Gaia Data Release 1: Astrometry - one billion positions, two million proper motions and parallaxes

Understand

Gaia Data Release 1 (Gaia DR1) contains astrometric results for more than 1 billion stars brighter than magnitude 20.7 based on observations collected by the Gaia satellite during the first 14 months of its operational phase.

• We give a brief overview of the astrometric content of the data release and of the model assumptions, data processing, and validation of the results.
• For stars in common with the Hipparcos and Tycho-2 catalogues, complete astrometric single-star solutions are obtained by incorporating positional information from the earlier catalogues.
• For other stars only their positions are obtained by neglecting their proper motions and parallaxes.