A → European Space Agency → astrometry mission launched on 19 December 2013. Gaia's goal is to create the largest and most precise three-dimensional chart of the → Milky Way galaxy by providing unprecedented positional (position on the sky and distance to the Sun) and annual → proper motion measurements for about one billion stars in our Galaxy and throughout the → Local Group. Moreover, the third component of the velocity, the → radial velocity, will be obtained for all stars down to V = 17 mag. Similarly, multi-color photometry will be carried out on all stars down to V = 20 mag. Gaia will achieve the planned astrometric requirements by repeatedly measuring the positions of all objects down to V = 20 mag with final accuracies of about 20 microarcsec at 15 mag. It will provide distances accurate to 20% as far as the → Galactic Center. The satellite is expected to be launched in 2012 and be placed in a → Lissajous orbit around the Sun-Earth → Lagrangian point L2. Gaia is a much more advanced version of the → Hipparcos mission.
Initially, GAIA was the short for Global Astrometric Interferometer for Astrophysics. Although subsequently the interferometer option was abandoned, the acronym was maintained in lower case.