Look up!

Kristen Lindquist: Get to know the constellation Gemini

Fri, 10/21/2016 - 12:00pm

The constellation Gemini, the Twins, is dominated by two bright stars side-by-side in the sky above Orion:  Castor and Pollux. These twin brothers share an interesting backstory in Greek mythology, one I've always remembered because it involves heteropaternal superfecundation — when two men father twins.

You may remember the story of Leda and the swan. As so often happened in the Greek myths, the god Zeus fell in love with the woman Leda and raped her while disguised as an animal, in this case a swan. As if that weren't strange and twisted enough, she ended up laying eggs which hatched into her sons Castor and Pollux. According to some versions of this myth, Pollux, the son of Zeus, was immortal, while Castor, the son of her husband King Tyndareus, was mortal. Be that as it may, the brothers were known by the Romans as the Dioscuri, a term that means "sons of Zeus."

And the brothers were inseparable in their adventures. Maritime buffs may know them as the protectors of ships and sailors who accompanied the hero Jason on his ship, Argo, when he sailed on his quest for the Golden Fleece. The ocean phenomenon St. Elmo's Fire was apparently associated with them, as well.

When Castor eventually died, Pollux asked his father, Zeus, if he could give half his immortality to Castor so that the two would be together forever. Thus they ended up next to each other in the night sky.

At our latitude here in coastal Maine, the constellation Gemini rises higher and higher throughout late fall into winter. The stars Castor and Pollux represent the heads of the twins (Castor being the higher of the two), from which two parallel lines of fairly visible stars stretch toward Orion to form their bodies.

The ancient Greeks and Romans weren't the only one to identify these two bright stars as a couple. Early Native Americans of the Klamath tribe also saw them as twins: a boy and a girl with a hunting bow. Other Native American stories recognized them as the archetypal twins representing the opposing duality of good and evil. Similarly, Chinese traditions marked them as Yin and Yang. Central Australian aboriginal culture had them pegged as twin creation deities in the form of lizards who helped put plants and animals in the world. Some early Christians saw them as Adam and Eve. Interestingly, ancient Arabians delineated them on early star charts as a pair of peacocks. Egyptians depicted them as two sprouting plants. Whatever they have been depicted as across the world and through time, they have always been a dynamic duo of some sort.

While paired for life in myths and stories, and of similar magnitude, the two stars couldn't be more different in reality. Castor is actually a complex star system over 50 light-years away that comprises three pairs of stars (three sets of twins!) orbiting around each other. Only one of the six stars is readily visible to the naked eye. The orange giant Pollux is a bit closer, about 34 light-years from the Sun, and technically the brighter of the two. The angle at which we see them creates the illusion that they are so close to each other in the sky.

The Geminid meteor shower, which appears to radiate from the vicinity of Castor and Pollux, occurs in mid-December each year. While this shower is typically a good one, producing about 100 meteors an hour, this year the full moon will obscure visibility during the shower's peak. But because the Geminids are known to be especially bright, astronomy sites are urging us to watch anyway.

Kristen Lindquist is an amateur naturalist and published poet who lives in her hometown of Camden.

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