Moon near Castor and Pollux, December 9 and 10

Two positions of moon along green line of ecliptic near labeled Castor and Pollux.
Want to see Castor and Pollux, the twins in Gemini? Look for the moon near Castor and Pollux on the evenings of December 9 and 10, 2022. Chart via John Jardine Goss/ EarthSky.

Moon near Castor and Pollux

On the evenings of December 9 and 10, 2022, find the waning gibbous moon glowing near Castor and Pollux, the twin stars of Gemini. Although the twin stars don’t look alike, they are quite noticeable in the sky, because they’re bright and close together. However, Castor is slightly dimmer than Pollux.

Also nearby is Procyon, the brightest star in Canis Minor the Lesser Dog. Consequently, it’s sometimes called the Little Dog Star.

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A waning moon

The moon is just past full phase, now rising after sunset. On the 9th, the moon is inside the Winter Hexagon or Circle, a shape made of bright stars. The outline of the Winter Hexagon consists of six 1st-magnitude stars from different constellations. Pollux, being brighter than Castor, is the star from Gemini that marks one point in the Hexagon.

Then, on December 10, the moon, now down to 92% lit, is fairly close to Pollux. It lies near one of the edges of the Winter Hexagon. As the moon moves out of the way, it will become easier to see the shape of the Hexagon in a darker sky.

Castor and Pollux

Castor and Pollux may have the nickname of “twin” stars, but they’re not that much alike. Here are a few quick differences between Castor and Pollux.

First, Castor is 51 light-years away from us and is, in reality, 6 stars. Pollux is 34 light-years from Earth. Second, Castor shines with a whitish light tinged with blue, while Pollux is golden. Lastly, we know that Pollux has at least one planet, which scientists have named Thestias.

To see a precise view of the moon near Castor and Pollux from your location, try Stellarium Online.

Bottom line: See the moon near Castor and Pollux on December 9 and 10. Pollux is the brighter of the two twin stars in Gemini, and the moon will be closest to it on December 10.

For more great observing events in the coming weeks, visit EarthSky’s night sky guide

December 10, 2022

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Kelly Kizer Whitt

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