The Skies of December 2020 by Dick Cookman

Highlights:  Comet Journal, Martian Landers, Meteor Showers, Planet Plotting, December Moon

Focus Constellations:  Ursa Major, Ursa Minor, Draco, Cygnus, Pegasus, Pisces, Andromeda, Cepheus, Cassiopeia, Perseus, Auriga, Taurus, Gemini, Orion, Camelopardalis

Comet Journals

Comet  88P/Howell (2020) is at 10th magnitude in Capricornus in early December. It will pass through the constellation in December and rapidly dim. It is a short period comet retreating to its outer asteroid belt aphelion. 

C/2020 S3 (Erasmus) is a predawn, 6th magnitude comet in Libra. It will move into Scorpius and will reach perihelion in Scorpius on the 12th when it may reach 5th magnitude. After dropping into the glare of sunrise as it passes through southern Ophiuchus, it will move between Sagittarius and Scutum in late December.

Comet C/2020 M3 (ATLAS) is at 8th magnitude in Taurus. It will move through Auriga in December and pass Capella at month’s end while dimming to 9th or 10th magnitude as it retreats from the inner Solar System. 

Mars Landers

David G. Horvath1, Pranabendu Moitra1, Christopher W. Hamilton1, Robert A. Craddock2, and Jeffrey C. Andrews-Hanna at the University of Arizona and the Smithsonian Institution submitted a paper last month with evidence suggesting a volcanic eruption occurred as recently as 53,000 years ago in a region called Cerberus Fossae. Up till now, most vulcanism was thought to be billions of years old, with minor eruptions until about 2.5 million years ago. The seismometer on the InSight Lander has recorded hundreds of small Marsquakes since April of 2019, some of which appear to have originated in the Cerberus Fossae region. The area displays a fissure surrounded by a 6 mile wide dark deposit thought to be composed of volcanic fragments including ash and dust. Such vulcanism can be attributed to a deep magma body which may be the heat source for occasional melting of ground ice which provides the liquid for carving some of the more recent valleys identified on Mars.        

Curiosity spent most of September and October drilling and sampling three drill holes at the Mary Anning clay rich rock outcrop on Mt. Sharp in Gale Crater. During the last week of October, the rover resumed its ascent of Mt. Sharp. The next target is the higher elevation Sulfate Unit which was first detected by orbiting satellites and is thought to represent an entirely new depositional environment. Ascent of the mountain is an ascent through time. The younger Sulfate Unit above Mary Anning may represent a much more arid time of evaporation of the lake that occupied Gale Crater and deposited the clays which formed the rocks found at Mary Anning.

Meteor Showers

December hosts 8 meteor showers, half gracing each hemisphere. Northern showers include the Chi Orionids, the Geminids, the Coma Berenicids, and the Ursids. Of the four, the Geminids are by far the best.

December 2: Chi Orionids. Active Nov 26-Dec 15. Radiant 05h28m +23°, ZHR 3. 28km/sec. Waning Gibbous Moon. Progenitors: Asteroid 2008XM1.

December 14: Geminids. Active Dec 7-Dec 17, Radiant 7h28m +33°, ZHR 120 variable, 35 km/sec. Waning Crescent Moon. Progenitor: Asteroid 3200 Phaethon.

December 20: Coma Berenicids. Active Dec 12-Jan 23, Radiant 11h40m +25°, ZHR 5, 65km/sec. Waxing Crescent Moon. Progenitor: Comet Lowe.

December 22: Ursids. Active Dec 17-Dec 26, Radiant 14h28m +76°, ZHR 10, up to 50+, 65km/sec. Waxing Gibbous Moon. Progenitor: Comet 8P/Tuttle.

Planet Plotting 

Next winter, observers will witness the Great Conjunction of Jupiter and Saturn in Capricornus when the two planets appear to be separated by only 0.1°, the closest approach between 1623 and 2080. On the 21st, Saturn appears so close to Jupiter that it actually joins the 4 Galilean moons of Jupiter. Next winter begins with the Winter Solstice which occurs at 5:02AM EST on the 21st. The Great Conjunction peaks 3 hours and 58 minutes later at 9:00AM EST. Some folks think that Great Conjunctions cause significant events. Similar close conjunctions of the two planets at the birth of Christ are one astronomical explanation for the Star of Bethlehem. The current confluence of the two events is driving the astrological community crazy. Some allude to the End Times and others claim it to be an entry into the Age of Aquarius. Astrologers place Capricorn in the sign of Aquarius, a mixup of constellations due to the precession of Earth’s axis which caused displacement of seasonal alignments of the Sun, Earth, planets, and constellations by one sign of the zodiac in the last 2000 years. 2000 years ago the Sun was in Aries on March 21st and now it is in Pisces, shifting all the seasonal lineups by one constellation. However, the universe doesn’t really care that the astrological community is 2000 years out of date.




Planet Passages



Sun Libra, Scorpius, Ophiuchus


New Moon 11:17AM EST 12/14
Mercury Libra, Ophiuchius, Sagittarius

-0.7 to -0.9

Superior Conjunction          10:00PM, EST 12/19
Venus Libra, Ophiuchus

-3.9 to -3.8

Mars Pisces

-1.1 to -0.2

Jupiter Sagittarius, Capricornus

-1.9 to -1.8

Saturn, 0.1°N 9:00AM EST 12/21
Saturn Sagittarius, Capricornus


Jupiter, 0.1°S 9:00AM EST 12/21
Uranus Aries


Neptune Aquarius

+7.9 to +7.9

The solstice occurs when Earth’s axis is tilted away from the Sun causing summer in the southern hemisphere because it receives more direct solar energy than delivered to the northern hemisphere by the oblique rays of the Sun which cause our winters with its short days and long nights. As the days start to lengthen for northerners after the solstice, holiday celebrations have been observed by cultures the world over throughout history. 

Jupiter (-1.9 to -1.8) and Saturn (+0.6) in Sagittarius and Capricorn in December are early evening planets in the southwestern sky. They set before 9:00PM EST on the 1st and about 7:30PM EST on the 31st. Neptune (+7.9) in Aquarius, Mars (-1.1 to -0.9) in Pisces, and Uranus (+5.7) in Aries are evening planets which set during the evening or slightly after midnight. Venus (-3.9 to -3.8) in Libra and Ophiuchus, and Mercury (-0.7 to -0.9) in Libra, Ophiuchus, and Sagittarius are visible before dawn in the eastern sky in early December and drop into the glow of dawn as the month progresses. After its conjunction with the Sun on the 19th, Mercury moves to the evening sky. 

The waning crescent Moon is within 0.8° of Venus at 4:00PM EST on the 12th and 1.0° from Mercury at Noon EST on the 14th. The waxing crescent Moon is 3.0° from Saturn at Midnight and 3.0° from Jupiter at 11:00PM EST on the 16th. It is 5.0° from Neptune at 3:00PMM EST on the 20th. The waxing gibbous Moon is 6.0° from Mars at 2:00PM EST on the 23rd, 3.0° from Uranus at 6:00PM EST on the 24th.

December Moon 

New Moon on December 14 at 11:17AM EST is the start of Lunation 1212 which ends 29.53 days later with January’s New Moon on the 13th at 12:00AM EST. New Moon brings a total solar eclipse to parts of Chile and Argentina. The Full Moon of December is on the 29th at 10:28PM EST. It is commonly known as the “Moon before Yule” or “Long Night” Moon. In colonial times, the December Moon was the “Christmas” Moon”. In Medieval England, the it was the “Oak Moon.” Celts named it the “Cold Moon” and the Chinese call it the “Bitter Moon”. Anishinaabe (Odawa and Ojibwe) people recognize it as “Manidoo-Giizisoons” (Little Spirit Moon). 

Lunar Perigee is on the 12th at 3:42PM EST when the Moon is 224,795 miles from Earth (56.72 Earth radii). Apogee (maximum orbital distance) is on December 24 at 11:31AM EST when the Moon’s distance is 251,663 miles (63.50 Earth radii).




Moon Passages

Moon Phase

Moon Age

Sun Ophiuchus


11:17AM EST, 12/14 New 0 days
Mercury Ophiuchus


1.0°NNE, Noon EST, 12/14 Waning Crescent 28.50 days
Venus Libra


0.8°N, 4:00PM EST, 12/12 Waning Crescent 26.66 days
Mars Pisces


6.0°S, 2:00PM EST, 12/23 Waxing Gibbous 9.11 days     
Jupiter Sagittarius


3.0°S, 11:00PM EST. 12/16 Waxing Crescent 1.99 days              
Saturn Capricornus


3.0°S, 12:00AM EST, 12/16 Waxing Crescent 2.61 days                
Uranus Aries


3.0°S, 6:00PM EST, 12/24 Waxing Gibbous 10.28 days
Neptune Aquarius


5.0°S, 3:00PM EST, 12/20 Waxing Crescent 6.15 days