Gemini Rising

The twins of Gemini arc high across the sky on winter nights. Right now, the constellation is low in the east-northeast a couple of hours after sunset, but passes almost directly overhead not long after midnight.
The constellation is best known for the bright “heads” of the twins — the stars Pollux and Castor. Pollux is the brighter of the two, with slightly fainter Castor above it during the evening hours.
Both stars are impressive, but for different reasons.
Pollux is nearing the end of its life, so it’s puffed up to giant proportions. It’s many times wider than the Sun, and dozens of times brighter. Eventually, the nuclear reactions in its core will shut down, and its outer layers will puff out into space. Only the star’s hot but dead core will remain — a stellar remnant known as a white dwarf.
Castor is impressive not for its size, but for sheer numbers. What we see as Castor actually consists of at least six individual stars — one of the largest families of stars yet seen. These s