GAIA: An Astrometric and Photometric Survey of our Galaxy

In October 2000, the GAIA astrometric mission was approved as one of the next two `cornerstones' of ESA's science programme, with a launch date target of 2010–12. GAIA will provide positional, radial velocity, and photometric measurements with the accuracies needed to produce a stereoscopic and kinematic census of about one billion stars throughout our Galaxy (and into the Local Group), amounting to about 1 per cent of the Galactic stellar population. GAIA's main scientific goal is to clarify the origin and history of our Galaxy, from a quantitative census of the stellar populations. It will advance questions such as when the stars in our Galaxy formed, when and how it was assembled, and its distribution of dark matter. The survey aims for completeness toV =20 mag, with accuracies of 10 μas at 15 mag. This revised version was published online in July 2006 with corrections to the Cover Date.