 Welcome to our segment on Interacting Galaxies. Here's our old friend Andromeda. As we noted in earlier segments, Andromeda is heading towards the Milky Way. Andromeda will collide with the Milky Way and start a one billion year long collision process. But if you recall from our discussion about how far away stars are in a galaxy, for example, our nearest star, Proxima Centauri, is four light years away. Those large distances between stars means that it's a million to one shot that any star will actually collide when the galaxies pass through each other. But the form, the shape, will change dramatically and change forever for the interacting galaxies themselves. The key factors are the shapes and relative masses of the colliding galaxies, the colliding velocity, and the angle of the collision, a glancing blow versus a head on collision. They'll have different outcomes. I'd like to show you a few of the over 100 interacting galaxies photographed by the Hubble Space Telescope.