The Dog Star
Why do some stars appear brighter than others? Broadly speaking the apparent brightness of a star comes down to two factors: luminosity and distance. The star Sirius is both intrinsically bright and quite close to us, making it the brightest star visible in the entire sky.
Stars go through a life cycle that causes changes in their surface brightness at different stages, so even bright Sirius won’t appear constant forever. Sirius is actually a star system comprised of two stars: the brighter is called Sirius A, and its much fainter companion Sirius B, though don’t expect to see it through backyard equipment.
The Sirius system is also relatively close to us, at just over 8 lightyears away the Sirius system is the 5th overall closest star to Earth.
On Winter nights it can be seen at the head of Canis Major, the Great Dog, loyally following Orion across the sky on his westward journey. The name Sirius comes from a Greek word meaning “scorching” and it certainly lives up to its name! Sirius is also commonly referred to as the Dog Star, because of its position at the head of Canis Major.
In fact, when the ancient Egyptians noticed Sirius rising just before dawn in mid-July it served as a convenient reminder that the Nile’s annual flooding would soon begin. You might have heard the term “dog days of summer” to refer to the late summer, the origins of this phrase referring to the general period when the Dog Star would become visible mid-July!
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Stay well, and clear skies!