The Whirlpool Galaxy is a spectacular sight, residing in the constellation of Ursa Major, over 35 million ly from us. At first sight, it appears to be two galaxies joined together, but the galaxy to the left is in fact NGC 5195 and is in the background compared with M51. NGC 5195 is partly hidden from us by dust clouds in M51, and is receding from us following a collision with M51, hundreds of millions of years ago. As a result of this collision, MGC 5195 was severely deformed, and the shape of M51 was changed as the spiral arms opened out. M51 is similar in size to our own galaxy, being around 100,000 ly across.