If you’ve ever spotted a really bright star low in the southern sky during winter (in the northern hemisphere), there’s a good chance you were looking at Sirius. It’s the brightest star in Earth’s entire night sky - about twice as bright as any other.
There are two reasons Sirius shines so brilliantly. One: it’s intrinsically a bright star, about 25 times more luminous than our Sun. Two: it’s incredibly close - only 8.6 light-years away. Most “bright” stars in our sky are bright because they’re huge and far away, like Betelgeuse. Sirius is the rare combination of “fairly big” and “really close.”
Sirius isn’t alone. Through a powerful telescope, you can see it has a tiny companion called Sirius B - a white dwarf, the dense burnt-out core of a star that died long ago. The two stars orbit each other every 50 years. The ancient Egyptians paid special attention to Sirius; its first appearance just before sunrise each summer marked the coming flood of the Nile, the beginning of their year.
