Who hasn’t heard of the Dog Star, Sirius? In February, it’s the brightest star in Earth’s night sky, parading overhead from nightfall until midnight. When viewing Sirius, we’re actually seeing the combined light of two stars. Learn how to find Sirius.
Sirius is the alpha dog of the Big Dog constellation (Canis Major) and the brightest star of February. This star was considered bad news in the Roman Empire, where they sometimes sacrificed dogs to protect their wheat crops from disease thought to be brought about by Sirius! Even Dante wrote of “the scourge of days cannicular.”
The Dog Star had better press in ancient Egypt, where they believed an alliance between the sun and that brightest star caused summer’s heat. Even today we still use the expression “Dog Days” to mean sultry weather. Read our article on the “Dog Days of Summer.”
How to Find Sirius
During February evenings, Sirius shines all night. Look towards the southern skies. It’s hard to miss.
If its great blue-white brilliance isn’t enough, you can identify Sirius thanks to Orion’s famous belt, which points downward diagonally at it.
Image: Sirius (bottom center) and Orion (upper right) shining above the forest in a winter sky. Orion’s belt points almost directly at Sirius. Credit: Erkki Makkonen.
When viewing Sirius, we’re actually seeing the combined light of two famous stars. Circling each other like slow dancers, the pair are wildly different in brightness, and during the next five years are most widely separated as they swing through their lopsided 50-year orbit.
- Sirius B is a tiny star only the size of Earth yet with a weight equal to our sun. This means it’s packed to an amazing density. A lollipop made of its material would outweigh a car.
- But it’s the main star, Sirius A, which is 10,000 times brighter than its companion, that makes Sirius such a lighthouse. As the nearest blue-hot sun to Earth, its beautiful diamond dazzle arrives after just an 8 ½ year journey through space.
The magnitude of Sirius is the brightest at -1.44 (remember: the smaller the number, the brighter the star). There are brighter stars than Sirius in the cosmos, but they are much farther away, so they appear dimmer from Earth.
Image: Sirius, the Winter Triangle, and Orion. Credit: Matsumoto.
Because Sirius as a two-dog star is so bright, it tends to twinkle and even change color as it shines through Earth’s atmosphere, flickering in a rainbow of colors.
Step out any time and check it out. You’ll be a happy puppy.