For the first time, astronomers have a reliable map of the heavens

Our galaxy, far far away FOR something so enormous, astronomers know remarkably little about the Milky Way, Earth's home galaxy. They know its rough dimensions--somewhere between 100,000 and 180,000 light-years across. And they know that it contains 100bn stars--or perhaps 200bn, or maybe even twice that again. For part of the galaxy, though, things are about to become much clearer. On April 25th the European Space Agency's Gaia satellite released one of the biggest chunks of data in the history...