2021, December 19-21:  Gemini Moon

December 19, 20, and 21, 2021:  The bright moon leading up to the winter solstice appears in the western sky before sunrise in front of Gemini.

2021, December 19, 20, and 21: The bright moon is in the western sky before sunup, in front of the Gemini Twins.
Image Caption – 2021, December 19, 20, and 21: The bright moon is in the western sky before sunup, in front of the Gemini Twins.

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by Jeffrey L. Hunt

The bright moon appears in the western sky before sunrise during the last three mornings before the winter solstice.  Each morning it is farther eastward and higher in the sky than the previous morning.

Here’s what to look for:

December 19:  One hour before sunrise, the bright moon, 100% illuminated, is about 15° up in the western sky at the feet of Gemini.  Technically, it’s still in Taurus, to the upper left of the Bull’s Horns, Elnath – also known as Beta Tauri – and Zeta Tauri.

In two mornings, the sun reaches the winter solstice, when it is farthest south of the celestial equator.  This morning the moon is near the sun’s summer solstice point.

At this hour, the moon is about 6 hours after the official Full moon phase.

The star cluster Messier 35 (M35) is 2.2° to the upper left of the lunar orb.  With the bright moon, certainly, this is not the morning to study the stellar bundle.  The moon’s spot helps us find the cluster.  Use a binocular.  Put the moon to the lower right portion of the field of view, the cluster appears near the center of the field.  Then move the moon out of the field leaving just the cluster.  Return earlier in the morning or later in the evening when the cluster is higher in the eastern sky.  Without the moon, the cluster looks like a tiny bunch of jewels on the dark velvet of the sky.

December 20: This morning the moon appears nearly full.  It’s 98% illuminated.  It is nearly 25° up in the sky and over 10° below Castor, one of the Twins.

December 21: The bright moon, about 95% illuminated and one-third of the way up in the western sky, is 3.2° to the lower left of Pollux, the other Twin.

With the moon this bright, it is necessary to use a binocular to see the dimmer starfield or to shield your eyes from the moon’s glare, as you would to block the sun.  Hold up and extend your hand.  Standing in the shadow of a house or building helps to see the dimmer stars as well.

Tomorrow morning the moon steps through Cancer, the dim region between Gemini and Leo.

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