Perseus, in astronomy, northern constellation lying E of Cassiopeia and N of Taurus. It contains the bright star Mirfak (Alpha Persei) and Algol (Beta Persei), a visible variable star of the type known as an eclipsing variable. Perseus contains two star clusters (NGC 869 and NGC 884) that are visible to the naked eye, as well as an open cluster (M34) that is barely visible. A meteor shower known as the Perseids appears to radiate from a star in Perseus; this shower can be seen every year for several nights beginning Aug. 10, after midnight. In 1901 a brilliant nova was observed in the constellation. Perseus reaches its highest point in the evening sky in late December.