This is “Looking UP! in southern Colorado,” from the Colorado Springs Astronomical Society. I’m Hal Bidlack, and there are lots of reasons to look up!
It’s Fall, the leaves are blowing in the wind, and Halloween is just around the corner. Seems like a great time to talk about the demon star! The star Algol lies in the constellation Perseus. And Algol is recorded as the winking eye of the severed head of the Gorgon Medusa.
You recall from Greek mythology Medusa was a creature with snakes for hair, whose stare could turn living creatures into stone. Our hero Perseus, after successfully sneaking in and cutting off her head, used Medusa’s deadly stare to turn Cetus the sea monster into stone. Now, Medusa is up in the northern sky, winking to observers on earth every couple of days. So what’s going on up there?
Happily, now we know. Lying at a distance of approximately 93 ly from Earth, Algol is not a single star, but rather is a set of three stars, Algol A, B, and C. Algol C orbits the other two once every two years or so, and doesn’t contribute to the varying light output. But Algol A and B have a very important relationship - they are what we call an eclipsing binary star system.
That means the two stars are rotating around a common center of mass and they are lined up in such a way that from Earth, they appear to pass one in front of the other regularly. Algol A is a bluish star about 90 times brighter than our sun, while Algol B is the “eclipser.” It’s a yellow star that is relatively dim, at only three times brighter than our sun, then Algol A. So when Algol B swings around in front of Algol A, it blocks much of the light, and from Earth, Algol appears to dim significantly. The eclipse takes just under 10 hours, and then Algol brightens up to its regular brightness. Pretty interesting behavior for a demon.
If you’d like to take a closer look at Algol or any of the other wonderful and amazing things in the sky, please visit KRCC.org or CSASTRO.org for a link to information on our monthly meetings and our free public star parties!
This is Hal Bidlack for the Colorado Springs Astronomical Society, telling you to keep looking up, Southern Colorado!
