Representing the ancient Greek hero of the same name, this is a large constellation of the Northern hemisphere. It contains the famous variable star Algol (Beta Persei, in the center of its "body"). This star varies between magnitude 2.1 and 3.4 with a cycle of just over two days. This is because it is an eclipsing binary, a system of two stars in a mutual orbit which eclipse each other as seen from Earth, blocking the eclipsed star's light for a short time. The Milky Way passes through Perseus, so it contains nebulae (red) and star clusters.