Gaia satellite to map Milky Way launched into space
19 December 2013 Last updated at 10:03 GMT
Europe has launched the Gaia satellite - one of the most ambitious space missions in history.
The 740m-euro (£620m) observatory is going to map the precise positions and distances to more than a billion stars.
This should give us the first realistic picture of how our Milky Way galaxy is constructed.
Gaia's remarkable sensitivity is also expected to lead to the detection of many thousands of previously unseen objects, including new planets and asteroids.