Gaia (ESA astrometric survey)

node · earth · Sun-Earth L2, then heliocentric orbit

The European Space Agency astrometric observatory that measured positions, parallaxes and proper motions for nearly two billion sources, converting the Hertzsprung-Russell diagram from a schematic into a measured distribution and pinning down distances - and therefore luminosities, radii and ages - across the Galaxy. Its science observations ended on 15 January 2025 after about twelve years, and the spacecraft was passivated and moved to a heliocentric retirement orbit on 27 March 2025. The data releases lag the observations by years: Data Release 3 appeared in 2022, Data Release 4 is planned for December 2026 and is described by ESA as the first release covering all data types for the full nominal five and a half year mission, and the final legacy catalogue is not expected before the end of the decade. The mission is therefore over while its principal scientific output is still ahead of it. Not a place on Earth.