A fixed star, in Medusa's head, in the constellation Perseus, remarkable for its periodic variation in brightness.
second brightest star in Perseus; first known eclipsing binary
Best known variable star, varying in brightness from about 2.2 to 3.5 magnitudes over a period of approximately 69 hours. It is in fact a binary system in which the two stars regularly cross in front of each other as viewed from Earth. Also known as the Demon Star.