FirstLight Astronomy Club

33°29.6'N / 117°06.8'W / 1190 ft.

Those Crazy Twins

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!

Uranus and Herschel

There was a day not that long ago when the only objects in the sky were the Sun, the Moon, the planets from Mercury to Saturn, and the stars. That was it. Those were all the animals in the celestial zoo.

Where were Uranus, Neptune, tiny Pluto and all those freakish things we have been learning about here over the years - galaxies, pulsars, quasars?

Their existence, in the eyes of humankind, was not known until the advent of a tiny tool we call the telescope, a tool that allowed us to spot these anomalies heretofore undetected by mere naked eye observation.

It was 227 years ago this week that the famed astronomer William Herschel, using a homemade telescope, doubled the distance to the borders of our solar system, extending it outward over another billion kilometers beyond Saturn. It was he who discovered Uranus, the seventh planet.

Usually I tell you where in the sky you can find the featured object. Sadly, Uranus at the moment is on the opposite side of the sun. That means it is now up only during the day, right next to our blazing star. To avoid a lawsuit I would recommend not looking for it. The resulting blindness would prevent you from finding it later this year when it claims the night skies once more.

As to its discoverer: William Frederick Herschel was born in Germany but in his teens took up residence in England. He, like many well-off gentlemen of his time, had a penchant for dabbling into the different disciplines. He was, for example, an accomplished musician. It was that an art that led him into the land of mathematics.

It was through math that he discovered the amazing world of astronomy. During this time, in his mid-thirties now, Herschel began constructing his first telescopes. He would end up making over 400 in his busy life.

When he was 43 years old, living in Bath, England, he discovered with his own telescope what he thought at first was a comet, but which shortly thereafter was shown to be a seventh planet, the first planet discovered since man was put here.
It had actually been seen before by other astronomers but was mistaken for a star. Herschel noticed in a series of observations that it moved just slightly, hence the initial thought that it might be a comet. But it turned out to be a far more distant heavenly body, a new planet.

Being a loyal Brit now, he named his newfound planet after his king, George III. Yes, the same George who gave the colonies in America so much grief.

Now, let's see how that new planet line-up might sound if the name had stuck: Mercury, Venus, Earth, Mars, Jupiter, Saturn, George. Hmmmm...

It was proposed by another astronomer that the planet should be named Herschel in his honor. Ahem. Thankfully, wiser, more traditional, minds prevailed, and the planet was named for the Greek god of the sky, Ouranos. Despite being more traditional, even that name broke ranks with the other planet names, being a Greek deity rather than a Roman one.

By the way, astronomers prefer to pronounce the planet's name with emphasis on the first syllable, not the second. It is not only preferred but can keep giggling to a minimum when you pronounce it in front of high schoolers. Trust me.

Herschel went on to do a lot more work in his life. He showed that gravity worked outside our solar system by keeping binary stars together. He built all those scopes, of course, some monstrous. He did some amazing studies with the Sun. And he would discover new moons around Saturn and George... uh... Uranus.

And he left behind a legacy, as his son John carried on the family tradition and became a famous astronomer himself.
But there was at least one more planet to be discovered! Alas, that’s a story for another day.

Until next time, clear skies!
Temecula Valley High School / Temecula, CA · Some images © Gemini Observatory/AURA Contact Me