What to See in the Night Sky for December 2021

A holiday comet, dueling meteor showers, and a remote total solar eclipse cap off the year.

Matterhorn with stars
coolbiere photograph / Getty Images

Santa's sleigh isn't even packed yet, but the December sky already has a few celestial gifts at the ready to close out 2021. So warm up your gloves by the fire, heat up the hot chocolate, and bundle up for a month of spectacular meteor showers, stargazing, a holiday comet from beyond the solar system, and the winter solstice.

Venus at its most glorious (Dec. 4)

Venus, Earth’s closest planetary neighbor, rings in the holiday season as the third brightest object in the sky after the sun and moon. On Dec. 4, the hottest planet in our solar system will reach its peak brilliance for the year, shining at a magnitude of -4.9. Look for it in the southwest during and after twilight. 

Penguins get a front-row seat for a total solar eclipse (Dec. 4)

On Dec. 4, penguins (and a few humans at remote research stations) will be treated to a total solar eclipse. While the path of totality (when the sun will be 100% blocked by the Moon) will take it across Antarctica, EarthSky reports that those in southernmost South America, Africa, Australia and New Zealand may catch a partial eclipse. 

Weather permitting, a view of the total solar eclipse from Union Glacier, Antarctica, will be streamed on YouTube and on nasa.gov/live. According to NASA, the stream starts at 1:30 a.m. EST, with totality beginning at 2:44 a.m. EST. 

Comet Leonard Makes a Holiday Flyby of Earth (Dec. 12) 

On the 12th day of Christmas, my true love gave to me...a glorious comet! That’s right, if you happened to miss Comet NEOWISE during the summer of 2020, Comet C/2021 A1—nicknamed Leonard—is shaping up to be a wonderful follow-up. The much-anticipated comet, which traveled an estimated 35,000 years from outside the solar system, will make its closest flyby of Earth (from a very comfortable 21 million miles away) on Dec. 12. In the days leading up to this event, the comet is expected to brighten—becoming visible with binoculars and possibly even the naked eye. 

To see Leonard, which is traveling at an exceptionally-fast 158,084 miles per hour relative to Earth, you’ll have a couple of options. On Dec. 10, about 30 minutes before sunrise, you’ll (hopefully) be able to spot it along the Eastern horizon, a few degrees beneath the bright star Arcturus. A few days later, on Dec. 17th, Leonard will appear just after sunset directly below Venus on the southwest horizon. 

Contemplate the mysterious Geminids meteor shower (Dec. 13-14)

One of the most prolific meteor showers of the year, with 120 to 160 shooting stars per hour, the Geminids are also one of the most scientifically perplexing. Whereas most meteor showers come from periodic comets shedding debris as they pass around the sun, the Geminids are apparently tied to an asteroid named 3200 Phaethon.

"Of all the debris streams Earth passes through every year, the Geminids' is by far the most massive," NASA astronomer Bill Cooke said in a statement. "When we add up the amount of dust in the Geminid stream, it outweighs other streams by factors of 5 to 500."

The problem is that the asteroid Phaethon simply isn't large enough to account for this massive collection of debris. In fact, even though it ejects some dust as it heats during its rendezvous with the sun, the expelled mass accounts for only 0.01% of the total Geminids debris stream. The only other explanation scientists can come up with is that Phaethon was once much larger and much more chaotic with the amount of debris it spewed into space.

"We just don't know," Cooke said. "Every new thing we learn about the Geminids seems to deepen the mystery."

To gaze upon this mystery for yourself, look up starting on the evening of Dec. 13 around 9 p.m. or 10 p.m. local time. The peak of the shower is expected at roughly 2 a.m. local time and, despite a waxing gibbous moon washing out the fainter meteors, should be visible through the rest of the week. For a more detailed rundown on what to expect and where to look, read our in-depth guide on how to watch the Geminid meteor shower.

Welcome the 'Cold Full Moon' (Dec. 18)

"The moon on the breast of the new-fallen snow, Gave a lustre of midday to objects below, When what to my wondering eyes did appear, But a miniature sleigh and eight tiny reindeer."

-'Twas the Night Before Christmas, Clement Clarke Moore

While the Old Farmer's Almanac referred to December's big lunar event as the Cold Full Moon, native people of North America also referred to it as the Big Spirit Moon, Blue Moon, and the Snow Moon. In New Zealand, where summer will soon officially kick off, this lunar season is described by the indigenous Māori as "Hakihea" or the "birds are now sitting in their nests."

View the Cold Moon in all its full-phase glory around 11:35 p.m. EDT.

The James Webb Space Telescope Finally Launches (Dec. 22)

In development since 1996 (when AOL.com was the most-visited website), the James Webb Space Telescope will finally launch later this month to begin its long-delayed mission of studying the heavens. According to NASA, the massive telescope will launch aboard Ariane flight VA256, with the earliest countdown beginning on Dec. 22. 

Once it reaches space, the Webb will take about a month to travel some 930,000 miles—well beyond the orbit of our Moon—and reside within a stable gravitational location known as a Lagrange point. Another six months of systems tests and careful unfolding of its 20-foot solar array will pass until it can begin its first observations. 

"It is the biggest, most powerful telescope ever to be put in space. There are big telescopes on the ground but nothing of this nature and complexity in space. Hands down, it's the most powerful thing out there," astrophysicist Blake Bullock told Treehugger

You can watch the launch live on NASA’s official website for the Webb—no AOL account required. 

Celebrate the winter solstice (Dec. 21)

The winter solstice, that brief moment when the sun is exactly over the Tropic of Capricorn, will take place on Dec. 21 at 10:58 a.m. EST.

While the winter solstice features the longest night of the year for those of us freezing in the Northern Hemisphere, it also brings with it the hope of more light in the days and months that follow. Because the sun is at its lowest arc in the sky, the 21st is also a time to get out and see extremely long shadows. "Your noontime shadow on the solstice is the longest it will be all year,"  Treehugger editorial director Melissa Breyer points out. "Relish those long legs while you can."

Catch the Ursids meteor shower (Dec. 21-22)

Despite having a tough act to follow after the spectacular Geminids, the annual Ursids meteor shower is still capable of throwing down up to 10 shooting stars per hour. Some years even surprise astronomers, with outbursts of 100 or more shooting stars per hour. For 2021, only the brightest will be visible, as light from a recently full Moon will wash out all but the brightest shooting stars. 

Originating from debris shed by Comet 8P/Tuttle, the Ursids appear to stream from the constellation Ursa Minor. Bundle up, get comfortable, and gaze up on the evening of the 21st or 22nd to catch the peak of this holiday shower.