# Milky Way backdrop — Gaia EDR3 all-sky colour map

`data/milky_way_gaia_edr3.jpg` is an adaptation of

> **The colour of the sky from Gaia's Early Data Release 3 – equirectangular projection**
> Copyright: **ESA/Gaia/DPAC**; CC BY-SA 3.0 IGO. Acknowledgement: A. Moitinho.
> <https://sci.esa.int/web/gaia/-/the-colour-of-the-sky-from-gaia-s-early-data-release-3-equirectangular-projection>

Source file: `Gaia_EDR3_flux_cartesian_4k.png` (4000 × 2000, galactic
coordinates, galactic centre in the middle, longitude increasing to the left).

Changes made for Expanse: resampled to 4096 × 2048 (Lanczos) and saved as
JPEG (quality 85). At runtime the game darkens, re-contrasts and slightly
tints it in `shaders/milky_way_sky.gdshader`, and rotates it from galactic to
equatorial coordinates (IAU J2000 matrix, `scripts/sky_backdrop.gd`).

This adapted image is licensed under the
[Creative Commons Attribution-ShareAlike 3.0 IGO License](https://creativecommons.org/licenses/by-sa/3.0/igo/),
the same licence as the original. It is not covered by the MIT licence of the
game code. ESA does not endorse Expanse.