The above image of the Whirlpool Galaxy is a collaborative project between my friend Preston Starr of Keller, Texas and myself. Preston captured the image from his observatory west of Ft. Worth, Texas using his new AT 12-inch Richey Cretien OTA. I performed the post image processing using CCDStack and Photoshop CS2.
M51 is actually two galaxies. The larger galaxy (M51A) is designated NGC 5194 and the smaller galaxy (M51B) is designated NGC 5195. M51 is located near the end star (Alkaid) in the Big Dipper's handle at an estimated distance of 31 million light years.
M51A and M51B have interacted gravitationally and this interaction has distorted the structure of the larger galaxy. From our point of view M51B, the smaller galaxy, is actually behind M51A and is receding from the larger galaxy. Some astronomers believe the smaller galaxy has been captured by and is now in an elongated orbit around the larger M51A. Computer simulations of the interaction of these two galaxies support this conclusion.