By comparing scans of the sky taken six months apart, researchers are able to triangulate and measure stars' distances using the parallax effect, a technique that dates back to ancient Greece.


In the first release of Gaia's catalogue, more than two million stars have been labeled both with measurements of their distances from the Sun and their motion, obtained by comparing Gaia data with those from Hipparcos.


In future releases, the catalogue will grow to include the distances and velocities of more than one billion stars.


With more years of observation, Gaia's measurements will become so accurate that the distances of many of the Galaxy's stars will be pinpointed to within 1%.

"What Gaia is going to do is going to be phenomenal," says Wendy Freedman, an astronomer at the University of Chicago in Illinois. "It will be the fundamental go-to place for astronomers for decades to come."