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Ophiuchus, the serpent bearer, must be a bit dizzy. His “head” — the star Rasalhague — spins at more than a half million miles per hour. That’s almost fast enough to tear the star apart.
Rasalhague is actually a binary system — two stars locked in a mutual orbit. They’re so close together, though, that astronomers couldn’t get a good reading on the individual stars until a few years ago.
The smaller star is a little less massive than the Sun, although astronomers still don’t know much else about it. The larger star — the one we see — is about two and a half times the Sun’s mass. It’s also a good bit wider than the Sun, and about 30 times brighter.
Perhaps the most interesting thing about the brighter star, though, is how fast it spins — more than a hundred times faster than the Sun. Astronomers calculate that it’s at about 89 percent of the speed needed to cause the star to break up. That dizzying spin pushes material at its equator outward. As a result, the star is about 20 percent fatter through its equator than through the poles.
Rasalhague is high in the southeast as darkness falls now. It’s fairly bright, so it’s easily visible to the unaided eye. It’s at the head of the classic stick figure that outlines Ophiuchus, which looks a bit like a coffee urn. Right now, that figure stretches to the right and lower right of Rasalhague as night falls, and below it in the wee hours of the morning.