Getting Sirius: The Low-Down on the “Dog Star”

A spectacular sight in the cold dark sky of a northern winter, blue-white Sirius shines as the brightest star save for the Sun. Its name comes from the ancient Greek seirios, “scorcher”. As the most prominent in Canis Major (the Big Dog), Sirius is often called the “Dog Star”.

The Basics

• Twice the mass and 25 times more luminous than the Sun, Sirius is a modest star as stars go. It’s not as intrinsically bright as monster stars like Rigel and Deneb. It simply appears bright because it’s the 5th closest star to Earth, only 8.6 light-years away.

• In the 19th century, the German astronomer Bessel determined there was an unseen companion orbiting Sirius. Telescope maker Alvin Clark first spotted the dim companion in 1862. It’s now called Sirius B; the bright star we see is called Sirius A.

• Through a small telescope, you can see Sirius in the daytime. With clear dry skies, you may even spot it without a telescope if you know exactly where to look.

A Deeper Look

• Early in the 20th century, astronomers determined Sirius B was as massive as the Sun, but had a radius roughly the same as Earth. It was therefore extremely dense, about 125 tonnes per cubic centimeter! And it was faint… 400 times less luminous than the Sun. As it turns out, Sirius B is a white dwarf, a dense burned-out husk of star that’s collapsed onto itself.

• Until 120 million years ago when it faded from view, the dim Sirius B outshone Sirius A… what a sight they must have been together!

• Sirius A will itself become a red giant then a white dwarf in a billion years or so.

A Bit of History

• Although many think of Sirius as a winter star, the ancient Romans and Greeks associated Sirius with the heat of summer because it rises just before dawn near the summer solstice. According to Virgil, its influence was considered unfortunate, bringing “drought and diseases on sickly mortals”

• Many ancients including Homer described Sirius as reddish, likely a result of its dramatic twinkling as it rises. But of course, Homer also saw “wine-dark seas” around Greece, a result of either poetic license… or poor eyesight!

Personal View

After 35 years looking at the stars and seeing all many of fantastic things through a telescope, the beauty of Sirius twinkling in the south-east on a dark, frosty winter night still stops me in my tracks and fills me with the same wonder I felt when I was nine years old. Learn the stars and they will be your friends for your entire life.