/receipts.test.ts: tolerances fixed in one object at the top before the first comparison and never loosened. The light-time crossing against NASA's moment is a named expected failure: a different definition, 57,680 s apart."
  }
}