This one has been in the unprocessed back-catalogue for over 2 years. It was a bit tricky to process as the original subframes were made at two different sensor temperatures, so they needed separate preprocessing and later combination of calibrated frames. 

I've imaged it a few times but only processed the data once before -- in fact for this image I was simultaneously collecting data in a new "shed" observatory -- I haven't processed those yet.

I've always had a soft spot for this galaxy, ever since, as a teenager, I bought an educational pack, a so-called Jackdaw, called "The discovery of the galaxies". It was a great resource with reproductions of lots of contemporary material, including the original observation by William Parsons, the 3rd Earl of Rosse, with his 72" reflector, which showed the spiral nature for the first time (and one of his drawings featured on the cover). Apparently these Jackdaws still exist: see https://rosenclassroom.com/product/discovery-galaxies-0?isbn=9781566961868.

The galaxy, M51 or NGC 5194, is called the called the Whirlpool Galaxy for fairly obvious reasons. It's rather close, at 23 million light years, and has a smaller companion, NGC 5195 with which it is very obviously interacting.

It was first discoverd by Charles Messier on 13 Oct 1773 and was entered into his catalogue as M51. When Rosse discovered its spiral nature in 1845 it was still not evident that it was outside our galaxy -- indeed the concept of separated galaxies was unknown at the time. It became the first of a class of objects which were called "spiral nebulae". In my youth some older astronomy books still used that term and others referred to galaxies as "island universes".