How bright is a star?
Go outside and look at the stars and notice – how bright is a star?
If you stargaze for long enough, you will notice that some stars are bright and some stars are dim. Some even have different colors ranging from bluish white to red.
The brightest star in the northern sky is called Sirius
Sirius in the constellation of Canis Major (the Big Dog). It's a bright white star marking the dog's collar. In the constellation of Orion, there is an orange star marking the hunter's left shoulder called Betelgeuse. If you look at the picture, you can see that Sirius looks brighter than Betelgeuse. BUT … Betelgeuse is actually 26,000 times brighter than Sirius! How is it possible?
How could Sirius look brighter if it's actually way dimmer? It's because of distance. Sirius is about 8 light years away (that's 48 trillion miles), while Betelgeuse is about 700 light years away (4.2 quadrillion miles). Because Betelgeuse is so much further away, it looks dimmer than Sirius.
This is what astronomers have to think about when they look at objects in space
They have to figure out if it's really bright or if it's just close to us. Is that star really dim or is it just really far away? One of the largest and brightest stars in our galaxy is also in Canis Major, but you can't see it with your eyes. It's called VY Canis Majoris. This star is SO big that if you put it in the solar system instead of the Sun, VY Canis Majoris would swallow up every planet from Mercury through Saturn! So why can't we see it? It's 3,900 light years away (more than five times further than Betelgeuse).
Now the next time you're looking at the stars, think about how bright they might really be!
Dr. Teri Gee is the Manager of the Barlow Planetarium in Menasha, Wisconsin. The Barlow Planetarium offers weekly public Star Shows and Laser Shows, along with family events, educational programming, and field trip experiences that inspire a love of science and the night sky. Learn more about Barlow Planetarium at barlowplanetarium.org.
