Stars bright-star subset — data attribution and scope

Source: HYG v4.1, David Nash / Astronexus.
https://github.com/astronexus/HYG-Database/tree/main/hyg
Current upstream project: https://codeberg.org/astronexus/hyg
Source file: https://raw.githubusercontent.com/astronexus/HYG-Database/main/hyg/CURRENT/hygdata_v41.csv
Retrieved 2026-11-01.
License: Creative Commons Attribution-ShareAlike 4.0 International.
https://creativecommons.org/licenses/by-sa/4.0/
This adapted data subset remains under CC BY-SA 4.0.
Changes: exclude the Sun; select visual magnitude <= 5.5; retain eight fields;
convert RA from hours to degrees; round RA/Dec to 6 decimals; serialize JSON.
Fields: [HYG id, RA degrees J2000, Dec degrees J2000, visual magnitude,
B-V color index or null, proper name, mu_alpha*cos(dec) mas/year, mu_delta mas/year].
The original catalogs include Hipparcos, Yale Bright Star and Gliese.
Only the data is adapted. No Stellarium code, graphics or engine is used.

Model: tangent-vector proper motion from epoch J2000, IAU 1976 precession
polynomials to mean equator/equinox of date, approximate Greenwich mean
sidereal time from UTC, and geometric altitude/azimuth at a manual location.
Projection: azimuthal equidistant, centred on zenith, north up and east left.
Geometric horizon only; below-horizon stars are hidden. Mobile limit: mag <=5.
Default Greenwich coordinates are an explicit example, NOT inferred location.
Intended period: 2000–2050. UTC is used as an approximation for UT1 and TT.
No nutation, aberration, parallax, radial-motion correction, atmospheric
refraction, extinction, daylight, planets, Sun, Moon or weather simulation.
Do not use as an accurate instrument pointing or navigation solution.
A daytime chart can display stars that are not visible to the naked eye.

Formula background (independent implementation):
https://aa.usno.navy.mil/faq/GAST
https://aa.usno.navy.mil/faq/alt_az
Lieske et al. (1977), IAU 1976 precession; compact J2000 polynomial form.

Original upstream license declaration: /hyg-LICENSE.txt
Original upstream field/attribution notes: /hyg-source-readme.txt
Original CSV SHA256: d9f69fd86bbf90a4e4d52b4c5c53eacfa6dfc0bfdef85bfd94f095e0bebe4ebd
Subset SHA256: bb4ee7b5f51b7fb9ed1e52d881764515da403a16940d7ba8676d10275be51ba6
