M31

From Slackerpedia Galactica

M31 is a freaking huge and nearby galaxy also known as the Andromeda Galaxy. It was originally called the Andromdea Nebula before it was understood that there was even such things as galaxies. Edwin Hubble originally proved that it was much further away than would be possible if it was in the Milky Way. It is now known to be about 2.5 million light years away and on a collision course with you.