Use the Big Dipper to Identify Two Bright Evening Stars

May 24, 2019

And now for two bright stars... and how to find them. I'm Matt Pelsor, and this is your Weekend Sky Report. Arcturus and Spica are two of the brightest stars in the northern hemisphere, so they're not hard to see... but if you're new to Astronomy, you can use this mnemonic device to find them: Arc to Arcturus, and Spike to Spica. Here's what I mean... First, find the Big Dipper, then follow the curve of the handle, or arc that it makes to bright orange-white Arcturus. From there, continue that same direction, but with a more laser-straight line to bluish white Spica. Arc to Arcturus, then spike to Spica. Arcturus is just slightly more massive than our sun, but it's more than 25 times larger, and more than 150 times brighter. This is because it has entered the next stage of its life... all of its core hydrogen has been used up and it's puffed up to many times its original size. The same thing will happen to our sun in a few billion years. Spica makes up the right hand of the constellation Virgo. In some interpretations, it represents an ear of wheat in Virgo's right hand. It's easily the brightest star in the constellation... and actually, it's two stars. Spica is a spectroscopic binary... meaning it's two stars that are so close together, you can't split them with a telescope. Because they're so close, they orbit each other very quickly. Each orbit takes only 4 days. What's more, the gravitational forces each star has on the other makes them more egg-shaped than spherical. But again, you won't be able to tell that from looking at it through a telescope. When you find Spica, you'll be looking at a star almost 2000 times brighter than our sun. I'm Matt Pelsor... happy skywatching.