Of all the fixed stars in the night sky, Sirius is by far the brightest – almost twice as bright as its nearest rival, the star Canopus, which lies too far south to be viewed from most of the Northern Hemisphere. Only the Sun, Moon and the planets Venus, Jupiter and, at times, Mars, appear brighter. Sirius, with its flashing brilliance, is a striking feature of the northern winter sky and has understandably drawn the attention of observers of the night sky for thousands of years.

Sirius has many names. Astronomers recognize over fifty designations for the star, but the most commonly used is Alpha Canis Majoris, the brightest star in the constellation Canis Major. This is Latin for the 'Great Dog', which has led to its popular nickname the ‘Dog Star’. Over the centuries many beliefs have come to be associated with Sirius. Some of these beliefs still echo in such phrases as ‘the dog days of summer’, which the ancient Romans understood well. Other old beliefs long ago fell from public consciousness — only to be revived and to grow into modern popular and scientific controversies. Although these beliefs may seem quite recent, many have their origins in the ancient lore surrounding Sirius; humans seem naturally drawn to its brilliance, and a surprising number of modern cults have nucleated around beliefs in which Sirius plays a prominent role.