Whirlpool Galaxy, M51a
The Whirlpool Galaxy, M51a and companion M51b
(credit NASA, ESA, S. Beckwith (STSci), and the Hubble Heritage Team(STSci/AURA),The Hubble Space Telescope ACS.)
The Whirlpool Galaxy is one of the most famous galaxies in the sky, having been discovered by Charles Messier in 1774 and designated in the Messier catalog as M51. In 1781 the companion galaxy, NGC 5195, was discovered by Pierre Mechain. The Whirlpool Galaxy and its companion are often designated M51a and M51b. The distance to the galaxy is about 23 million light-years.