Skylights: December 2025

December brings the longest nights, with the night of the 20th-21st giving us 11 hours 31 minutes of astronomical darkness, 12 hours 39 minutes outside of nautical twilight, 13 hours 47 minutes outside of civil twilight, and 14 hours 52 minutes between sundown and sunup.

The Sun

The earliest sunset of 2025 occurs at 4:14pm EST on the 8th.

Moving out of the non-zodiacal constellation Ophiuchus, the Sun moves into Sagittarius on the 18th, where it will spend the next 33 days.

The solstice occurs at 10:03am EST on the 21st. At this time, the Sun is at its most southerly declination of -23.44°. From now until June 21, the Sun will move northward, and length of daylight will be getting longer.

Simply by the cosmic coincidence of our solar system’s orientation within the Milky Way galaxy, the Sun appears to cross the galactic equator just nine hours and 12 minutes later.

The Moon

On the night before full Moon, the 3rd, the 98.7% gibbous Moon occults the Pleiades cluster.

The first of the bright stars to be occulted, Celaeno (16 Tauri), is occulted by the dark limb of the Moon at 8:33pm. This is followed by Electra (17 Tauri) at 8:45pm. Taygeta (19 Tau) goes behind the Moon six minutes later. At 9:04pm, Maia (19 Tau) is occulted. Finally, Asterope (21 Tauri) and 22 Tauri are occulted about 100 seconds apart, beginning at 9:14pm. The stars then reappear from the brightened limb of the Moon, beginning with Electra (9:15pm), Celaeno (9:41pm), Taygeta (10:02pm), Maia (10:12pm), Merope (10:25pm), followed by Asterope (10:25pm) and 22 Tau (10:29pm).

And while you’re watching the Moon pass in front of the northern sky’s most prominent star cluster, turn your gaze 4.1° to the south-southeast to find Uranus.

The full Cold Moon, the most northerly full Moon of 2025, occurs at 6:14pm on the 4th within Taurus. The Moon rises in the northeast at 3:38pm, 36 minutes before sunset. Full Moons that rise during daylight make some of the best photographs, so try to find a spot where you can watch it rise beyond some remarkable local scenery.

December’s full Moon also gives us one of the best opportunities for experiencing a feeling of daylight at night. With the Moon high in the sky, it occupies a position close to where the Sun lies around the June solstice, and with all the leaves down, the landscape is illuminated like no other time of the year. And if there is fresh snowfall, the effect is amplified into a dreamy nocturnal daylight, which is best experienced in an area away from artificial light. Nature organizations and recreation areas often conduct full Moon hikes, and this is the best time of year to experience one.

On the morning of the 5th, the full Moon sets in the northwest at 8:03am, over an hour after sunrise, presenting another photographic opportunity.

The Moon is a resident of the Winter Hexagon for the next three nights, and it partially crosses into the non-zodiacal constellation Auriga on the 6th.

On the 7th and 8th, the waning gibbous Moon is near Jupiter.

The 65.3% waning gibbous Moon joins Regulus early on the 10th, becoming as close as 0.2° to the east of the brightest star in Leo at 1:30am.

The Moon is last quarter in Leo, at 3:52pm on the 11th.

The 25% waning crescent Moon is 2.4° southwest of Spica on the 14th.

The 27-day old, 6.0% crescent Moon is located about 11° to the right of Mercury on the 17th.

An even older 28.2-day (38 hours before new) Moon is located 6.3° south of Mercury on the 18th. Turning a telescope on the thin 2.4% crescent will reveal Antares just 0.7° to the north of the Moon.

The 28.2-day (38 hours before new) Moon is located 6.3° south of Mercury on the 18th. Turning a telescope on the thin 2.4% crescent will reveal Antares just 0.7° to the north of the Moon.

The Moon is new at 8:43pm on the 19th, marking the beginning of Lunation 1274.

The wide waxing crescent Moon appears near Saturn on the 26th, and becomes first quarter at 2:10pm on the 27th, in Pisces.

The Moon again joins the Pleiades cluster early in the morning of the 31st, although we don’t get to see an occultation from New England this time. A quick look with binoculars will reveal the 86.1% gibbous Moon, the Pleiades, and magnitude 5.8 Uranus all within the same view. Uranus is 5.0° southeast of the Moon.

The Planets

Mercury is in the morning sky, and reaches its greatest elongation on the 7th, at 20.7° west of the Sun. Rising over 100 minutes before sunrise, early December is the best appearance of our innermost planet for 2025. It rises so early, that for the next two weeks it is above the horizon before the onset of astronomical twilight. This should give plenty of opportunity to spot the planet’s tiny globe go from crescent to gibbous, passing its 50% illuminated “half moon” phase on the 4th.

The innermost planet’s tiny gibbous globe lies 0.7° north of Acrab (beta Scorpii) on the 14th.

On the 17th, find Mercury 11.2° to the left and slightly below (east-northeast of) the 6.0% crescent Moon with its prominent Earthshine.

Mercury remains visible in the morning sky through the end of December.

Venus is low in the morning sky before sunrise, and is becoming difficult to observe.

Perhaps a trip to the beach on an exceptionally transparent early December morning will allow observers to spot the brilliant planet near its most distant point from Earth at about 1.7 au. To aid in locating it, look at the east-southeastern horizon at azimuth of 121°.

As it approaches its superior conjunction on January 6, Venus is too close to the Sun to be observed during the second half of December. It returns to our evening sky, becoming visible again, in February.

Mars sets within 30 minutes of sunset, and is too close to the Sun to observe during December. We won’t be able to easily observe Mars again until spring 2026.

Jupiter is moving retrograde in Gemini, and enhances the Winter Hexagon asterism by being positioned along the southeastern segment of the Winter Hexagon, crossing the line connecting Pollux and Procyon on the 3rd, and remaining close to this alignment all month.

The King of the Planets now shines at a brilliant magnitude -2.5, and rises into the early evening sky. It passes 0.1° to the north of the open star cluster NGC 2420 on the 16th and 17th.

By mid-month, Jupiter rises during evening twilight, and shines at a brilliant magnitude -2.5, becoming the most prominent starlike object in the evening sky. On the 22nd, it crosses the line connecting Pollux and Sirius.

Jupiter’s moons

Times EST, events filtered for visibility during dark hours from Seagrave Observatory

December 1-2: 20:14 - Europa exits occultation behind Jupiter; 23:57 - A close pairing of Europa and Ganymede to the east of Jupiter; 01:04 - Ganymede's shadow begins to cross Jupiter; 04:22 - Ganymede's shadow leaves Jupiter's disk; 04:38 - Ganymede begins transit of Jupiter. 2-3: 05:50 - Io's shadow begins to cross Jupiter; 06:44 - Io begins transit of Jupiter. 3-4: 21:32 - A very close pairing of Io and Europa to the west of Jupiter; 03:08 - Io enters eclipse by Jupiter's shadow; 06:18 - Io exits occultation behind Jupiter. 4-5: 00:18 - Io's shadow begins to cross Jupiter; 01:10 - Io begins transit of Jupiter; 02:36 - Io's shadow leaves Jupiter's disk; 03:26 - Io ends transit of Jupiter; 04:51 - Europa & Io in close pair to the east of Jupiter; 04:56 - Europa enters eclipse by Jupiter's shadow. 5-6: 21:38 - Io enters eclipse by Jupiter's shadow; 21:40 - Ganymede exits occultation behind Jupiter; 00:44 - Io exits occultation behind Jupiter.

December 6-7: 19:36 - Io begins transit of Jupiter; 19:41 - A pairing of Io and Callisto to the east of Jupiter; 21:04 - Io's shadow leaves Jupiter's disk; 21:52 - Io ends transit of Jupiter; 23:56 - Europa's shadow begins to cross Jupiter; 01:34 - Europa begins transit of Jupiter; 02:44 - Europa's shadow leaves Jupiter's disk; 04:22 - Europa ends transit of Jupiter. 7-8: 19:12 - Io exits occultation behind Jupiter; 21:34 - Callisto begins transit of Jupiter; 01:06 - Callisto ends transit of Jupiter; 03:16 - Io's shadow begins to cross Jupiter; 04:02 - Io begins transit of Jupiter. 8-9: 22:32 - Europa exits occultation behind Jupiter; 02:45 - Europa and Ganymede are paired to the east of Jupiter; 05:02 - Ganymede's shadow begins to cross Jupiter. 9-10: 02:46 A close pairing of Europa and Ganymede to the east of Jupiter. 10-11: 23:47 - Io and Europa are in a close pair to the west of Jupiter. Following this, the moons appear in order of orbital radius from the planet; 05:02 - Io enters eclipse by Jupiter's shadow. 11-12: 02:12 - Io's shadow begins to cross Jupiter; 02:56 - Io begins transit of Jupiter; 04:30 - Io's shadow leaves Jupiter's disk; 05:12 - Io ends transit of Jupiter, after which, the moons once again appear in order of orbital radius to the west of the planet. 12-13: 23:32 - Io enters eclipse by Jupiter's shadow; 01:04 - Ganymede exits occultation behind Jupiter; 02:30 - Io exits occultation behind Jupiter; 05:24 - Ganymede and Io make a close pair to the east of Jupiter.

December 13-14: 20:42 - Io's shadow begins to cross Jupiter; 21:22 - Io begins transit of Jupiter; 22:58 - Io's shadow leaves Jupiter's disk; 23:38 - Io ends transit of Jupiter; 02:32 - Europa's shadow begins to cross Jupiter; 03:52 - Europa begins transit of Jupiter; 05:20 - Europa's shadow leaves Jupiter's disk; 06:42 - Europa ends transit of Jupiter. 14-15: 20:56 - Io exits occultation behind Jupiter. 15-16: 19:00 - For much of the evening, Io, Europa and Calliso are in close arrangement to the west of Jupiter, forming a line and euqally spaced at 19:10; 20:48 - Europa enters eclipse by Jupiter's shadow; 21:30 - Callisto enters eclipse by Jupiter's shadow; 23:24 - Io, Callisto and Europa are in a tight grouping for several hours; 00:40 - Callisto exits eclipse by Jupiter's shadow; 00:50 - Europa exits occultation behind Jupiter; 03:08 - Callisto enters occultation behind Jupiter; 05:32 - Europa and Ganymede are paired to the est of Jupiter; 06:40 - Callisto exits occultation behind Jupiter. 16-17: None. 17-18: 19:50 - Europa ends transit of Jupiter; 01:51 - Io and Europa are in a close pair to the west of Jupiter; 06:58 - Io enters eclipse by Jupiter's shadow. 18-19: 04:06 - Io's shadow begins to cross Jupiter; 04:40 - Io begins transit of Jupiter; 06:22 - Io's shadow leaves Jupiter's disk; 06:56 - Io ends transit of Jupiter. 19-20: 22:56 - Ganymede enters eclipse by Jupiter's shadow; 01:26 - Io enters eclipse by Jupiter's shadow; 04:14 - Io exits occultation behind Jupiter; 04:24 - Ganymede exits occultation behind Jupiter.

December 20-21: 22:36 - Io's shadow begins to cross Jupiter; 13:06 - Io begins transit of Jupiter; 00:52 - Io's shadow leaves Jupiter's disk; 01:22 - Io ends transit of Jupiter; 05:08 - Europa's shadow begins to cross Jupiter; 06:08 - Europa begins transit of Jupiter. 21-22: 19:54 - Io enters eclipse by Jupiter's shadow; 21:49 - Europa and Io are in a close pair to the west of Jupiter; 22:40 - Io exits occultation behind Jupiter; 17:04 - Io's shadow begins to cross Jupiter; 17:32 - Io begins transit of Jupiter. 22-23: 19:20 - Io's shadow leaves Jupiter's disk; 19:48 - Io ends transit of Jupiter; 23:22 - Europa enters eclipse by Jupiter's shadow; 03:04 - Europa exits occultation behind Jupiter; 03:00 - Ganymede's shadow begins to cross Jupiter; 04:24 - Io enters eclipse by Jupiter's shadow. 23-24: 00:22 - Europa and Callisto are paired to the east of Jupiter. 24-25: 21:16 - Europa's shadow leaves Jupiter's disk; 22:06 - Europa ends transit of Jupiter; 03:47 - Europa, Callisto and Io are in a close grouping to the east of Jupiter, forming a line of equidistant spacing (Io, Europa, Callisto) at 04:39. 25-26: 19:17 - Ganymede and Io form a close pair to the west of Jupiter; 19:39 - Europa, Callisto and Ganymede are in a line of equidistant spacing to the west of Jupiter; 00:00 - Ganymede and Callisto are paired to the west of Jupiter; 06:00 - Io's shadow begins to cross Jupiter; 06:24 - Io begins transit of Jupiter. 26-27: 02:56 - Ganymede enters eclipse by Jupiter's shadow; 03:20 - Io enters eclipse by Jupiter's shadow; 05:58 - Io exits occultation behind Jupiter; 07:42 - Ganymede exits occultation behind Jupiter.

December 27-28: 20:43 - Ganymede and Europa are paired to the east of Jupiter; 00:30 - Io's shadow begins to cross Jupiter; 00:50 - Io begins transit of Jupiter; 02:46 - Io's shadow leaves Jupiter's disk; 03:06 - Io ends transit of Jupiter. 28-29: 21:50 - Io enters eclipse by Jupiter's shadow; 00:24 - Io exits occultation behind Jupiter. 29-30: 19:16 - Io begins transit of Jupiter; 21:14 - Io's shadow leaves Jupiter's disk; 21:32 - Io ends transit of Jupiter; 23:46 - Europa and Io are paired to the west of Jupiter; 01:58 - Europa enters eclipse by Jupiter's shadow; 05:18 - Europa exits occultation behind Jupiter. 30-31: 20:20 - Ganymede's shadow leaves Jupiter's disk; 21:24 - Ganymede ends transit of Jupiter. December 31-January 1: 21:04 - Europa's shadow begins to cross Jupiter; 21:32 - Europa begins transit of Jupiter; 23:52 - Europa's shadow leaves Jupiter's disk; 00:20 - Europa ends transit of Jupiter; 05:04 - Europa, Io and Callisto are in a close grouping to the west of Jupiter.

Saturn is high in the south during early evening hours. Its rings are still close to their narrowest inclination, remaining under 1° to our line of sight.

While we’re finished with Titan’s shadow transits for the season (until 2038), we still have transits, occultations, and eclipses of Saturn’s largest moon itself to watch. A transit is in progress as darkness falls on the 8th, and the moon emerges from Saturn’s eastern limb at about 6:35pm.

Titan emerges from occultation during twilight on the 16th. Another transit ends at 5:41pm on the 24th.

At mid-month, Saturn is high in the south at dusk, and sets before midnight. It reaches eastern quadrature on the 16th, which means the elongation angle between the Sun and Earth as seen by Saturn is at its greatest. Because of this, the shadows we see on Saturn and its rings are at their maximum, but because Saturn’s apparent ring tilt is still close to its minimum, this effect is greatly diminished than it is during times when the ring tilt is greater. Use a large telescope and high magnification under steady seeing conditions to look for an apparent gap on the rings just off the planet’s western limb. Early on the 16th, Titan will be just below this spot.

During the waning days of December, notice how Saturn is due south as twilight fades, making the best time to observe the ringed planet in the early evening, before it gets too low in the southwest.

Uranus continues to be well-positioned and easy to locate about 4.0° south of the Pleiades cluster in Taurus. During the first week of December, the magnitude 5.6, 3.8 arcsecond planet forms a line of equidistant spacing with the pair of 6th magnitude stars 13 and 14 Taur, to its west. It passes just 0.1° south of 14 Tauri, the easternmost of the pair, on the 13th and 14th.

Towards the end of December, the blue-green planet forms a triangle with 13 and 14 Tauri.

Neptune, like Saturn, is high in the south during early evening. Shining at magnitude 7.7 in Pisces, it can be seen within the same binocular field as the ringed planet, 4.3° to its northeast at the beginning of December, and closing to 3.5° to the northeast by month’s end.

The outermost planet reaches its stationary point on the 10th, resuming eastward (prograde) apparent motion thereafter. It sets before midnight by mid-December.

At the end of December, Neptune, as with Saturn, will be west of the meridian following twilight, signaling that their observing season has progressed beyond the halfway point. 

On the final evening of the year, Neptune will be 30 au away from Earth.

Minor Planets

Pluto is low in the southwest after sunset. It departs the evening sky too early to make observing the distant dwarf planet practical. It will remain mostly out of view until April.

Ceres, shining at magnitude 8.6, can be found just about 12° east-southeast of Saturn, and moving northeasterly through Cetus. In early December it is just 2.2° northeast of the magnitude 3.6 star iota Ceti.

In late December, the closest dwarf planet is now over 4.0° to the east-northeast of iota Ceti, but you can also use a pair of 6th magnitude stars, 12 and 13 Ceti, to locate it. These stars are 12° due east of Saturn (an equatorially mounted telescope needs only to be slewed in right ascension). From the easternmost star, move south and slightly west by 3.0° to find the magnitude 8.8 object.

4 Vesta is low in the southwest after sunset and will soon be out of view.

We don’t look for 433 Eros that often, but the Amor group asteroid happens to be located near the Andromeda Galaxy, Messier 31, during early December. It may be just beyond reach of binoculars, but a small telescope will show the magnitude 10.0 object arcing to the southwest of the galaxy, just over 2° from its core. 

Although classified as a near-Earth object, Eros is 0.398 au away on the 1st, and continues to move away from us. 

Events like this present a great opportunity to consider the scale of the universe. At this time, the Andromeda Galaxy is 400,000,000,000 times farther away than Eros. Using this ratio, placing the Andromeda Galaxy at the distance of the Moon, Eros would require a trip of a mere one millimeter. At this scale, Pluto would be no more than a hand’s width away.

Eros is the first asteroid to be orbited by a spacecraft, NASA’s Near Earth Asteroid Rendezvous (NEAR), which entered orbit around the asteroid in 2000. About a year later, the craft was renamed NEAR Shoemaker and, in another first, intentionally landed on the surface, despite the craft not being designed to do so. It continued sending signals back to Earth for about two weeks. Although it’s been silent for a quarter century, consider when you watch Eros sail past the Great Andromeda Galaxy that one of humanity’s explorers is part of that faint speck of light.

Asteroid 16 Psyche, the target object of NASA’s namesake mission that launched in 2023, reaches opposition on the 7th. Well-placed in Taurus a few degrees east of Aldebaran, the 280- kilometer-long asteroid shines as bright as magnitude 9.7 when it is at its closest distance of 1.685 au. On the 1st, it is 0.5° south of 104 Tauri, and 1.5° northwest of NGC 1817 and 1807, a pair of open clusters. On the 24th and 25th, it is 1.5° south of NGC 1647, another open cluster. The asteroid moves westward at about 0.2° per day towards the Hyades, and will appear to be associated with the cluster by the end of the month. 

The Psyche spacecraft will enter orbit around its asteroid in July 2029.

Meteors

The Geminids is one of the most favorable meteor showers of the year. Not only does this shower usually produce a consistent stream of up to 50 meteors per hour, northern hemisphere observers need not wait until the late hours for the radiant, located near Castor (alpha Geminorum), to rise above the horizon. These remnants of asteroid 3200 Phaethon enter the atmosphere at a modest 35 km/s.

On the heels of the prominent Geminids comes a little known meteor shower with the most northern radiant, the Ursids. Active from December 17th-26th, and peaking on the night of the 21st-22nd, these remnants from Comet 8P/Tuttle stream into our atmosphere at about 33 km/s and appear to radiate from a point near the bowl of the Little Dipper in the constellation Ursa Minor. The circumpolar location of this shower’s radiant gives patient observers the opportunity to see up to 5-10 meteors per hour throughout all hours of darkness, and in 2025, the nearly new Moon presents no interference

Stars & Constellations

In the early evening sky, we get our last views of Sagittarius and the southern sections of the summer Milky Way, the Big Dipper’s pointer stars, Dubhe (alpha) and Merak (beta), reach their lower culmination due north and below Polaris, and Pegasus’s Great Square is high in the south. The "loneliest star” Fomalhaut (alpha Piscis Austrini) is at its most prominent position, low in the south, as twilight fades on December evenings.

As the northern hemisphere enters its winter season, the Summer Triangle remains in the western sky for a diminishing number of hours. 

As the sky’s fifth brightest star, Vega, loses prominence in the west, the sixth brightest, Capella, rises higher in the east. As these two stars reach equal elevation in the early evening, this is a good time to observe their differing colors.

Vega is a type A0 main sequence star that shines with 36 times the luminosity of the Sun. Its rapid rotation causes an equatorial bulge, resulting in it being hotter at the poles than at the equator, radiating at 10100 Kelvin and 7900 Kelvin, respectively, and giving it a distinct blue-white appearance. It lies at a relatively close 25 light years from us. 

At 43 light years, the star we see as Capella (alpha Aurigae) is actually a pair of stars that orbit each other every 104 days. They are so close, however, as to be unresolvable in amateur telescopes, at just 50 milliarcseconds apart – a separation that corresponds to the distance of Venus from our Sun. Their spectral types are type G0 giant, and G8 giant, with corresponding temperatures of 4900 Kelvin and 5800 Kelvin, giving the system a yellow-white appearance in our sky. They shine with luminosities of 93 and 64 times that of the Sun.

Capella not only anchors the northern apex of the Winter Hexagon, it also lies close to the galactic equator, making this one of the most brilliant and object-rich regions of the sky for explorers using binoculars or telescopes. 

During the deepest hours of these long nights, the Winter Hexagon and its constellations Auriga, Taurus, Orion, Gemini, Canis Major, and Canis Minor, are prominently positioned high in the south.

Observers waiting for the Blaze Star, T Coronae Borealis, to brighten can see the Northern Crown constellation low in the northwest after sunset early in the month, but better viewing comes in the hours before morning twilight, when the constellation is fairly high in the east-northeast.

Lastly, skywatchers who have difficulty bearing the cold nights that will be with us for the next few months may feel somewhat relieved in anticipation for warmer nights by welcoming the stars of spring constellations such as Leo, Virgo, Hydra, and Corvus that populate the pre-dawn sky in December.