Alhena

Gemini is known for its two brightest stars, which mark the heads of the mythological twins Pollux and Castor. The stars are low in the eastern sky in early evening, with Castor standing a bit above its “twin.” The constellation’s third-brightest star is at the bottom of the stick figure that outlines the twins. In fact, it represents one of the feet of Pollux. Alhena is like many of the stars that are 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 together to form 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.