Astronomers are about to unfold a new map of cosmic reality. The Gaia spacecraft, launched in late 2013 by the European Space Agency, is on a five-year mission to chart the heavens in unprecedented detail—and the first set of coordinates has been released. By the end of Gaia's run, it will have pinpointed the positions of approximately one billion stars in the Milky Way and nearby galaxies with a resolution so high it can spot objects as small as five microarcseconds—roughly half the size of a dime sitting on the moon as seen from Earth.
