June 21, 2012
Ah, autumn. There’s a nip in the air, and practically every local radio and television station, newspaper, and coworker hanging out at the water cooler is talking about the plight of OSU football. As I think of the upcoming game with that “team up north” (and I try not to think about it much, truth be told), my mind turns to thoughts of … binary stars. So I’m an astro-nerd. Sue me.
Still, you’ll find a connection between the giant hydrogen bombs called stars and large young men running around after an inflated pigskin, but it’s not one designed to increase the popularity of astronomy among the gridiron-obsessed in Central Ohio.
Even a small department-store telescope will show you what I mean. The star Almach is relatively easy to find because it is visible to the unaided eye. Around 7:15 PM, look high in the southeast for the large assembly of four stars in a rough square called the Great Square of Pegasus. Find the leftmost star in the Great Square and look left for the star Almach. (A star map will help you here – or a trip to Perkins Observatory, hint, hint.)
You’ve found Almach, or Gamma Andromedae, not just a star but also a star system 200 light years distant from planet Earth. (One light year is about 6 trillion miles. You multiply it out. I have to watch the game). At that distance, it is one of the closer stars to us.
Your small telescope will reveal that Almach is not one star but two, i.e., a binary star. Such “doubles,” as they are sometimes called, are locked in a gravitational embrace. The dimmer, smaller star is forever fated to orbit the other.
Star B, the dimmer one, is about 60 billion miles from the brighter Star A. That’s about 600 times farther than our Earth is from the sun. The result is that B takes at least a few thousand years to complete one circuit around A. If you want to know the vastness of the universe, consider that the tiny gap you see between the two stars represents billions of miles.
As it turns out, Almach is not merely a double but a quadruple star system. In 1842 astronomer Otto Struve discovered that Star B is itself a close double star. Orbiting B at an average of 3 billion miles is Star C, invisible to all but the largest of amateur telescopes. That’s relatively close — about the same distance as the planet Neptune is from the sun. As a result, C takes only a few hundred years to complete one orbit around B.
If that distance sounds unusually close, consider that Star B has another companion that’s even closer. Star D is only a million miles from B, about one hundredth the distance of Earth to the sun. D zips around B in less than three days, practically skimming the surface of B. You won’t see D in any telescope. We only know about it because of the slight wobble it produces in the movement of B around A.
Almach may seem like a strange bird, but it isn’t. In fact, most stars you see in the nighttime sky are at least double and many are multiple systems. Our sun is the odd star out, a so-called “bachelor” star, as it wanders alone and forlorn in the universe.
So what’s the connection with football? On one level, the stars orbit each other, wheels within wheels, like some complex chalkboard design for the strangest football play ever designed.
However, that’s not what I mean. The B star in the main pair is a brilliant blue. Star A, the brighter one, glows yellow. One might even call its color maize. Yes, OSU fans, there they are. The University of Michigan school colors for all the cursed world to see, with nary a scarlet and gray pair to illuminate the dismal, dark skies of autumn.
Tom Burns is director of Ohio Wesleyan University’s Perkins Observatory in Delaware. He can be reached at firstname.lastname@example.org.