About the Object:

The Whirlpool Galaxy has an interesting history in terms of its discovery, classification, and its contributions to our knowledge of galaxies in general. The galaxy was first cataloged by Charles Messier in 1773 and its companion, NGC 5195, was discovered a few years later by Pierre Méchain in 1781. At the time, it was not known that the two "nebulae" were interacting. Nobody knew whether their close position in the sky was coincidence, with one a distant background object and one foreground, or whether they were actually close together.

Then, in 1845, using the 72 inch "Leviathan of Parsontown", William Parsons became the first person ever to observe the spiral structure of a galaxy--it was M51, the Whirlpool. This was the first step in determining that so-called "spiral nebulae" are, in fact, separate island universes not just diffuse nebulae within our own Milky Way. With the advent of radio astronomy, the interactions between the two galaxies were first discovered leading to a long history of this Arp interacting pair of galaxies providing information on how galaxy interactions affect structure and evolution.