The Whirlpool Galaxy, also known as Messier 51 and NGC 5194, is an interacting grand-design spiral galaxy with an active galactic nucleus. It lies in the constellation Canes Venatici, and was the first galaxy to be classified as a spiral galaxy. Its distance is estimated to be 23 million light-years away from Earth. Some astronomers think that the Whirlpool’s arms are particularly prominent because of the effects of a close encounter with NGC 5195, the small, yellowish galaxy at the outermost tip of one of the arms. The compact galaxy appears to be tugging on the arm, the tidal forces from which trigger new star formation.