The Gaia satellite turns on its axis and around the Earth, peering through its two telescopes. Using its 106 detectors, which constitute the equivalent of a camera with a resolution of a billion pixels, it thus observes daily 50 milion stars , with ten measurements at each passage, which represents a total of 500 million picture elements per day. This gigantic amount of data has led to the publication of a catalogue for the positions in the sky of 1,15 billion stars. The accuracy is from 0,5 to 15 thousandths of a second of arc : not that a second of arc corresponds to the angle subtended by a 1 euro coin at a distance of 4 000 km.
With 200 million more stars than originally foreseen, this catalogue will enable scientists to accumulate a statistic which could not have been done without such a huge data base. Included is data for 250 000 quasars and 3 000 Cepheid and RR Lyrae variable stars. The Gaia mission has has produced the light curves of these latter stars, i.e. the time variation of their brightness, in order to better understand the physical phenomena which govern these variable stars.
The positions of 2 million of these stars have also been compared with measurements made 23 years earlier by ESA’s Hiparcos mission. The differences enable one to calculate the speed and distance of these stars with respect to the solar system The accumulation of the information in this catalogue stopped in September 2015 but, since Gaia is still accumulating data, the scientists hope to be able to compare in
the same way the future positions of the stars with those given here. They hope thus to obtain towards the end of 2017, the speeds and velocities of this set of a billion stars.
French institutions play a major role in this mission, and include over one hundred scientists, engineers and technicians, within the consortium. They participate in numerous projects vital to the success of this mission : organization of the ground based observations required for the data processing, preparation of the ephemeris of the solar system, daily optical observation of the Gaia satellite itself, (in order to know its exact position and speed with the highest possible accuracy), validation of the data processing, etc.
The laboratories involved are :
- Le Laboratoire Galaxies, étoiles, physique et instrumentation (Observatoire de Paris/CNRS/Université Paris Diderot)
- Le Laboratoire Systèmes de référence temps-espace (Observatoire de Paris/CNRS/UPMC)
- Le Laboratoire d’études du rayonnement et de la matière en astrophysique et atmosphères (Observatoire de Paris/CNRS/ENS Paris/UPMC/Université de Cergy-Pontoise)
- L’Institut de mécanique céleste et de calcul des éphémérides (Observatoire de Paris/CNRS/UPMC/Université Lille 1)
- Le Laboratoire Lagrange (CNRS/Observatoire de la Côte d’Azur/Université de Nice Sophia Antipolis)
- Le Laboratoire d’astrophysique de Bordeaux (CNRS/Université de Bordeaux)
- L’Observatoire astronomique de Strasbourg (CNRS/Université de Strasbourg)
- Le Laboratoire Univers, transport, interfaces, nanostructures, atmosphère et environnement, molécules (CNRS/Université de Franche-Comté)
- Le Laboratoire univers et particules de Montpellier (CNRS/Université Montpellier)
The on-line resources of the Centre de données astronomiques de
Strasbourg (CNRS/Université de Strasbourg) have also play an important
role in the validation of the data and are indispensable for the
scientific analysis.
The CNES is a key actor with the french teams, thanks to the
establishment of the DPAC data processing centre eat Toulous (which is
responsible for about 40 % of the data processing). The DPAC was
confirmed in 2006 for the data handling of the Gaia satellite, and six
specialized computer centres such as the one at Toulouse, have been
signed up for this purpose.