Gaia - The discovery machine 
 
 Gaia will make a very precise 3D map of our Milky Way Galaxy 
 
 It is the successor to the Hipparcos satellite which mapped some 100,000 stars 
 
 The one billion to be catalogued by Gaia is still only 1% of the Milky Way's total 
 
 But the survey's quality promises a raft of discoveries beyond just the star map 
 
 It will find new asteroids and planets; It will test physical constants and theories 
 
 Gaia's sky map will be the reference to guide future telescopes' observations 
 
 By repeatedly viewing its targets over five years, it should get to know the brightest stars' coordinates down to an error of just seven micro-arcseconds. Its goal is to make the largest, most precise map of where Earth dwells by observing the position of each of these stars 70 times over five years. This can help reveal details of their chemical makeup as well as its temperature, as the color of a star depends on its surface temperature. All in all, Gaia will help shed light on the composition, formation and evolution of the stars that make up the galaxy, researchers say. All in all, Gaia can measure the distances of stars as far away as the galactic center — roughly 32,500 light-years away — with an accuracy within 10 percent. (An astronomical unit is equal to Earth's distance from the sun — about 93 million miles, or 150 million kilometers.)
– While you were sleeping, a truly massive undertaking got under way, one that the BBC terms "one of the most ambitious space missions in history." Europe's Gaia satellite—which has been two decades in the making—launched at 4:12am EST today, setting it on a course to essentially inventory the Milky Way and create a 3D map of it, reports Space.com. The satellite will be tasked with logging the positions and distances to some 1 billion stars—that's 1% of the stars in the galaxy—but it's expected to turn up much more. Its sophisticated instruments (among them, a 1 billion-pixel camera) should facilitate the discovery of unknown asteroids, comets, dead stars, and even planets, reports the BBC. The end result: The most realistic understanding yet of how the Milky Way was assembled. The European Space Agency describes the process: Each star will be reviewed an average 70 times over a five-year period, with Gaia measuring the distance of the star from the sun (along with properties like brightness, temperature, and chemical composition) as it moves around the sun. The repeat measurements will allow Gaia to map the brightest stars' coordinates to within seven micro-arcseconds, which an ESA official describes as an angle "equivalent to the size of a euro coin on the Moon as seen from Earth." Space.com notes that the ESA launched a previous star-mapping mission in 1989; that satellite, Hipparcos, could measure the distances of bright stars within 3,250 light-years with a modest margin of error. Gaia will be able to measure up to 32,500 light-years away.