What we call M51, aka the Whirlpool Galaxy, is actually an image of 2 potentially interacting galaxies, NGC5194 and NGC 5195. It is likely that the smaller member, 5195, is further away, since the dust lanes from the Whirlpool seem to cross in front of it. Also note several tiny backround galaxies in this image. Tucked within the handle of the Big Dipper, but actually a denizen of Canes Venatici, not Ursa Major, M51 is one of the most photographed deep sky objects, and my personal favorite since childhood…who can call himself “astrophotographer” without having conquered the Whirlpool!
Technical details are as follows:
Imaged with a 16″ RCOS @ f/9, SBIG STL11K, and Paramount ME by SSRO at New Mexico Skies in the spring of 2008. Assembled as an (HaL)(R+Ha)GB with 15 hrs Lum, 3 hrs/channel RGB, and 7.5 hrs Ha. Calibration in Maxim, alignment in Registar, and integration with Sigma Combine. Everything else in Photoshop.