Credit: NASA/JPL-Caltech/R. Kennicutt (Univ. of Arizona)

This visible light view of the spiral galaxy M51 comes from the Kitt Peak National Observatory 2.1m telescope, and measures 9.9 by 13.7 arcminutes (north up). A four-color composite, the visible light image shows emissions from 0.4 to 0.7 microns, including the H-alpha nebular feature (red in the image).

The targeted galaxy is known by various names: M51 from its Messier catalog designation, and also as NGC 5194. M51 was one of the original discoveries of Charles Messier, found in October 1773 while he was observing a faint comet. The Messier catalogue of galaxies is named after him. Colloquially, M51 is also known as the "Whirlpool Galaxy", or "Rosse's Galaxy," after Lord Rosse, who first detected galaxy spiral structure in his observations of M51. The companion, NGC 5195, was discovered in 1781 by Pierre Mechain.

The Whirlpool galaxy is a favorite target for amateur and professional astronomers, alike, and was the first light target for the Infrared Space Observatory. Found in the constellation Canes Venatici, M51 is 37 million light-years away..