Supermoon greets December stargazers early

Published 10:34 am Saturday, November 25, 2017

By Deane Morrison, University of Minnesota

December wastes no time in giving us its best gift: a “supermoon.”

It shines the night of the 2nd to 3rd, with the moment of fullness at 9:47 a.m. on the 3rd. Just 17 hours later—at 2:46 a.m. on the 4th—the moon reaches perigee, its closest approach to Earth in a lunar cycle. This will be the closest full moon of the yeara. To see it at its biggest and roundest, check your local time of moonset for the morning of the 3rd and look to the west at least a half hour earlier.

Photo courtesy of the University of Minnesota

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This moon is known as both the full cold moon and the full long nights moon. Like other winter full moons, it enjoys a long, high ride across the night sky. This is because as the Northern Hemisphere tilts away from the sun in December, it tilts more toward the full moon, which is always on the other side of Earth. If you miss this supermoon, don’t worry; another is coming on New Year’s Day.

Jupiter is now starting to dominate the morning sky. Earth is gaining on Jupiter in the orbital race, and this widens the distance between the planet and the sun. But as it pulls away from the sun, Jupiter closes in on Mars, which appears as a reddish dot in the southeast. If Mars is hard to spot, look on Friday, the 15th, when bright Jupiter appears midway between a crescent moon and the red planet.

The gap between the two planets shrinks steadily throughout the month. On New Year’s Eve morning they’ll be just three degrees apart, and you’ll see a star between the two planets; this is Zubenelgenubi, in Libra, the scales. In early January, Zubenelgenubi and steadily climbing Jupiter will both make close passes by Mars.

In the evening sky, the familiar winter constellations are now making their grand entrance over the eastern horizon; all will be up by 10 p.m. Leading the way is the Pleiades star cluster, followed by, counter-clockwise from the top: Auriga, the charioteer; the Gemini twins Castor and Pollux; Canis Minor, the little dog; Canis Major, the big dog, which boasts Sirius, the brightest star in the night sky; Orion, the hunter; and Taurus, the bull.

No moon will interfere when the Geminid meteor shower peaks the night of the 13th to 14th. And at 10:28 a.m. on Thursday, the 21st, the winter solstice ushers in its namesake season. By then the sunsets will already be getting later; thus, even as the sun dips to its lowest point the seeds of spring will be germinating.

The University of Minnesota offers public viewings of the night sky at its Duluth and Twin Cities campuses. For more information and viewing schedules, see:
Duluth, Marshall W. Alworth Planetarium:
Twin Cities, Minnesota Institute for Astrophysics (during fall and spring semesters):
Check out the astronomy programs at the University of Minnesota’s Bell Museum ExploraDome: