The “twin” stars of Gemini lead the Moon across the sky tonight. They stack up above the Moon at nightfall. Pollux, the brighter twin, is closer to the Moon.

Although Pollux and Castor are known as the twins, they actually represent only the heads of the two figures. The bodies of the twins are parallel to the horizon in early evening, stretching to the right of Pollux and Castor.

None of the other stars in Gemini’s classical outline is quite as bright as Pollux or Castor, but some of them are interesting anyway.

Several are giants — stars that have puffed up as they neared the ends of their lives. Others are binaries — two stars held close together by their mutual gravitational pull. And some are even more dramatic.

Delta Geminorum, which represents the pelvis of Pollux, is an example. It’s a triple star — three stars in a single system. The main star is beginning the transition from the prime of life to the giant stage. And the system has a place in astronomy history: In 1930, young astronomer Clyde Tombaugh discovered Pluto lurking near it.

Zeta Geminorum, the knee of Pollux, is a Cepheid variable. Once every 10 days or so, it puffs in and out like a beating heart. It’s huge and blindingly bright, and near the end of its life. It’s probably not quite massive enough to explode as a supernova, but no one knows for sure. Either way, its end is nigh — no more than a few million years away.
 

Script by Damond Benningfield

Support McDonald Observatory