The Whirlpool Galaxy, also known as Messier 51a (M51a) or NGC 5194, is an interacting grand design spiral galaxy with a Sefert 2 active galactic nucleus. It lies in the constellation Canes Venatici and was the first galaxy to be classified as a spiral galaxy. It is 7.22 megaparsecs (23.5 million light-years) away and 23.58 kiloparsecs (76,900 light years) in diameter.