Mirzam (Beta Canis Majoris) is the fourth brightest star in the constellation Canis Major. Its Arabic name (also spelled 'Murzim') suggests that it is an 'announcer' of Sirius, as Mirzam rises first, but the exact meaning is unclear. Mirzam is a hot giant B star, coming to the end of its core hydrogen fusion, and is one of the brightest of the variables known as Beta Cephei stars or, sometimes, after itself, as Beta Canis Majoris stars. It is also one of the local stars whose light is used as a background to study the interstellar medium, and lies along a sort of tunnel in which the gas is especially hot and thin.