Gaia

Gaia was a European Space Agency (ESA) space observatory that mapped stars and other astronomical objects carrying out astrometry along with some photometry and spectrography. As per design, it mapped and tracked over a billion stars. It had two 1.45 × 0.5-meter telescopes viewing the optical to very near infrared range. It was deployed at the L2 Earth-Sun Lagrangian point. It was launched in 2013 for a five year primary mission, which was extended, observation continuing until January 2025. Data-downloads and navigation into a heliocentric orbit (freeing L2 of its presence) were completed in March 2025, at which time the spacecraft was deactivated. Processing of its data is expected to continue until at least 2030. Instruments:

• Astro - astrometry instrument (aka Gaia G, observations termed G band).
• BP/RP - blue photometer/red photometer (aka G_BP and G_RP).
• RVS - radial-velocity spectrometer (aka G_RVS).

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. Planned future releases include Gaia DR4, including all the primary mission data, and Gaia DR5, a final release including the entire mission's data. 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 polarized 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.