Gaia’s telescopes, with their ten mirrors, focus and direct light onto Gaia’s three science instruments, which are housed inside a protective dome within the payload module.
The astrometric instrument (ASTRO)
Gaia’s main astrometric instrument precisely determines the positions of stars in the sky. By combining the measurements of any given star over the five-year mission, it will be possible to determine its parallax (and therefore its distance) and its proper motion (the velocity of the star as it moves on the plane of the sky).
The radial velocity spectrometer (RVS)
The RVS reveals the velocity of the star along the line of sight of Gaia by measuring the Doppler shift of absorption lines in a high-resolution spectrum.
The photometric instrument (BP/RP)
The photometric instrument provides colour information by generating two low-resolution spectra in red and blue. This allows astronomers to determine key stellar characteristics such as temperature, mass and chemical composition.