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Moon and Gemini on December 4 and 5

On December 4 and 5, 2017, a full-looking moon shines in front of the constellation Gemini the Twins, the radiant of the upcoming Geminid meteor shower. The Geminids are an annual shower, active from early to middle December. In 2017, the shower is expected to peak around December 12 and 13. Still, you might see a Geminid meteor or two tonight, despite tonight’s drenching moonlight.

Also, Gemini’s brightest stars, Castor and Pollux, will likely withstand tonight’s moonlit glare, as seen from most places.

If you can, pick out the star Castor. It’s near the radiant point of the Geminid meteor shower.

If you trace Geminid meteors backwards on the sky’s dome, you’ll see they come from an area of sky marked by the star Castor. Just remember … the meteors burn up in Earth’s atmosphere, roughly only about 60 miles (100 km) up. Meanwhile, Castor lies some 52 light-years away.

Look for the moon and Gemini stars to rise over your eastern horizon by mid-evening at mid-northern latitudes (and at a later hour from the Southern Hemisphere). Click here for recommended almanacs that’ll tell you the rising time of the moon in your sky. And to find out the rising times for Castor and Pollux (and other bright stars), click here.

The moon turned full on December 3, at 15:47 UTC; translate to your time zone. Converting UTC to U.S. time zones, that put the instant of the full moon at 10:47 a.m. EST, 9:47 a.m. CST, 8:47 a.m. MST and 7:47 a.m. PST on December 3. By the time you are reading this, full moon will likely have passed. Even so, the moon will look plenty full tonight, as it shines from early evening December 4 until dawn December 5.

By December 4, 2017, the moon was waning. Zefri Besar in Brunei Darussalam caught the December 4 moon near Castor and Pollux.

There’s another way to find the constellation Gemini, once the moon moves on. Are you familiar with Orion the Hunter, the gem of all constellations? If so, you can star-hop from Orion to the constellation Gemini on a dark, moonless night. As depicted in the sky chart below, draw an imaginary line from Mintaka, the westernmost star of Orion’s Belt, through the bright ruddy star Betelgeuse.

Star-hop to the constellation Gemini by drawing an imaginary line from Orion's Belt through the bright ruddy star Betelgeuse.

Star-hop to the constellation Gemini by drawing an imaginary line from Orion’s Belt through the bright ruddy star Betelgeuse.

At mid-northern latitudes, Orion and Gemnini rise at approximately the same time. At more southerly latitudes, like those in the Southern Hemisphere, Orion rises before Gemini. But no matter where you live worldwide – once the moon has moved to another part of the sky – Orion can serve as your ticket to locating the constellation Gemini the Twins.

Bottom line: The December 4, 2017 moon is in front of the constellation Gemini. Star-hop to Castor and Pollux – Gemini’s brightest stars – on this moonlit night. The star Castor is near the radiant point of the annual Geminid meteor shower.

Bruce McClure