Right Ascension	13 : 29.9 (h:m)
Declination	+47 : 12 (deg:m)
Distance	37000 (kly)
Visual Brightness	8.4 (mag)
Apparent Dimension	11x7 (arc min)
Discovered by	Charles Messier Oct 13th, 1773

The famous Whirlpool galaxy M51 was one of Messier's original discoveries: He discovered it on October 13, 1773, when observing a comet. Its companion, NGC 5195, was discovered in 1781 by his friend, Pierre Mechain, so that it is mentioned in his 1784 catalog: `It is double, each has a bright center, which are separated 4'35". The two "atmospheres" touch each other, the one is even fainter than the other.' NGC 5195 was assigned an own number by William Herschel: H I.186.

M51 is the dominating member of a small group of galaxies. As it is about 37 million light years distant and so conspicuous, it is actually a big and luminous galaxy.

This galaxy was the first one where the spiral structure was discovered, in 1845 by Lord Rosse, who made a very careful and accurate painting. Therefore, M51 is sometimes referenced as Rosse's Galaxy or Lord Rosse's Question Mark. According to our present understanding, the pronounced spiral structure is a result of M51's current encounter with its neighbor, NGC 5195 (the fainter one in Messier's description). Due to this interaction, the gas in the galaxy was disturbed and compressed in some regions, resulting in the formation of new young stars. As is common in galactic encounters, spiral structure is preferably induced in the more massive galaxy.

For the amateur, M51 is easy and a showpiece if the sky is dark, but is quite sensitive for light pollution which easily makes it fade in the background. Under very good conditions, even suggestions of its spiral arms can be glanced with telescopes starting from 4-inch. Low magnification is best for viewing this pair.