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Gemini is known for its brightest stars, Pollux and Castor. They mark the heads of the mythological twins. The stars climb into view, in the east-northeast, by about 10 o’clock. Castor stands a bit above its brighter “twin.”
Gemini’s third-brightest star is at the bottom of the stick figure that outlines the twins — to the right of the twins as they rise. It’s easy to pick out, even under tonight’s full Moon. It represents one of the feet of Pollux.
Alhena is like many of the stars visible to the unaided eye. For one thing, it consists of two stars, not one. They’re so close together, though, that their light blurs into a single point. And for another, one of its stars is nearing the end of its life, so it’s especially big and bright. It’s this member of the duo that allows us to see Alhena, even though the system is more than a hundred light-years away.
This primary star is several times bigger and heavier than the Sun. It’s also later in life, so it’s puffing up to giant proportions. Right now, it shines more than a hundred times brighter than the Sun. Over millions of years, though, it’ll become even bigger and brighter.
Alhena’s other star is quite similar to the Sun — roughly the same size, brightness, and temperature. Since it’s less massive than its flashier companion, it’ll live billions of years longer. So it’ll still be shining steadily — if inconspicuously — long after the demise of its mate.
Tomorrow: a tough place to reach.
Script by Damond Benningfield