When: Summer 2012 from Kourou, French Guiana
Who: ESA
What: One giant spacecraft
Where: Orbiting at L2, or 1.5 million kilometres from Earth
Why: To make a 3-D map of our Galaxy
How: astrometry, photometry and spectrometry

Although we live here, we still don't know the history of our Galaxy. Over a hundred billion stars call the Milky Way home, including our star, the Sun. Each of those stars has a story to tell us about the Galaxy we live in. (For more about galaxies, please read our Galaxies and the Universe tutorial.)

Astronomers have watched thousands of the stars near to the Sun and have learned much about how stars are made, shine and are destroyed.  A new space mission called Gaia offers the chance to look at a billion more stars all the way to the centre of the Galaxy. The picture it will paint will fill a lot of the gaps in our knowledge about the Milky Way.

Updating an Old-fashioned Galaxy Recipe
For example, we really do not know how galaxies like our own are formed. Instead space scientists have been using a dog-eared recipe that not everyone enjoys anymore.

The recipe they've been using goes something like this: Take a hefty amount of dark matter. Let it draw in gas particles from the universe. Stir briskly. Leave it to clump and make little stars all over the place. Collapse the core until it forms supergiant stars that blow away gas from the centre. Whip that gas out into the clumpy arms where it shocks them into making bigger stars. Tah-dah! A spiral galaxy. Serves 100 trillion.

This recipe has lost its popularity as telescopes have shown us younger and older galaxies. Like seeing the steps of someone else's dinner prep, these galaxies look a lot different than our recipe would predict.

For example, astronomers have seen a fairly standard looking galaxy that in different light is clearly the result of a sandwich of two or more galaxies. Also, some young, small galaxies have never been stirred. Humph.

Charting of Stars
The Gaia mission will aim every kind of instrument at every star it can see clearly and relay those data back to Earth. Gaia's eyes will see the star's position, chemical makeup, brightness and colour. Astronomers can use all of this in various combinations to determine each star's age, temperature, distance, and movement.

With a billion pieces of this three-dimensional puzzle, astronomers will be able to trace back the events that made our Galaxy the size, shape and makeup that we see today.

Careers
If you are interested in the career and/or educational opportunities arising from the Gaia mission, here is a list of UK participants: University of Cambridge, University of Leicester, University of Edinburgh and University of Brunel, Rutherford Appleton Laboratory and University College London's Mullard Space Science Laboratory (MSSL).