# Gaia DR3 data licence — `data/gaia_stars.bin`

`data/gaia_stars.bin` is derived from the **Gaia Data Release 3** catalogue
(`gaiadr3.gaia_source`) of the European Space Agency (ESA) mission *Gaia*,
retrieved from the ESA Gaia Archive (https://gea.esac.esa.int/archive/) by
`tools/fetch_gaia.py`.

**Credit: ESA/Gaia/DPAC.**

> This work has made use of data from the European Space Agency (ESA) mission
> Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing
> and Analysis Consortium (DPAC,
> https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC
> has been provided by national institutions, in particular the institutions
> participating in the Gaia Multilateral Agreement.

Reference: Gaia Collaboration, Vallenari, A., et al. (2023), *Gaia Data Release
3: Summary of the content and survey properties*, A&A 674, A1.

## Licence

Per https://www.cosmos.esa.int/web/gaia-users/license (checked 2026-09-26):
"Gaia data are distributed under the **CC BY-NC 3.0 IGO** license. For details
and guidelines concerning commercial use of the Gaia data, please see the Terms
and Conditions for the use of data in the ESA space science archives."

Licence text: https://creativecommons.org/licenses/by-nc/3.0/igo/

Note the **NonCommercial** term: Expanse is a free, MIT-licensed game, which is
fine. Any commercial distribution of this file (or of a build that contains it)
needs ESA's permission under the archive's Terms and Conditions — or drop the
file; the game falls back to the HYG catalog alone when it is missing.

## What was changed

Selected rows and columns only (source_id, ra, dec, parallax,
phot_g_mean_mag, bp_rp); converted to heliocentric positions in light-years
(distance = 1/parallax), absolute G magnitude (0.25 mag steps) and a B−V-like
colour index derived from BP−RP (16 steps), packed as float16. Stars matched to
the HYG catalog (`data/stars.csv`) or listed in `data/stars_extra.csv` (the
exoplanet hosts HYG lacks, by Gaia DR3 source_id) are flagged. See `tools/fetch_gaia.py` for
the exact query and conversions.