Who hasn鈥檛 heard of the Dog Star, Sirius? In February, it鈥檚 the brightest star in Earth鈥檚 night sky, parading overhead from nightfall until midnight. When viewing Sirius, we鈥檙e 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 鈥渢he scourge of days cannicular.鈥
The Dog Star had better press in ancient Egypt, where they believed an alliance between the sun and that brightest star caused summer鈥檚 heat. Even today we still use the expression 鈥淒og Days鈥 to mean sultry weather. Read our article on the 鈥淒og Days of Summer.鈥
How to Find Sirius
During February evenings, Sirius shines all night. Look towards the southern skies. It鈥檚 hard to miss.
If its great blue-white brilliance isn鈥檛 enough, you can identify Sirius thanks to Orion鈥檚 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鈥檚 belt points almost directly at Sirius. Credit: Erkki Makkonen.
When viewing Sirius, we鈥檙e 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鈥檚 packed to an amazing density. A lollipop made of its material would outweigh a car.
- But it鈥檚 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 1/2 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鈥檚 atmosphere, flickering in a rainbow of colors.
Step out any time and check it out. You鈥檒l be a happy puppy.
Spot more of February鈥檚 stars! See our February Sky Map.