March's Constellation

This month look for the stars Castor and Pollux, the two brightest stars in Gemini the Twins. Since Castor (Alpha Geminorum) is a little fainter than Pollux (Beta Geminorum), Gemini is one of the few constellations in which the brightest star is not its alpha star. Caster is 52 light-years away and Pollux is 34 light-years away. If you were born in 1962 Castor is your birthday star this year and if you were born in 1980 Pollux is your birthday star this year.

Castor is an interesting star. Through a good telescope, it’s seen as two nearly identical stars with orbital periods of around 400 years. Currently, they are at their closest together with respect to Earth and the gap between them will widen over the coming decades. There’s a third much fainter companion to the south of the main pair that’s a red dwarf star called Castor C. Using spectroscopes, astronomers can detect the light of companion stars around all three stars. Therefore, Castor is reality three double stars in orbit around each other.

Gemini is nearly straight overhead by 8:30 PM at the beginning of March. Use binoculars or a small telescope to look for the galactic cluster M-35 in the right foot of Gemini. The galactic cluster appears as a small sprinkle of stars in binoculars and looks even better through a small telescope.