Le premier ciel de Gaia

Abstract

On 14 September 2016, the first data release of the ESA's Gaia mission has been published. Based on raw data collected between 25 July 2014 and 16 Septembre 2015, i.e. only over the first 14 months of mission, this first "Gaia sky" includes the accurate positions and Gaia magnitudes of more than a billion objects: it is already the largest all-sky survey to date even though the incomplete scanning of some areas of the sky is reflected by some artefacts that will gradually fade out as more data are collected. In addition, for a subset of two million stars in common between Gaia and the Hipparcos and Tycho-2 catalogues, positions, parallaxes and proper motions have been obtained with an accuracy 3 times better than those of Hipparcos and for 20 times more stars. Finally, light curves of about 3200 RR Lyrae and Cepheid variable stars have been obtained from the repeated observations of the Ecliptic Poles made during the first month of Gaia operations. A first glance at the quality of the data is presented here, as well as some remarks about the use of this very preliminary Gaia catalogue.