The constellation Gemini has two very bright stars called Castor and Pollux which, as it turns out, are the names of each twin the constellation represents. They are known as the Sons of Zeus because of the unusual circumstances of their birth.
As the story goes, there was a very beautiful Queen of Sparta known as Leda. One night, Zeus—the king of the gods—turned himself into a swan to visit Leda on the same night she had spent with her husband. These unions turned out to be quite fruitful and Leda subsequently gave birth to four children.
One set of children, Pollux and Helen (later to be known as Helen of Troy) were the children of Zeus. The other set of children, Castor and Clytemnestra were fathered by Leda’s husband, King Tyndareus. The children of Zeus were immortal, the children of Tyndareus were mortal.
Well, Castor and Pollux grew up the closest of friends, never fighting or acting without consulting each other. They looked alike and dressed alike.
Castor and Pollux had many adventures together—having joined the expedition of Jason and the Argonauts—until one day Castor—one of the mortal children—was run through with a sword and killed. Pollux grieved for his fallen brother and asked Zeus that the two should share immortality. And so Zeus placed them both in the sky as the constellation Gemini, where they are seen in close embrace, inseparable to this day.