Gaia probe

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Gaia is an astrometry space mission, and a successor to the ESA Hipparcos mission. It was included within the context of the ESA Horizon 2000 Plus long-term scientific programme in 2000. It is expected to be launched by the ESA in the second half of 2011, and will be operated in a Lissajous-type orbit around at the second Lagrangian point (L₂) of the Sun-Earth-Moon system.

Gaia will compile a catalogue of approximately one billion stars to magnitude 20. Its objectives comprise (a) astrometric (or positional) measurements, determining the positions, distances, and annual proper motions of stars with an accuracy of about 20 µas (microarcsecond) at 15 mag, and 200 µas at 20 mag; (b) photometric measurements, providing multi-colour multi-epoch observations of each detected object; and (c) radial velocity measurements. Gaia will create an extremely precise three-dimensional map of stars throughout our Milky Way galaxy and beyond, and map their motions which encode the origin and subsequent evolution of the Milky Way. The photometric measurements will provide the detailed physical properties of each star observed, characterising their luminosity, temperature, gravity, and elemental composition. This massive stellar census will provide the basic observational data to tackle a wide range of important problems related to the origin, structure, and evolutionary history of our Galaxy. Large numbers of quasars, galaxies, extrasolar planets, and solar system bodies will be measured at the same time.