Whirlpool galaxy
37 Million light years away
"the spiral structure is a result of M51's current encounter with its neighbor, NGC 5195.
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. Halton Arp has included M51 as No. 85 in his Catalogue of Peculiar Galaxies as "Spiral with Large High-Surface-Brightness Companion". -SEDS.ORG

Image taken with ST2000XM with Astrodon LRGB i-series filters
William Optics FLT110 f/ 7 on a Losmandy G11 with Gemini
Luminance: 2 mins x 15, Red, Green and Blue channel: 2 mins x 8
Images aligned, dark frame and flat field processed with AIP4WIN
Final Image processing with PS CS2
Taken on April 21, 2007 in Jackson, Ohio