The Whirlpool Galaxy (M51)
The Whirlpool Galaxy was the first galaxy to be classified as a spiral galaxy. It is an interacting grand-design spiral galaxy with a Seyfert 2 active galactic nucleus, paired in the sky with its companion NGC 5195.
Briefing
The Whirlpool Galaxy—Messier 51a (M51a), also catalogued as NGC 5194—is a galaxy in the constellation Canes Venatici. It is described as an interacting grand-design spiral galaxy with a Seyfert 2 active galactic nucleus, about 31 million light-years (9.5 megaparsecs) away and about 23.58 kiloparsecs (76,900 light-years) in diameter.
How we know
The Whirlpool Galaxy entered astronomy’s working record as an object that could mislead comet hunters: Charles Messier discovered it on October 13, 1773, while searching for such confusions, and placed it in his catalogue as M51. Its significance as a spiral rests on classification—recognizing a galaxy’s structure by observing its form—and it has since been “extensively observed by professional astronomers,” specifically as a system interacting with its companion NGC 5195, which is studied to understand galaxy structure (especially structure associated with spiral arms) and galaxy interactions; the pair is also a favorite subject of galaxy interaction models.
- Field conditions
- Located in the constellation Canes Venatici. The Whirlpool Galaxy and its companion NGC 5195 are described as easily observed by amateur astronomers, and can be seen with binoculars.
