Data sources & credits
Last updated: July 26, 2026
Stargaze Tonight is built on openly licensed astronomical data. This page carries the attributions those licences require, in full.
Star catalogue
HYG Database v4.2 — a merge of the Hipparcos, Yale Bright Star and Gliese catalogues, compiled by David Nash / Astronexus. Licensed CC BY-SA 4.0. Source: codeberg.org/astronexus/hyg.
The app ships a subset of this catalogue (stars brighter than magnitude 5.5) reprojected and re-encoded for on-device use.
Share-alike: our derived dataset
Because HYG is CC BY-SA 4.0, the share-alike clause requires that our processed version of it be published under the same licence. It is released as CC BY-SA 4.0 at github.com/DevJihwan/stargaze-tonight-star-catalog (publication pending — the link will appear here when the repository goes public.)
That release contains the filtered and re-encoded star table used by the app, plus the script that produces it from the upstream HYG files, so anyone can reproduce or reuse it.
Constellations
Constellation boundaries follow the IAU 88 constellation boundaries established by Eugène Delporte (1930), which are effectively public domain.
Constellation charts and naming follow the IAU reference set: “IAU / Sky & Telescope (Roger Sinnott & Rick Fienberg)”, licensed CC BY 4.0. Source: iau.org/public/themes/constellations.
Constellation stick figures are drawn by us. Stellarium’s sky cultures are GPL-licensed and were deliberately not used.
Weather
Cloud cover and hourly weather come from Apple Weather (Apple WeatherKit). See Apple’s legal attribution page and its data source list.
Astronomical algorithms
Positions of the sun, moon and planets, rise and set times, twilight and lunar phases are computed from the algorithms in Jean Meeus, Astronomical Algorithms, 2nd ed. (Willmann-Bell, 1998) — VSOP87D for the Earth, an abridged ELP2000-82 for the moon, and JPL’s approximate Keplerian elements for the planets. The implementation is our own.
The engine is validated against published ephemerides — U.S. Naval Observatory rise/set/twilight times and JPL Horizons positions — before every release.
What we deliberately did not use
The World Atlas of Artificial Night Sky Brightness (2015) is licensed CC BY-NC, which forbids commercial use. Because this app carries advertising, that dataset is off limits, so the app has no light-pollution map and no feature that depends on one. We would rather ship less than infringe.
Legal
Get tonight’s answer on your phone
Stargaze Tonight rates tonight’s observing conditions where you are, shows an hour-by-hour darkness strip, and tells you what is actually worth looking at. Free, ad-supported, no subscription.
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