| December 4 | Mercury at Greatest Elongation |
| December 11 or 12 | Asteroid Leona passes in front of Betelgeuse |
| December 13 and 14 | Geminids Meteor Shower Predicted Peak |
| December 21 | Winter Solstice |
| December 22 and 23 | Ursids Meteor Shower Predicted Peak |
| December 26 | Full Cold Moon |
While those of us in the Northern Hemisphere are in the grips of the darkest days of the year, the colder and less humid air makes it a prime time for stargazing. Here’s what to look out for in the last month of 2023.
December 4 – Mercury at Greatest Elongation
The planet Mercury will be at its farthest from the sun at 12:26 a.m. EST on December 4. According to EarthSky, Mercury shines at magnitude -0.3 when it is at greatest elongation, or angular distance from the sun. This makes it brighter than most stars. It will be in front of the constellation Sagittarius the Archer, but most of the stars in this constellation will be lost in the twilight. For best viewing, look to the western sky shortly after sunset.
[Related: A probe destined for Mercury ended up rubbernecking Venus.]
December 11 or 12 Asteroid Leona passes in front of Betelgeuse
Betelgeuse is one of the sky’s biggest and brightest stars, but it will vanish for about 12 seconds as a large asteroid passes in front of it. Asteroid Leona will pass in front of the red supergiant star, temporarily blocking some of its light in a rare eclipse. With clear skies, should be visible to those along a narrow path stretching from Tajikistan and Armenia, westward towards Turkey, Greece, Italy, and Spain, across the Atlantic to Miami and the Florida Keys and parts of Mexico.
The timing and date will depend on where skygazers are located. In Cordoba Spain, the event will be at its midpoint at roughly 2:25 a.m. local time on December 12. In Miami, Florida it will be 8:24 p.m. local time on December 11. You can look up the exact time here.
December 13 and 14 – Geminids Meteor Shower Predicted Peak
If shooting stars are more your thing, you won’t want to miss this year’s Geminid meteor shower. This is one of the most reliable annual meteor showers. Stargazers may see up to 120 shooting stars per hour at the shower’s peak if they are watching from a dark location with clear skies.
The Geminids are predicted to peak on December 14. However, since the shower rises in mid-evening, the meteors should be active all night close to the peak dates of December 13 and 14. The young waxing crescent moon will also not interfere with the Geminids this year. The shower should start in mid-evening and be highest around 2 a.m.
December 21 – Winter Solstice
The first day of winter in the Northern Hemisphere is marked by the winter solstice. The solstice officially arrives on Thursday, December 21, 2023, at 10:27 p.m. EST.
Since the Earth is tilted on its axis, on the solstice, one half of the planet is pointed away from the sun and the other half is pointed towards it. The solstice technically only lasts a moment, when a hemisphere–in this case, the Northern–is tilted as far away from the sun as it can be.
[Related: What is a solstice? And other questions about the shortest day of the year, answered.]
The winter solstice is the shortest day of the year and those in the Northern Hemisphere will see the fewest hours of sunlight on the 21st. After the solstice, the days will continue to grow longer until we reach the summer solstice in June.
December 22 and 23 – Ursids Meteor Shower Predicted Peak
In case you miss Geminids, you won’t have to wait too long for another meteor shower. This year’s Ursid meteor shower is predicted to peak on December 21 and 22. According to EarthSky, Ursids is a little bit more low key than Geminids, but still worth checking out. It will also potentially overlap with the Geminids.
The first quarter moon may interfere with the Ursids this year, until the moon sets roughly three hours before the sunrise. However, the extra hours of darkness make it worth investigating. Under a clear sky, there can be about five to 10 meteors per hour. To catch the Ursids look towards the Little Dipper in the constellation Ursa Minor.
December 26 – Full Cold Moon
The last full moon of the year will appear full and bright on Christmas Day and will reach its peak illumination on December 26 at 7:33 p.m. EST. The moon’s disk will appear fully illuminated a few days before this, so you can start looking on December 24 and 25 as it rises. According to the Old Farmer’s Almanac, December’s full moon has a high trajectory in the sky. This means that it will be located above the horizon longer than most full moons.
December’s full moon is called the Cold Moon for the cold air that grips the Northern Hemisphere this time of year. Other names for December’s full moon include the Little Spirit Moon or Manidoo-Giizisoons in Anishinaabemowin (Ojibwe), the Storytelling Moon or Hiinaiwi Nuti in the Catawba Language of the Catawba Indian Nation in South Carolina, and the It’s a Long Night Moon or Wahsutes in Oneida.
The same skygazing rules that apply to pretty much all star gazing activities are key this month: Go to a dark spot away from the lights of a city or town and let your eyes adjust to the darkness for about a half an hour. Here’s to hoping for clear skies ahead!
Update, December 8, 2023, 8:39 a.m. This post has been updated to include Asteroid Leona passing in front of Betelgeuse.
