From an ESA press release, September 14, 2016 :
The first catalogue of more than a billion stars from ESA’s Gaia satellite was published on September 14, 2016 – the largest all-sky survey of celestial objects to date.
On its way to assembling the most detailed 3D map ever made of our Milky Way galaxy, Gaia has pinned down the precise position on the sky and the brightness of 1.142 billion stars. As a taster of the richer catalogue to come in the near future, this data release also features the distances and the motions across the sky for more than two million stars.
The map projection above shows an all-sky view of stars in the Milky Way and our neighboring galaxies, based on the first year or so of Gaia’s observations. It shows the density of stars observed by Gaia in each portion of the sky. Brighter regions indicate denser concentrations of stars, while darker regions correspond to patches of the sky where fewer stars are observed. Darker regions across the Galactic Plane correspond to dense clouds of interstellar gas and dust that absorb starlight along the line of sight. Many globular and open clusters – groupings of stars held together by their mutual gravity – are also sprinkled across the image.
Note that the faint curved features and dark stripes are not of astronomical origin but rather reflect Gaia’s scanning procedure. As this map is based on observations performed during the mission’s first year, the survey is not yet uniform across the sky. These artefacts will gradually disappear as more data are gathered during the five-year mission.