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The third sign of the zodiac, Gemini, is easy to identify because its stars form an almost perfectly symmetric image in which one side mirrors the other, sort of a giant Rorschach test in the sky.
For obvious reasons, the Greeks decided that Gemini represented twin brothers. The two brightest stars of the constellation are named for each of the brothers. Alpha Geminorum is Castor, while beta Geminorum is called Pollux. According to Homer, Castor was an excellent horseman and his brother Pollux a soldier. When Castor was killed in some dispute, Pollux was so upset that he too wished to die so that he could remain with his brother. Zeus, being a fair god, worked out an acceptable compromise. They would spend half their time in heaven and half on Earth.
Half of thy time beneath the earth and half
Within the golden homes of heaven.
The twins were often regarded as protectors of sailors and represented by two stars over a ship. In the New Testament, a sea voyage is described on a "ship of Alexandria, with the Twin Brothers as figurehead."
Pollux has a particular deep shade of yellow compared to Castor’s whiteness. Don't be fooled by the Greek letters. Beta Geminorum, Pollux, is slightly brighter than alpha Geminorum, Castor.