Lecture at the José Cabanis Media Library of Toulouse on 26 February 2019.
by François Mignard,astronomer, director of research at CNRS.
Summary: On 25 April 2018, ESA and the European Consortium DPAC delivered the second version of the results produced by the observations of the Gaia satellite. By the diversity and volume of data, and especially the extreme precision of astrometry and photometry, an important date in the history of astronomy was thus written. The history of the Milky Way is at the centre of this space mission and I will explain why astronomers have worked so hard for more than two centuries to track down stellar distances and the reasons that have caused the European space sector to want to do so for a billion stars in our galaxy.