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The Dioscuri, Sons of Jove

Castor and Pollux, the twin stars of the constellation Gemini, while known as the Sons of Jove, should really have been called the Sons of Leda, for Jove was the father only of Pollux. Leda, wife of King Tyndareus of Sparta, was enticed by Jove, who had assumed the guise of a swan. Pollux, then, was immortal while his twin Castor, son of King Tyndareus, was mortal. The two were inseparable and devoted to each other. Castor became an accomplished equestrian, Pollux a champion boxer. Among other exploits, the twins were among the Argonauts in their quest for the golden fleece. At sea, a furious storm arose, such as the adventurers had never seen. To calm the crew, Orpheus began to play his harp as only he could bring out the enchanting music. As he played, he called upon the gods to save them, and miraculously the storm eased. At the same time twin stars appeared over the heads of Castor and Pollux. Thereafter the strange lights which sometimes appear during thunderstorms at sea, known as Saint Elmo's fire, were called by the names of the twins, and sailors and fishermen would pray to the twins in times of great peril. In China, the twin stars of Gemini were known as Yin and Yang, together the essence of the contrasts of the universe. Yin is feminine, water, darkness, winter, the Moon. Yang is male, fire, light and heat, summer, the Sun. Their symbol is two halves making up a complete circle. It is a symbol woven into all the religion and mythology-as well as the early science and philosophy-of China.

Other civilizations, too, had legends of these sky twins. Early Hebrews associated them with brothers Simeon and Levi. The Romans considered the two stars to be Romulus and Remus, the twin founders of Rome. In the American Northwest, the Klamath told of a boy and a girl who look down from the eastern horizon on December evenings over Crater Lake and make it freeze. But the stars Castor and Pollux are not identical twins. Pollux is somewhat brighter than Castor, at magnitude 1.16 compared to 1.6. Pollux is 35 light years distant from us, while Castor lies another 8 light years beyond. Pollux is a star many times the diameter of the Sun and 35 times as luminous. Castor is a multiple star system, consisting of three separate close pairs.

The constellation Gemini contains other double and multiple stars. Among these are Epsilon, a third magnitude star with a ninth-magnitude companion just under two arc minutes away. Eta Geminorum is outstanding. Its third-magnitude primary is a red-giant variable with a period of 233 days and a magnitude amplitude of about one. Another interesting star is the cepheid variable Zeta, with two companions. Two other doubles are Delta and 38 Geminorum, each pair exhibiting color contrasts. Deep sky objects in Gemini include the open cluster M35, which is on the edge of naked-eye visibility. Also, the enigmatic Eskimo or Clown Face planetary nebula, NGC 2392, is worthy of observation with small telescopes.

Gemini twins, Castor and Pollux, patron saints of sailors and fishermen

Eskimo Nebula, Jim Scala photo

Points of Light

When the late-evening Bay Area skies erupted in glowing color from an aurora borealis on March 30th, who did local all-news radio station KCBS contact for expert commentary on the matter? Why, they called the EAS's own Dave Rodrigues, whose explanations of the phenomenon were played hourly on its newscasts through the following morning.

San Francisco's Lakeside Kiwanis Club heard about our region's rich variety of sundials in a talk given by Carl Trost in April.

Atlas of the Lunar Terminator, by John Westfall, is one of several recently published guides to the Moon reviewed in the May issue of Sky and Telescope. ˜

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