Gaia: the European observatory that mapped two billion objects in the Milky Way

Background

Catalogues of stellar distances and motions used by astronomers around the world rest on Gaia, a European Space Agency mission whose status ESA now lists as post-operations. ESA describes Gaia as a global space astrometry mission that built the largest, most precise three-dimensional map of our Galaxy by surveying nearly two billion objects. From 27 July 2014 to 15 January 2025, Gaia made more than three trillion observations of two billion stars and other objects throughout the Milky Way galaxy and beyond, mapping their motions, luminosity, temperature and composition. Through the mission Gaia monitored each of its target stars about 14 times per year, charting their positions, distances, movements and changes in brightness. It studied more than 1 million distant quasars and provided stringent new tests of Albert Einstein's General Theory of Relativity. Gaia's data are used to identify which stars are relics of smaller galaxies long ago swallowed by the Milky Way.