This galaxy is a very popular target for astro imagers.

The famous Whirlpool galaxy M51 was one of Charles Messier's original discoveries: He discovered it on October 13, 1773, when observing a comet, and described it as a "very faint nebula, without stars" which is difficult to see. Its companion, NGC 5195, was discovered in 1781 by his friend, Pierre Méchain, so that it is mentioned in Messier's 1784 catalog: `It is double, each has a bright center, which are separated 4'35".

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 spring 1845 by Lord Rosse, who made a very careful and acurate painting. Therefore, M51 is sometimes referenced as Rosse's Galaxy or Lord Rosse's "Question Mark" - he is cited with this name (see, e.g., NED).

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.

Date: May 2009
Location: St. Augustine, Florida
Optics: Ritchey-Chretien 10" f/7.35
Mount: AP 1200 GTO on Portable Pier
Camera: SBIG STl-6303E
Guiding: Astrodon OAG with Starlight Lodestar camera
Exposure: LRGB: Luminance: 6x15 minutes; RGB: 4x15 Minutes each unbinned.