Winter Triangle

January 03, 2020

Around 9pm, look low to the southeast to find the brightest star in the night sky. Bright white, twinkling Sirius. Above it, you’ll see that iconic winter constellation Orion the Hunter. The orange star at his shoulder is the red supergiant Betelgeuse. Draw a line between Sirius and Betelgeuse, then look to the left, or east to find Procyon (PRO-see-on), another bright white star, and there you have it. A large, nearly perfect equilateral triangle of bright evening stars.

Now Procyon is pretty close—just over 11 light years away. But Sirius is even closer at just 8.5 light years away. The fact that they’re so close helps to explain why they’re so bright. But by most estimates, Betelgeuse is over 500 light years away. And its orange color indicates that it’s much cooler than the other two stars. So why is it so bright?

There are a lot of reasons, but one is that it’s ENORMOUS. If you were to put Betelgeuse where the sun is, it would engulf the orbits of all four inner planets, the asteroid belt, and by some estimates, even Jupiter.

And Betelgeuse has been getting a lot of attention lately not because of how bright it is, but how dim it’s getting. This has some astronomers speculating whether the star is collapsing, which could result in its ultimate demise… a supernova which would be as bright as the full moon and visible in the daytime for months. But not so fast… Betelgeuse has been known for centuries to vary in brightness for a number of reasons. This is just one unlikely explanation among many others… but it is probably the most fun.