Ready for Hubble's largest ever photomosaic? Over the course of a decade, scientists compiled about 600 Hubble images of our nearest major galactic neighbor, the Andromeda Galaxy. This 2.5-billion-pixel image allows astronomers to study its individual stars, and uncover Andromeda's history of galactic collisions and mergers, all in meticulous detail. Andromeda's headed our way, too. In about 4.5 billion years, it'll merge with our home galaxy, the Milky Way. In the meantime, we can use Hubble's