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Gaia is a European Space Agency (ESA) space observatory currently mapping stars and other astronomical objects carrying out astrometry along with some photometry and spectrography. As per design, it has mapped and is tracking over a billion stars. It has two 1.45 × 0.5 meter telescopes viewing the optical to very near infrared range. It is deployed at the L2 Earth-Sun Lagrangian point. It was launched in 2013 for a five year primary mission, extended into 2025 when its fuel is estimated to run out, and processing of its data is expected to continue to 2030. Instruments:
Its resulting catalog has been released as Gaia Data Release 1 (Gaia DR1) in 2016, Gaia Data Release 2 (Gaia DR2) in 2018, Gaia Early Data Release 3 (Gaia EDR3) in 2020, and Gaia Data Release 3 (Gaia DR3) in 2022. Data includes coordinates over time, yielding parallax distances and proper motion, useful, e.g., for identifying stellar associations, and for determining mass when visual binaries are resolved.
The Gaia-ESO Survey (GES) is a survey conducted with Gaia and European Southern Observatory Very Large Telescope (ESO VLT) of 100,000 stars within four open clusters, using Gaia astrometric data along with spectroscopy using a VLT multi-object spectrograph.
Gaia's instruments slightly polarize the light, which must be taken into account in interpreting its astrometry. This also creates the opportunity to extract some polarization data for Gaia's billion-plus target stars by reverse-engineering the effects of the instruments on received polarized light.
In addition to the astrometry of stars, Gaia data includes observations of solar system bodies, and makes a considerable contribution to working out their orbits.
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