Gemini

February 08, 2019

Look high to the east in the evening and you’ll see two bright stars, one on top of the other. The top one is more blueish, and the bottom more yellow. That’s Castor and Pollux, respectively. The two stars that make up the heads of Gemini.

Castor and Pollux are of course the mythical twin brothers from the Greek legend, but let’s talk about the stars themselves.

First, Pollux. At just over 33 light years away, it’s the closest giant-stage star to our sun. A giant star is one that has depleted all of the hydrogen at its core and puffed up to many times its original size. Pollux also has a planet. One of the first exoplanets ever discovered… at more than twice the mass of Jupiter, it causes Pollux to wobble. The planet was first suspected in the early 90s when the wobble was first analyzed, and it was finally confirmed in 2006.

Now let’s look at Castor. What looks to the naked like a single star is actually a multiple star system of SIX stars in three binary pairs. Now, you can’t see all six from your backyard… but you can split the two brightest pairs with a small telescope. Just point your telescope right at the star and focus it until one star begins to look like two. And there you have it. Castor A and Castor B.

Splitting binary stars is a common hobby among amateur astronomers, and Castor is a great place to start. Again, look for Gemini high to the east in the evening. The later it is, the higher it will be. By 11 o’clock, it’ll be straight up.