Here’s our list of celestial events you’ll be able to see during the month of December. It will be an exciting month for viewing stunning planetary line-ups, a meteor shower, and the full Cold Moon. Be sure to bookmark this page and refer to it all month long!
Take note that we sometimes will use angular degrees to define the separation between two objects, such as (for example) a bright planet and the Moon. Keep in mind that the width of your clenched fist, held at arm’s length, measures roughly 10°.
When we speak of magnitude, we are referring to the brightness of an object, the lower the figure of magnitude, the brighter the object. The brightest stars are zero and first magnitude. Under a dark, clear sky, the faintest objects that you can see with just your eyes are fifth or sixth magnitude. Objects with negative magnitudes are the brightest. Sirius, the brightest star, is -1.4. Venus can get as bright as -4.8. A full Moon is -12.7 and the Sun is a blindingly bright -26.7!
All times are listed in Eastern Standard Time for the Northern Hemisphere.
December 2—Mars has been out of sight for many months now, but you can begin earnestly hunting for it during dawn. Binoculars are essential because Mars is faint and barely even clears the east-southeast horizon by mid-twilight, 45 minutes before sunrise. On December 2, look first for the slender sliver of the waning crescent Moon, and Mars will be situated about 7° to its lower left. If you see it, you are one of the select few catching the very start of a nearly two-year apparition during which the whole world will see Mars lighting the evening skies one year from now.
December 4—New Moon at 2:43 a.m. In this phase, the Moon is not illuminated by direct sunlight and is completely invisible to the naked eye.
The Moon is also at perigee, 221,701 miles away, its closest approach to Earth in 2021, which will result in an abnormally large range of tides for the next few days.
December 4th also marks the final eclipse of 2021; a total solar eclipse visible only from the icy continent of Antarctica. The path of totality, averaging 265 miles wide, will sweep inland south-southwest from the Weddell Sea, passing over Berkner Island and the Filchner-Ronne Ice Shelf, then continuing across West Antarctica, darkening the Executive Committee Range (a mountain range consisting of five major volcanoes), before moving offshore at the Ross Sea. For even the most ardent eclipse chaser, this will prove to be a tough assignment, although a few hardy souls did see the last total solar eclipse visible here (in 2003) from the ground, while others overflew this frozen land in commercial aircraft.
December 6—Shortly after sunset look low toward the southwest horizon for the eye-catching sight of a lovely crescent Moon hovering about 3½° below Venus. As the sky darkens, Venus seems to swell from a tiny white spark to a big, almost dazzling Christmas-season star; a glorious beacon, shining at its stunning maximum magnitude of -4.9 in early December.
Bright as it is, however, Venus remains fairly low at nightfall. You may have to move around to get a view past local obstructions. It starts the month setting 2 hours and 45 minutes after the Sun for viewers at latitude 40° north, though it’s only 20° high at sunset. But by the second half of December, it rapidly drops toward the horizon.
During this month its phase thins from 28% to 3% sunlit, while its diameter —the length of the crescent—dramatically increases in size. By New Year’s Eve, Venus sets 70 minutes after the Sun and has grown to 1/30 the apparent diameter of the Moon. The planet will go through inferior conjunction with the Sun on January 8, 2022.
December 7—Earliest sunset of 2021. Read more about it here.
December 7—Also, tonight the Moon will pay a visit to Saturn, passing about a half dozen degrees below it. But unlike last night, you’ll have to wait a little longer for the Moon’s companion to come out: Saturn is only about 1/175 as bright as Venus!
December 8—For the third night in a row, the Moon will pass underneath a bright planet. This time it’s Jupiter, which will be positioned about 8° to the upper left of the lunar crescent. Jupiter is still fairly high in the south-southwest at dusk and is very bright, shining at magnitude -2.2. If you’ve got a telescope, head out as early in the evening as possible before it sinks too low. By the end of the month, it sets as early as 8:45 p.m.
December 10—First Quarter Moon at 8:35 p.m. In this phase, the Moon looks like a half-Moon in the sky. One-half of the Moon is illuminated by direct sunlight while the illuminated part is increasing, on its way to becoming a full Moon.
December 13-14— The Geminid Meteor Shower, due to peak during the overnight hours, can produce as many as 60 to 120 slow, graceful shooting stars per hour under ideal conditions. They tend to be bright and appear yellow and have a reputation for occasional fireballs. Rates increase steadily for several days before maximum, then drop off quickly. The meteors that appear after maximum, however, tend to be especially bright. On the night of the Geminid peak this year, the Moon is three days past its first quarter phase, setting around 2:50 a.m. for mid-northern latitudes when the shower radiant (near the bright star Castor) appears almost overhead. That Tuesday morning, between moonset and dawn, the Geminids should put on a fine show. Bundle up!
December 18—December’s Full Cold Moon at 11:35 p.m. This full Moon is also called the Long Night’s Moon—a name doubly appropriate because the midwinter night is long and the Moon is above the horizon for a long time. It is the full Moon nearest to the winter solstice. It takes a high trajectory across the sky for those north of the equator. Check out our short video on how this Moon got its names!
December’s Full Moon
December 21—Winter Solstice at 10:59 a.m. The Sun reaches its southernmost point in the sky today and begins its six-month return northward, repeating its annual promise (for those living north of the equator) of another spring and summer to come. By convention, this moment marks the change of seasons—the beginning of winter in the Northern Hemisphere and summer in the Southern.
December 26—Last Quarter Moon at 9:23 p.m. In this phase, the Moon appears as a half Moon due to the direct sunlight; the illuminated part is decreasing toward the new Moon phase.
December 27—This morning, about an hour before sunrise, look low to the southeast horizon for the red 1st-magnitude star, Antares, and half as bright and hovering 4½° to its upper left will be Mars.
December 28—Mercury catapults up from the Sun’s afterglow to greet falling Venus in the last week of the month (and year). On December 21st, Mercury was still deep in the twilight glow 14° to Venus’s lower right—too low to be seen easily even with binoculars. However, this evening, Mercury shines conspicuously at magnitude -0.7, just 4° to the lower left of Venus. Both inner planets will comfortably fit in a standard field of 7-power binoculars.
December 31—On this final morning of 2021, early risers will see a waning crescent Moon form a triangle with Antares and Mars, low in the southeast dawn twilight.
By Farmers’ Almanac Astronomer Joe Rao. This calendar is adapted from “Skylog,” a regular feature appearing in Natural History magazine written by Mr. Rao since 1995.