Whirlpool Galaxy

The Whirlpool Galaxy, also known as Messier 51a (M51a) or NGC 5194, is an interactinggrand-designspiral galaxy with a Seyfert 2active galactic nucleus. It lies in the constellationCanes Venatici, and was the first galaxy to be classified as a spiral galaxy. It is 31 million light-years (9.5 megaparsecs/Mpc) away and 23.58 kiloparsecs (76,900 ly) in diameter.

The galaxy and its interaction companion, NGC 5195, are easily observed by amateur astronomers; the two galaxies may be seen with binoculars. The Whirlpool Galaxy and NGC 5195 have been extensively observed by professional astronomers, who study the pair to understand galaxy structure (particularly structure associated with the spiral arms) and galaxy interactions. This pair is among the most famous and relatively close interacting systems, and thus is a favorite subject of galaxy interaction models.