See the moon near Castor and Pollux, October 17
The moon near Castor and Pollux October 17
On the mornings of October 17, 2022, the last quarter moon passes by the bright stars Castor and Pollux in the constellation Gemini the Twins. You’ll easily notice the bright stars Castor and Pollux because they are close together in the sky. Also, you may notice a brilliant star on the other side of the moon, that’s Procyon, or the Little Dog Star. It’s the brightest star in the constellation Canis Minor and the 8th brightest star in the sky.
To get a precise view from your location try Stellarium online.
The twin stars of Gemini: Castor and Pollux
Gemini is the constellation of the Twins, referring to the twins Castor and Pollux from Greek and Roman mythology. However, these two stars aren’t really twins. In fact, they’re quite different. Although Castor and Pollux appear close to each other, they’re not physically related or close to each other in space. Pollux is the closer star, and lies about 34 light-years away. While Castor resides at about 51 light-years distant.
When viewing the twin stars, you might notice Castor and Pollux are not the same brightness and color. Castor appears white and not as bright as Pollux. Yet Castor is listed as the alpha star in Gemini even though it’s the second brightest star in that constellation. On the other hand, Pollux shines brighter than Castor and is an orange star.
By the way, the color of a star is an indicator of its surface temperature. A white star is a relatively hot, young star, while an orange star is a cool star moving toward the end of its life.
So, Pollux’s orange color reveals that it’s a giant star. Pollux has a diameter of about 10 times that of our sun and is the closest giant star to Earth. It’s also one of the very few giant stars known to have an exoplanet.
Meanwhile, Castor is star system with six stars, consisting of three pairs of binary stars, all revolving around a common center of mass. You can even see Castor as two stars in a small telescope.
Bottom line: On the morning of October 17, 2022, look for the last quarter moon near Castor and Pollux, the twin stars of Gemini.
For more great observing events in the coming weeks, visit EarthSky’s night sky guide