M51 Widefield

The Whirlpool Galaxy (also known as Messier (opens in a new tab) 51a, M51a, or NGC 5194) is an interacting (opens in a new tab) grand-design (opens in a new tab) spiral galaxy (opens in a new tab) that is estimated to be 23 ± 4 million light-years (opens in a new tab) from the Milky Way Galaxy (opens in a new tab) in the constellation (opens in a new tab) Canes Venatici (opens in a new tab). It is one of the most famous galaxies in the sky. The galaxy and its companion (NGC 5195 (opens in a new tab)) are easily observed by amateur astronomers (opens in a new tab), and the two galaxies may even be seen with binoculars (opens in a new tab). The Whirlpool Galaxy is also a popular target for professional astronomers, who study it to further understand galaxy structure (particularly structure associated with the spiral arms (opens in a new tab)) and galaxy interactions.

What was later known as the Whirlpool Galaxy was discoveredon October 13, 1773 by Charles Messier (opens in a new tab), and is designated as M51 (opens in a new tab). Its companion galaxy, NGC 5195 (opens in a new tab), was discovered in 1781 by Pierre Méchain (opens in a new tab). It was however not until 1845 that the Whirlpool became the first to be recognized as a spiral. This was achieved by Lord Rosse (opens in a new tab) employing a 72-inch (~1.83 m) reflecting telescope (opens in a new tab) which he constructed at Birr Castle (opens in a new tab), Ireland. Sometimes M51 is used to refer to the pair of galaxies, in which case the individual galaxies may be referred to as M51A (NGC 5194) and M51B (NGC 5195).