Those Crazy Twins
Observing > Directly above your head in the evenings this week are two bright stars, twins as the legends go. They are Castor and Pollux, the Gemini dyads, twins from the days of myth.
Actually what you are looking at are their big, bright, hot heads. Castor’s is the bluer one, Pollux's star is a wee pinkish. Their skin-and-bones bodies trail off to the west making the starry duo's constellation appear, in toto, as a rectangle in the sky.
Their story is a typical ancient myth, filled with naughtiness and violence and escapade. One genesis of the Gemini goes something like this: There once was a princess named Leda who was of exceeding beauty. The big god of Olympus, Zeus, saw her beauty and to no one's surprise wanted her real bad. On her wedding night, when her husband was temporarily away, Zeus showed up disguised as a swan (don’t ask) and had his adulterous way with her. Her husband later consummated the marriage after Zeus flew the coop.
This was awkward to say the least, but the result was even more bizarre. She conceived two pairs of twins in a single, apparently very roomy egg. The one pair was immortal because of Zeus' contribution, the other pair mortal.
The boy from the immortal pair of twins was Pollux. Castor was his mortal half brother twin from the mortal side of the egg. The other kids apparently fell into relative anonymity.
The brothers ended up being as close as... well... brothers and shared a full life of boxing and soldiering and general horsing around. One of their fun times together included saving the Argo fleet from one nasty storm. This endeared them to sailors for centuries, and mariners would carve their likenesses into the bows of their ships for protection.
In their last caper together Castor got himself killed, much to the anguish and anger of both Pollux and Zeus. They dealt viciously with his attackers. Zeus afterwards saw that Pollux was deeply distraught and told him to come on up to Olympus. Pollux could get through the Olympic bouncers because his dad was Numero Uno. Castor, however, a mere mortal, was sent to the underworld. Well, this didn't sit well with Pollux – being a way from his brother – and he wheeled and dealed with Zeus until they worked out an agreement where the twins would spend alternating days above in Olympus and below in Hades.
In a poetic way we see that brotherhood in the skies today. Pollux descends below the western horizon almost immediately after Castor, and when they rise in the evening, there is Castor with his good brother Pollux right on his heels.
To astronomers these two stars have a real life of their own, but they are not twins, to be sure. Pollux is an older, redder, giant star, the brighter of the two. It is a lone star but just last year it was confirmed that there was a Jupiter-type planet in its grip.
Castor is another story altogether. Appearing as a single star to our eyeballs, it is "split" into a double star with any backyard telescope. It would be a nice play on the myth if it were just a twin binary, but observing the two with special instruments, it turns out each of those stars is itself a double star. These two sets of twins would be another nice lyrical ending to this sky story but there’s more!
It turns out there is a third, fainter star gravitationally bound to the first two sets of twins, and that that star itself has a twin, too. Sheesh!
That makes the Castor system a triple double system – six stars gravitationally bound, taking anywhere from days to centuries to go around each other in their heavenly dance. Twins everywhere!
Castor and Pollux are easy to spot, but if you cannot see them go out on the evening of April 12th when they and the first quarter Moon line up nicely like, well, triplets!
Until next time, clear skies!
Posted by Mark Ritter at 2008.03.23 02:49 PM | Comments (0)
