This week, in the hour just before dawn, Sirius shines high in the southern sky, just southeast of the Orion constellation. The brightest star in the night sky, Sirius is "only" 8.6 light years from Earth; if it exploded 8 years ago, we won't know until next May.
Actually, Sirius is a binary star system, composed of a large, bright Sirius A star, twice the mass of our sun, and a small, faint Sirius B, only the size of Earth but possessing the mass of our sun. Astronomers believe that the duo formed about 250 million years ago (very recent in the history of the Universe) and that Sirius B, originally a red giant (five times the size of our sun), collapsed into a dense, white dwarf about 120 MYA. The two stars orbit each other every 50 years and are separated by a distance equal to the radius of Uranus' orbit around the sun; of course, from our vantage point, they appear close together.
Also known as the Dog Star, Sirius represented Orion's hunting companion to early human civilizations. Though we now understand its identity and location with more scientific accuracy, it is no less brilliant and no less inspiring.
