Sirius, the leading light of Canis Major, the big dog, scoots low across the south on winter nights. It’s also the brightest star in the entire night sky, in large part because it’s a close neighbor — less than nine light-years away. Several of the other stars that outline the dog are far more impressive. In fact, a star that’s close to the right of Sirius is probably more than a thousand times brighter. But its light is dimmed by its distance — about 500 light-years. Mirzam shines so brightly because it’s much bigger and hotter than the Sun. The greater size means there’s a lot more surface to radiate energy into space. And the hotter temperature means that a given surface area on the star radiates more energy than the same size patch on the Sun. The star is also much heavier than the Sun — perhaps 15 times the Sun’s mass — so it “burns” through the nuclear fuel in its core in a hurry. So even though Mirzam is less than one percent of the age of the Sun, it’s already nearing the end o
