The twins watching over, or watching out

SkyCaramba weekly astronomy blog for the week ending January 7, 2012

A pair of twins keeps watch over us all night during January. Castor and Pollux were seen as twins by the ancient Greeks and Babylonians. Together, their constellation is known as Gemini. The constellation is northeast of the easily recognized Orion.

The twins as they rise in the east

One legend says the twins are cattle thieves. One is rustling cattle from the Milky Way stream. The other, just outside the stream, is keeping watch for anyone who might catch them. A variant of that story says the twins went on a cattle raid with two cousins and the four got into a fight over splitting the spoils. One twin was killed. The other survived but begged to be with his brother. Their father Zeus put them in the stars.

Helen of Troy is the sister of Castor and Pollux according to the old stories. The twins joined Jason and the Argonauts in search of the Golden Fleece. Helping calm a terrible storm on that voyage, seafarers in real life over the centuries have considered Castor and Pollux their patron stars. They have been associated with St. Elmo’s Fire, a visible discharge of energy from ships’ masts when storms are near.

Castor is the star on the right (or to the west) representing the head of the twin by the same name. There are actually six stars tightly clustered in what the naked eye sees as a single point of light. Small to medium size telescopes should resolve it into two or three stars. The other stars are known because of their light patterns that can be detected with a spectroscope. That group is about 50 light years away.

The other star, Pollux, also representing a twin named for the star, is known to have a planet going around it. Pollux is about 35 light years from us.

The lower half of Gemini contains two similarly named stars. Mebsuta refers to a lion’s outstretched paw. Mekbuda to a lion’s folded paw. Both names are from an old Arabic account of what they represent.

In Chinese legend, Castor and Pollux are yin and yang. Those are two competing but balanced forces of nature.

Gemini has the distinction of being where Uranus and Pluto were when they were discovered. Uranus was near Propus in 1781 when William Herschel discovered it. Pluto was near Wasat in 1930 when Clyde Tombaugh found it.

One of the Messier objects, M35, is near Castor’s feet. You can see it with the naked eye. Use low magnification to see a better view with a telescope.

Here are some more web sites where you can find out more about Gemini and the stars in it.