Sirius is one of the brightest stars in the night sky and is part of the constellation Canis Major. It is also known as the Dog STAR and is the brightest STAR in the night sky, outshining even the planet Venus. Sirius is a binary STAR system, consisting of two stars orbiting each other, with the brighter STAR being Sirius A and the dimmer STAR being Sirius B. The term 'Sirius is one' refers to the fact that Sirius A is the only STAR visible to the naked eye.