The story behind the Gemini twins
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Published: December 14, 2005
Above red Betelgeuse in Orion are the Gemini twins, Castor and Pollux. Castor is the white, north-western one, Pollux, the brighter one, a beautiful golden orange.
That bright "star" about a hand-width to the east of Pollux is the planet Saturn.
In Greek mythology, that immortal philanderer, Zeus, was enamored by the mortal woman Leda. Though she was already married, Zeus came to her in the form of a swan. As a consequence, she gave birth to two eggs. Apparently nothing surprised the Greeks in those days.
In the first egg was the immortal child Pollux and his sister Helen (of Troy) in the second, the mortal child Castor and his sister Clytemnestra.
When Castor died, Pollux wished to be made mortal also, so he would not be separated from his brother, even in death. So moved were the gods by this great love, that they placed them in the sky together.
Of course, neither star will last forever. All stars eventually burn up their fuel and die. Of the two, Castor will die first. This is because hot stars die quickly. Castor is very hot, twice as hot as our sun. That's what its blue-white color tells us. So Castor is destined to be short-lived, lasting only a few hundred million years.
Pollux, though, will have a lifetime of more than 10 billion years. Its yellow-orange color tells us that it is a cool star, even cooler than our own Sun. It will burn for billions of years.
There's a consolation for Castor, of sorts. The Castor stellar system is one of the most complicated in the entire sky, consisting of six stars circling a common center. Castor, itself, is the brightest of the six. Pollux, like our own Sun, is solitary. How lonely by contrast.
Keep looking up!
"The Sky This Week" is written by Errol Pomerance. He runs Skyshows of Vermont, dedicated to bringing planetarium shows to Vermont schools. For information, call 325-3786. Visit his Web site for previous columns and show descriptions: www.sover.net/~skyshows. Have an astronomical question? E-mail skyshows@sover.net.
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