Here's another attempt at Messier 51, the Whirlpool Galaxy. I wasn't happy with my effort in April so I tried again last Sunday night, when we had about 4 hours of clear skies but under a bright three-quarter moon. This is the result of 106 minutes of exposure time, plus another 90 minutes of correction exposures (darks and flats). Though it's a relatively short session there is plenty of structural detail in the image, especially in showing the huge size of the halo surrounding the galactic core.

I'm plagiarizing Wikipedia here:

The Whirlpool Galaxy, also known as Messier 51 or NGC 5194, is an interacting grand-design spiral galaxy with a Seyfert 2 active galactic nucleus. It lies in the constellation Canes Venatici, and was the first galaxy to be classified as a spiral galaxy. It is 7.22 megaparsecs (23.5 million light-years) away and 23.58 kiloparsecs (76,900 light years) in diameter.