# Credits and data sources

CycleCalcs is built on open astronomy libraries and data.

- **Astronomy Engine** (MIT License, by Don Cross) is vendored as
  `assets/vendor/astronomy.browser.min.js` and powers every live calculation in
  the browser: Sun, Moon and planet positions, phases, conjunctions, eclipses
  and seasons. https://github.com/cosinekitty/astronomy

- **Yale Bright Star Catalog** (Hoffleit and Warren 1991) and the
  **SAO Star Catalog** (SAO Staff 1966), both served by NASA HEASARC, are used
  at build time only, never redistributed in raw form. They provide the
  naked-eye star positions in `assets/data/sky-stars.json`, the depth tier in
  `assets/data/sky-stars-deep.json` and the per-constellation metadata in
  `assets/data/constellations.json`. Neither asserts a usage restriction; see
  NOTICE.md PART 2.1, which also records the ESA Hipparcos dependency these
  replaced and why it was removed.

- **GeoNames** (CC BY 4.0, https://www.geonames.org/) provides the place index
  in `assets/data/cities-top.txt` and `assets/data/cities-rest.txt`, built by
  `tools/generate-cities.mjs` from the cities5000 export. It is what lets a
  city search and a "use my location" place name be answered inside the
  reader's browser, so neither their coordinates nor the text they type is
  ever sent to an outside service.

- **NOAA Space Weather Prediction Center** (a US Government work, public
  domain) provides the yearly mean sunspot numbers plotted on the sunspot
  cycle page, taken from the observed solar cycle indices.
  https://www.swpc.noaa.gov/products/solar-cycle-progression

- **d3-celestial constellation figure lines and deep-sky catalogs**
  (BSD-3-Clause, Copyright Olaf Frohn). The connect-the-dots figures in
  `assets/data/constellation-lines.json` and the base Messier/Caldwell object
  data behind `assets/data/messier.json` and the Messier Catalog page are
  derived from these datasets, which in turn trace to the SAC Deep Sky
  Database. https://github.com/ofrohn/d3-celestial

- **Wikipedia, "List of Messier objects"** (text CC BY-SA; the underlying
  astronomical measurements are uncopyrightable facts). Used at build time as
  the cross-validation source for the Messier page's distances, NGC ids and
  common names; every value is checked against the site's own catalog and the
  IAU constellation boundaries before it ships.

- **IAU Catalog of Star Names** (IAU Working Group on Star Names, WGSN;
  IAU data, CC BY 4.0). The official proper names, meanings and origins in
  `tools/star-names-wgsn.json` and on the Star Names page are the WGSN's,
  as published in its live catalog. https://exopla.net/star-names/modern-iau-star-names/

- **Meteor shower working-list values** (International Meteor Organization,
  imo.net, cross-checked against the American Meteor Society calendar). The
  peak solar longitudes, radiants, drifts, ZHRs and speeds in
  `assets/js/meteors.js` / `tools/meteor-catalog.mjs` follow the IMO's
  published working list; peak instants are computed from those longitudes.

Constellation boundaries, names and the traditional figures follow the
International Astronomical Union (IAU).