I took this picture on 20th April 2015, and finally got around to processing it today, using my new favourite software PixInsight.

A good example of a spiral galaxy, M51 is 23 million light years from earth.  If you look carefully you can tell there is another smaller galaxy (NGC 5195) interacting with it at the top of one arm.

The Whirlpool galaxy has a diameter of around 75,000 light years, and so is about three quarters the size of our own galaxy the Milky Way.

 

M51 Whirlpool Galaxy