Launch of Gaia, the 'billion star surveyor'
19 December 2013 Last updated at 09:00 GMT
Europe sends its Gaia mission into orbit to map the precise positions and distances to more than a billion stars.
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 will lead also to the detection of many thousands of previously unseen objects, including new planets and asteroids.
The European Space Agency (Esa) satellite is being sent up on a Soyuz rocket.