Gemini is another zodiacal constellation, this one comprised of two guys, Pollux and Castor. Pollux is on the left, just like his star in the diagram above, while Castor is on the right. You may have heard the names Pollux and Castor before in movies, often as a code-name for twins. Those movie makers just aren't very original in their clever codes, are they. They never mention the other twins that go with Pollux and Castor, their twin sisters Helen (of Troy) and Clytemnestra. But that's mythology for you. Gemini is visible from winter through spring in the Iowa skys.