The two brightest stars of Gemini \u2014 Pollux and Castor \u2014 are in pretty good view in the east-northeast not long after the sky gets good and dark. Pollux is the brighter one, with Castor close above it. But Gemini is a big constellation, so it\u2019s a long way over to the third-brightest star, Alhena, which marks a foot of one of the twins. It\u2019s off to the right of the other two, by about twice the width of your fist held at arm\u2019s length.
\nAlhena consists of two stars. The star we see is about three times the Sun\u2019s mass and diameter. It\u2019s about 125 times brighter than the Sun. And it\u2019s thousands of degrees hotter. That makes it a \u201cclass A\u201d star.vb
\nAstronomers classify stars with the letters O-B-A-F-G-K-M. The classes are based on the surface temperatures of the stars. O stars are the hottest and bluest, while M stars are the coolest and reddest.
\nClass A stars are toward the top of the temperature scale. And they\u2019re not very common. They account for perhaps one percent of all stars in the galaxy. And Alhena is at the very top of the A stars \u2013 one of the hottest \u2013 so it shines pure white.
\nIts companion star has never been seen directly \u2013 it\u2019s too faint and too close to see through the glare of the brighter star. But instruments reveal some details. It\u2019s about the same mass as the Sun. It\u2019s probably in the same class as well \u2013 class G \u2014 the spot for yellow stars like the Sun and the unseen star of Alhena.
\xa0
Script by Damond Benningfield
\n\n