From HubbleCast. Scientists have been using Hubble observations to predict the future of the Andromeda Galaxy and the Milky Way, and how the collision will look from Earth. Projecting the motion of Andromeda's stars over the next 8 billion years, the astronomers now know the path that galaxy is taking through space. And it's heading straight for us! Computer simulations based on Hubble observations show how the two galaxies will crash together in around 4 billion years' time.The Andromeda Galaxy, some 2.2 million light-years away, is the closest spiral galaxy to our home, the Milky Way. For around a century, astronomers have known it is moving towards us, but whether or not the two galaxies would actually collide, or simply fly past each other, remained unclear. Now, a team of astronomers has used the Hubble Space Telescope to shed light on this question, by looking at the motion stars in the Andromeda Galaxy.We wanted to figure out how Andromeda was moving through space. So in order to do that we measured the location of the Andromeda stars relative to the background galaxies. In 2002 they were in one place, and in 2010 they were in a slightly different place. And that allowed us to measure the motion over a period of eight years.The motion is actually incredibly subtle, and not obvious to the human eye, even when looking at Hubble's sharp images. However...