December 2025 Calendar

At any moment of the day, countless awe-inspiring celestial events are unfolding in the sky. With a universe of options, it can be hard to pin down what to observe. The purpose of this calendar is to provide a peek into what’s happening in the sky and in the world of astronomy in general and provide a quick list of highlights that can jump start your own explorations.

All Month: Christmas Tree Cluster

If you’re looking for a perfect sight for the holiday season, pop by the Monoceros constellation to visit the star-forming region NGC 2264 and explore the Christmas Tree Cluster. Located about 2,500 light-years away, this triangular collection of more than 600 young stars is about 30 light-years across and can be observed with binoculars or even the unaided eye under very dark skies. However, a small telescope will deliver the best views of this festive beauty. Other key highlights of NGC 2264 to check out while you are in the neighborhood are the 7-light-years-long Cone Nebula, the Snowflake Cluster and the Fox Fur Nebula.

Astrophotographer John Bellisario captured this image of the Christmas Tree Cluster and Cone Nebula with the aid of an Explore Scientific ED80 Triplet Refractor.

December 7 – Mercury at Greatest Western Elongation

On December 7, Mercury will be a bright presence in the pre-dawn sky as it moves into a prime position for early morning viewing. Because it is always so close to the Sun, Mercury is usually lost in its glare. But on this day it will be at its greatest western elongation or at its furthest point to the west of the Sun, which, means it will rise more than an hour before the Sun in some places. A clear sunrise horizon is essential for viewing Mercury, which can be found in the Libra constellation during the event.

December 7 – Puppid-Velid Meteor Shower Peaks

For meteor shower enthusiasts in the southern hemisphere, the fairly obscure Puppid-Velid meteor shower is expected to reach its peak around December 7th, resulting in five to 10 meteors per hour. Unfortunately, the peak comes on the heels of a Full Moon so even dedicated observers may struggle to catch much of a show.

December 13/14 – Geminid Meteor Shower Peaks

It’s once again time to grab your blanket and hunt out a patch of dark sky because one of the most prolific annual meteor showers is set to peak around December 14. First observed in the mid-1800s, the Geminid Meteor Shower has blossomed from meek beginnings and now produces more than 100 bright meteors - often yellowish in hue - per hour during its peak. It is not just the high activity that makes the Geminids notable. In fact, their origins make it truly unusual because instead of being generated by the debris left behind by a comet, they are caused by the asteroid 3200 Phaethon, which orbits the sun every 1.4 years. 3200 Phaethon has presented quite a puzzle for astronomers because it behaves like a comet - causing some to call it a “rock comet.”  Discovered in 1983, the odd asteroid is made of rock and not ice like a comet, but, like a comet, it has a highly elliptical orbit and emits dust, which leads to this meteor shower. Radiating from the Gemini constellation, the Geminids will be visible in both hemispheres.

December 21 – Solstice

Even if you can‘t make it to Stonehenge, you can still mark the December solstice on the 21st. At 15:03 Universal Time, the Sun will reach its southernmost point in the sky, which means the Northern Hemisphere will see its shortest day and longest night while the Southern Hemisphere enjoys its longest day and shortest night. For many, the event also unofficially marks the beginning of winter in the Northern Hemisphere and the start of summer in the Southern Hemisphere.

December 22 – Ursid Meteor Shower Peaks

Although it will not be as spectacular as the Geminids earlier in the month, the peak of the Ursids Meteor Shower is expected to occur in the wee hours of December 22nd. Long associated with debris from Comet 8P/Tuttle, the Ursids radiate from the Ursa Minor constellation and generate a maximum of about 10 meteors per hour during their peak time. This year the peak coincides with a New Moon, which is ideal for meteor hunting. If you can find a dark patch of sky free of light pollution, lie down on a blanket, look up and you might get lucky enough to see a nice show to end the year.

Astrophotographer John Bellisario captured this image of the California Nebula — a popular target in the Perseus constellation — with the aid of an Explore Scientific ED80 Triplet Refractor.

Constellation Spotlight: Perseus

Named for the hero in Greek mythology that slew Medusa, the Perseus Constellation stands strong in the northern hemisphere sky this time of year. Occupying an area of 615 square degrees, the constellation is visible in latitudes ranging from 90° North to 35° South and is famous for being the radiant point for the prolific Perseids meteor shower that peaks each year in mid-August. One of the most notable stars in the constellation is Algol, which is also known as the Demon Star. This famous star, which actually is a three-star system, is the first eclipsing binary star to be discovered. Observations of the stars that make up Algol eventually led to some major shake-ups in stellar evolution theory. Other sights to behold in Perseus are the Alpha Persei Cluster, which contains the constellation’s brightest star - the supergiant Mirfak (aka Alpha Persei); The Double Cluster, which is a pair of open clusters with a combined apparent magnitude of 4.3 that can be seen with the naked eye; and the Little Dumbell Nebula, a planetary nebula that is one of the most difficult objects to observe in the Messier catalogue. The constellation is also home to the California Nebula – a popular astrophotography subject. At about 100 lights years across, this emission nebula is huge, however, its low surface brightness means you will get the most detail with very dark skies, a rich field telescope and an H-Alpha filter.

WANT TO NAVIGATE THE NIGHT SKY WITH EASE? 

The Tirion Double-Sided Multi-Latitude Planisphere is a comprehensive sky map for northern hemisphere stargazers located between the equator and latitude 60° north that makes it easy to identify what constellations and major celestial objects are up in your night sky based on the date and time.

This night sky guide, which features maps crafted by noted celestial cartographer Wil Tirion, uses a double-sided design to minimize the distortion that is inherent to any polar-centered projection. This design choice means observers can see truer representations of the constellations located outside the equator (noted by a green line) by simply flipping the planisphere over.

In addition to showcasing constellations, this planisphere indicates the location of notable variable stars, open clusters, nebulae and galaxies. Other features include a line representing the ecliptic, a faint blue band for the Milky Way and a magnitude scale that indicates the brightness of the stars that are shown.  

This astronomy planisphere is made of durable plastic that easily wipes clean, and the rotating components are secured with sturdy brass rivets for smooth manipulation. Guidance for using your sky map is printed on the device for quick reference.