One of the most familiar constellations of the northern sky and the third largest in area. It contains nineteen stars brighter than fourth magnitude. The seven main stars of the constellation form an asterism known variously as the Plough, the Big Dipper and Charles's Wain. The two stars Merak and Dubhe in the Plough are known as the Pointers since the line between them is effectively an arrow to Polaris, the Pole Star. Ursa Major is one of the ancient constellations listed by Ptolemy (c. AD 140). It contains a group of galaxies belonging to the Local Supercluster, including the relatively bright spiral galaxy, M81.
