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Dave Mitsky's Celestial Calendar for December 2020



December Celestial Calendar by Dave Mitsky


All times, unless otherwise noted, are UT (subtract five hours and, when appropriate, one calendar day for EST)


12/1   The Moon is at the ascending node (longitude 79.9 degrees) at 8:00

12/2   Mars is at the ascending node through the ecliptic plane at 3:00; the Moon is 0.2 degrees north of the bright open cluster M35 in Gemini at 8:00

12/3   The Moon is at its northernmost declination of the year (24.9 degrees) at 1:00; the Moon is 7.4 degrees south of the first-magnitude star Castor (Alpha Geminorum) at 21:00

12/4   The earliest end of evening twilight at 40 degrees north takes place today; the Moon is 3.7 degrees south of the first-magnitude star Pollux (Beta Geminorum) at 2:00

12/5   The Moon is 2.6 degrees north-northeast of the bright open cluster M44 (the Beehive Cluster or Praesepe) in Cancer at 4:00; Mercury is at the descending node through the ecliptic plane at 18:00

12/6   The Moon is 4.5 degrees north-northeast of the first-magnitude star Regulus (Alpha Leonis) at 20:00

12/7   The earliest sunset at latitude 40 degrees north occurs today; asteroid 16 Psyche (magnitude +9.5) is at opposition in Taurus at 20:00; the Moon is 0.5 degrees north of asteroid 4 Vesta, with an occultation taking place in Micronesia, the northern Philippines, Japan, most of China, most of Russia, and most of eastern and northern Europe, at 22:00

12/8   Last Quarter Moon occurs at 0:37; Mercury is 4.3 degrees north-northeast of the first magnitude star Antares (Alpha Scorpii) at 11:00; the Curtiss Cross, an X-shaped clair-obscure illumination effect located between the craters Parry and Gambart, is predicted to be visible at 16:32

12/12 The Moon is at perigee, subtending 33' 02" from a distance of 361,773 kilometers (224,795 miles), at 20:42; the Moon is 0.8 degrees north of Venus, with an occultation taking place in western North America, Alaska, Hawaii, and far eastern Russia, at 21:00

12/14 The peak of the Geminid meteor shower (a zenithal hourly rate of 100 to 120 per hour) occurs at 1:00; the Moon is at the descending node (longitude 260.0 degrees) at 11:00; the Moon is 1.0 degree north-northeast of Mercury at 12:00; a total solar eclipse visible from the South Pacific, southern South America, Antarctica, the South Atlantic, and southwestern Africa, begins at 14:33 UT1 and ends at 17:54 UT1; New Moon (lunation 1212) occurs at 16:16

12/15 The Moon is at its southernmost declination for the year (-24.9 degrees) at 22:00
12/16 Mercury is at aphelion (0.4667 astronomical units from the Sun) at 3:00

12/17 The Moon is 2.9 degrees south of Jupiter at 6:00; the Moon, Jupiter, and Saturn lie within a circle with a diameter of 3.0 degrees at 6:00; the Moon is 3.0 degrees southeast of Saturn at 7:00

12/18 The Sun enters the constellation of Sagittarius (ecliptic longitude 266.6 degrees) at 2:00

12/20 Mercury is at superior conjunction with the Sun (1.447 astronomical units from the Earth; latitude -4.5 degrees) at 3:00

12/21 The Moon is 4.2 degrees southeast of Neptune at 0:00; the Sun is at a longitude of 270 degrees at 10:02; the northern hemisphere winter solstice occurs at 10:02; Jupiter is 0.1 degrees south of Saturn at 14:00; First Quarter Moon occurs at 23:41

12/22 The Lunar X (Purbach or Werner Cross), an X-shaped illumination effect involving various rims and ridges between the craters La Caille, Blanchinus, and Purbach, is predicted to be fully formed at 4:33; the peak of the Ursid meteor shower (a zenithal hourly rate of 5 to 10 per hour) occurs at 9:00

12/23 Venus is 5.6 degrees north of Antares at 21:00

12/24 The Moon is 5.1 degrees southeast of Mars at 0:00; Mercury is at its southernmost declination (-25.1 degrees) at 7:00; the Moon is at apogee, subtending 29' 30" from a distance of 405,011 kilometers (251,663 miles), at 16:31; the equation of time is equal to zero at 22:00

12/25 The Moon is 3.2 degrees southeast of Uranus at 2:00

12/27 The Moon is 5.8 degrees southeast of the Pleiades at 2:00; the Moon is 4.6 degrees north of the first-magnitude star Aldebaran (Alpha Tauri) at 20:00

12/28 The Moon is at the ascending node (longitude 80.0 degrees) at 15:00

12/29 The Moon is 0.2 degrees north of M35 at 15:00

12/30 Full Moon (known as the Before Yule, Cold, Long Nights, and Oak Moon) occurs at 3:28

12/31 The Moon is 7.4 degrees south of Castor at 3:00; the Moon is 3.8 degrees south of Pollux at 8:00


Tycho Brahe, Johannes Kepler, Isaac Newton, E. E. Barnard, and Arthur Eddington were born in December.


Giovanni Cassini discovered the Saturnian satellite Rhea on December 23, 1672. Nicolas Louis de Lacaille discovered NGC 2070 (the Tarantula Nebula) on December 5, 1751. The bright spiral galaxies M81 and M82 in Ursa Major were discovered by Johann Bode on December 31, 1774. William Herschel discovered the galaxy pair NGC 3166 and NGC 3169 in Sextans on December 19, 1783. Caroline Herschel discovered Comet 35P/Herschel-Rigoliet on December 21, 1788. Caroline Herschel discovered Comet C/1791 X1 (Herschel) on December 15, 1791. The Jovian satellite Himalia was discovered by Charles Perrine on December 3, 1905. Audouin Dolfus discovered the Saturnian satellite Janus on December 15, 1966. The Saturnian satellite Epimetheus was discovered by Richard Walker on December 18, 1966.


The peak of Geminid meteor shower occurs on the morning of December 14th and is not adversely affected by moonlight. The Geminids, which are associated with the Palladian asteroid, or possible cometary nucleus, 3200 Phaethon, have become the most reliable meteor shower of the year. Geminid meteors appear to originate from a radiant that’s just northwest of Castor. That radiant lies almost at the zenith at 2:00 a.m. local time. Geminid meteors travel at a relatively slow speed of 35 kilometers per second (22 miles per second). An article on this year’s Geminids can be found on pages 14 through 19 of the December 2020 issue of Sky & Telescope. The Ursids, a normally minor meteor shower with a maximum zenithal hourly rate of 10 per hour, peak on the morning of December 23rd and are somewhat affected by the First Quarter Moon. The radiant is located close to Kochab (Beta Ursa Minoris), some 15 degrees from the north celestial pole. See for additional information on the Geminids and page 49 of the December 2020 issue of Sky & Telescope and for more on the Ursids. 


Information on passes of the ISS, the X-37B, the HST, Starlink, and other satellites can be found at


The Moon is 15.6 days old, is illuminated 99.8%, subtends 30.1 arc minutes, and is located in Taurus on December 1st at 0:00 UT. Due to the position of the ecliptic, the Moon reaches its highest point in the sky for the year in December. It attains its greatest northern declination for the month on December 3rd (+24.8 degrees) and December 30th (+24.8 degrees) and greatest southern declination (-24.9 degrees) on December 16th. Longitudinal libration is at a maximum of +6.5 degrees on December 19th. It’s at a minimum of -6.3 degrees on December 6th. Latitudinal libration is at a maximum of +6.9 degrees on December 21st and a minimum of -6.8 degrees on December 8th. Favorable librations for the following lunar features occur on the indicated dates: Crater Rydberg on December 6th, Crater Andersson on December 8th, Crater Vashakidze on December 18th, and Crater Compton on December 20th. New Moon occurs on December 14th. The Moon, Jupiter, and Saturn lie within a circle with a diameter of 3.0 degrees on December 17th. The Moon is at perigee (a distance of 56.72 Earth-radii) on December 12th and at apogee (a distance of 63.50 Earth-radii) on December 24th. The Moon occults asteroid 4 Vesta on December 7th and Venus on December 12th from certain parts of the world. Consult for information on lunar occultation events. Visit for tips on spotting extreme crescent Moons and for Full Moon data. Consult or download for current information on the Moon. Visit for a list of lunar maria and for a simple map of the Moon showing the most prominent maria. See for a lunar phase and libration calculator and,-27.218173,90,27.218173&proj=10&layers=NrBsFYBoAZIRnpEBmZcAsjYIHYFcAbAyAbwF8BdJUTBbSfI0yq8iioA for the Lunar Reconnaissance Orbiter Camera (LROC) Quickmap. Click on for a lunar phase calendar for this month. Times and dates for the lunar crater light rays predicted to occur this month are available at


The Sun is located in Scorpius on December 1st. Sol enters Sagittarius on December 18th. Winter solstice for the northern hemisphere occurs when the Sun is farthest south for the year on December 21st. It is the shortest "day" of the year (9 hours and 20 minutes) at latitude 40 degrees north. A total solar eclipse occurs in the southern hemisphere on December 14th. It’s the 23rd eclipse of Saros 142. Greatest eclipse takes place in southern Argentina at 16:13:29 UT1 and has a duration of 2 minutes 14 seconds. For more on this event, consult or pages 48 and 49 of the December 2020 issue of Sky & Telescope.


Brightness, apparent size, illumination, distance from the Earth in astronomical units (a.u.), and location data for the planets and Pluto on December 1st: Mercury (magnitude -0.8, 4.9", 96% illuminated, 1.37 a.u., Libra), Venus (magnitude -3.9, 11.7", 89% illuminated, 1.43 a.u., Libra), Mars (magnitude -1.1, 14.6", 92% illuminated, 0.64 a.u., Pisces), Jupiter (magnitude -2.0, 34.4", 100% illuminated, 5.73 a.u., Sagittarius), Saturn (magnitude +0.6, 15.7", 100% illuminated, 10.61 a.u., Sagittarius), Uranus (magnitude +5.7, 3.7", 100% illuminated, 19.10 a.u. on December 16th, Aries), Neptune (magnitude +7.9, 2.3", 100% illuminated, 30.02 a.u. on December 16th, Aquarius), and Pluto (magnitude +14.3, 0.1", 100% illuminated, 34.87 a.u. on December 16th, Sagittarius).


During the evening, Mars can be found in the southeast, Jupiter and Saturn in the southwest, Uranus in the east, and Neptune in the south. Mars and Uranus are in the west at midnight. In the morning, Mercury is located in the east and Venus in the southeast.


Mercury heads sunward and is not visible after early December. It's at aphelion on December 16th. The speediest planet achieves superior conjunction on December 20th.


Venus rises less than 90 minutes before the Sun by the end of the month. The separation between the planet and the Sun is 20 degrees on December 31st. A waning crescent Moon passes less than a degree north of Venus on December 12th. A daytime occultation of the planet that is discussed on page 50 of the December 2020 issue of Sky & Telescope takes place in some locations. Venus passes just 10 arc minutes north of the third-magnitude binary star Graffias (Beta Scorpii) on the morning of December 18th. The brightest planet enters Ophiuchus on December 22nd and lies 5.6 degrees north of Antares on the morning of December 23rd.


During December, Mars decreases in brightness from magnitude -1.1 to magnitude -0.3, in angular size from 14.6 arc seconds to 10.5 arc seconds, and in illumination from 92% to 89%. It culminates around 9:00 p.m. local time on December 1st and an hour earlier on December 31st. The Red Planet is at its ascending node on December 1st, crossing from south to north of the ecliptic. At 10:00 p.m. EST, Valles Marineris and the volcanoes of the Tharsis Ridge are well placed during the first half of the month. Followed by Sinus Sabaeus, Syrtis Major, and the Hellas basin during the middle of December. At month's end, Mare Cimmerium is centered on the Martian disk. The waxing gibbous Moon passes 5.1 degrees southeast of Mars on the evening of December 23rd.


Jupiter and Saturn are 2.1 degrees apart as December begins and lie within one degree of one another from December 12th through December 29th. During the first week of December, the two planets set by 8:30 p.m. local time. A waxing crescent Moon passes three degrees south of Jupiter and Saturn on the evening of December 16th. On December 21st, the two gas giants are separated by just six arc minutes less 45 minutes after sunset and are positioned about 14 degrees above the southwestern horizon some 30 degrees east of the Sun. On that date, Jupiter shines at magnitude -2.0 and subtends 33.3 arc seconds. Saturn's brightness is magnitude +0.6, its disk has an apparent diameter of 15.4 arc seconds, and its rings span some 35 arc seconds. This is the first conjunction of the two planets since 2000 and the closest conjunction since 1623. The last observable conjunction in which Jupiter and Saturn were closer occurred in 1226. During the conjunction, Ganymede will transit Jupiter. Saturn's satellites Enceladus, Tethys, Dione, and Titan will be to the west of the planet and Rhea and Mimas to the east. For additional information on this Great Conjunction, see and and


Uranus lies a few degrees southeast of the sixth-magnitude star 19 Arietis in southern Aries and transits the meridian in the early evening. Uranus lies five degrees northwest of the waxing gibbous Moon on December 24th. Visit or consult page 51 of the October 2020 issue of Sky & Telescope October for finder charts.


Neptune is located about three quarters of a degree northeast of the fourth-magnitude star Phi Aquarii during the early part of the month. As December ends, Neptune lies one degree from the star. The waxing crescent Moon passes four degrees south of Neptune on 20th. Neptune culminates during evening twilight and sets before midnight by the middle of the month. Browse or see page 48 of the September 2020 issue of Sky & Telescope for finder charts.


Finder charts for Uranus and Neptune are also available at and an article on observing the ice giants is posted at


Click on for JavaScript utilities that will illustrate the positions of the five brightest satellites of Uranus and the position of Triton, Neptune’s brightest satellite. 


Pluto will not be readily visible again until next year.


For more on the planets and how to locate them, see 


The graphic at displays the apparent and comparative sizes of the planets, along with their magnitudes and distances, for a given date and time.


The periodic comet 88P/Howell shines at approximately tenth magnitude as it heads northeastward through Capricornus this month. The comet passes about four degrees north of the seventh-magnitude globular cluster M30 on December 18th and approximately one degree southeast of Deneb Algedi (Delta Capricorni) on December 21st. For additional information on comets visible this month, browse and


A list of the closest approaches of comets to the Earth is posted at


Asteroid 1 Ceres heads northeastward through Aquarius during December, passing close to the eleventh-magnitude globular cluster NGC 7492 at the end of the month. Asteroids brighter than magnitude +11.0 reaching opposition this month include 16 Psyche (magnitude +9.5) on December 7th, 79 Eurynome (magnitude +9.9) on December 11th, 13 Egeria (magnitude +10.0) on December 20th, 39 Laetitia (magnitude +9.9) on December 21st, 52 Europa (magnitude +10.2) on December 28th, and 356 Liguria (magnitude +10.9) on December 31st. For information on this year’s bright asteroids and upcoming asteroid occultation events respectively, consult and


A wealth of current information on solar system celestial bodies is posted at and

Information on the celestial events transpiring each week can be found at and


The famous eclipsing variable star Algol (Beta Persei) is at a minimum, decreasing in brightness from magnitude +2.1 to magnitude +3.4, on December 3rd, 6th, 9th, 11th, 14th, 17th, 20th, 23rd, 26th, 29th, and 31st. Consult and page 50 of the December 2020 issue of Sky & Telescope for the times of the eclipses. Algol is at minimum brightness for observers in North America for about two hours centered at 1:54 a.m. on December 3rd, 10:43 p.m. EST on December 5th, 12:27 a.m. EST on December 26th, and at 9:16 p.m. EST on December 28th. The chance of seeing Algol at least one magnitude fainter than normal on a random night is about 1 in 30. For more on Algol, see and   


Free star charts for the month can be downloaded at and and


Data on current supernovae can be found at


Finder charts for the Messier objects and other deep-sky objects are posted at and and


Telrad finder charts for the Messier Catalog and the SAC’s 110 Best of the NGC are posted at and respectively.


Information pertaining to observing some of the more prominent Messier galaxies can be found at 


Author Phil Harrington offers an excellent freeware planetarium program for binocular observers known as TUBA (Touring the Universe through Binoculars Atlas), which also includes information on purchasing binoculars, at


Stellarium and Cartes du Ciel are useful freeware planetarium programs that are available at and


Deep-sky object list generators can be found at and and


Freeware sky atlases of varying "depth" can be downloaded at and and


One hundred and five binary and multiple stars for December: Gamma Andromedae, 59 Andromedae, Struve 245 (Andromeda); Struve 362, Struve 374, Struve 384, Struve 390, Struve 396, Struve 400, Struve 19, Otto Struve 67 (Camelopardalis); Struve 191, Struve Iota Cassiopeiae, Struve 263, Otto Struve 50, Struve 283, Struve 284 (Cassiopeia); 61 Ceti, Struve 218, Omicron Ceti, Struve 274, Nu Ceti, h3511, 84 Ceti, h3524, Lambda Ceti, Struve 330 (Cetus); h3527, h3533, Theta Eridani, Rho Eridani, Struve 341, h3548, h3565, Tau-4 Eridani, Struve 408, Struve 411, h3589, h3601, 30 Eridani, 32 Eridani (Eridanus); h3478, h3504, Omega Fornacis, Eta-2 Fornacis, Alpha Fornacis, See 25, Xi-3 Fornacis, h3596 (Fornax); Struve 268, Struve 270, h1123, Otto Struve 44, h2155, Nu Persei, Struve 297, Struve 301, Struve 304, Eta Persei, Struve 314, Otto Struve 48, Tau Persei, Struve 331, Struve 336, Es588, Struve 352, Struve 360, Struve 369, Struve 382, Struve 388, Struve 392, Struve 410, Struve 413, Struve 425, Otto Struve 59, Struve 426, 40 Persei, Struve 434, Struve 448, Es277, Zeta Persei, Struve 469, Epsilon Persei, Es878 (Perseus); Struve 399, Struve 406, Struve 401, Struve 422, Struve 430, Struve 427, Struve 435, 30 Tauri (Taurus); Epsilon Trianguli, Struve 219, Iota Trianguli, Struve 232, Struve 239, Struve 246, 10 Trianguli, Struve 269, h653, 15 Trianguli, Struve 285, Struve 286, Struve 310 (Triangulum)


Notable carbon star for December: U Camelopardalis


One hundred deep-sky objects for December: NGC 891 (Andromeda); IC 342, K6, St23, Tom 5 (Camelopardalis); Be65, IC 1848, K4, Mel15, NGC 896, NGC 1027, St2, Tr3 (Cassiopeia); M77, NGC 788, NGC 835, NGC 864, NGC 908, NGC 936, NGC 955, NGC 958, NGC 1015, NGC 1016, NGC 1022, NGC 1042, NGC 1052, NGC 1055, NGC 1087, NGC 1094 (Cetus); IC 2006, NGC 1084, NGC 1140, NGC 1187, NGC 1199, NGC 1209, NGC 1232, NGC 1291, NGC 1300, NGC 1309, NGC 1332, NGC 1337, NGC 1353, NGC 1357, NGC 1395, NGC 1400, NGC 1407, NGC 1421, NGC 1426, NGC 1440, NGC 1452, NGC 1453, NGC 1461 (Eridanus); NGC 1079, NGC 1097, NGC 1201, NGC 1292, NGC 1316 (Fornax I Galaxy Cluster), NGC 1317, NGC 1326, NGC 1344, NGC 1350, NGC 1360, NGC 1365, NGC 1371, NGC 1374, NGC 1379, NGC 1380, NGC 1381, NGC 1387, NGC 1398, NGC 1404, NGC 1406, NGC 1425 (Fornax); Bas10, Cz8, IC 351, IC 2003, K5, Mel 20, M34, NGC 869, NGC 884, NGC 957, NGC 1023, NGC 1058, NGC 1161, NGC 1245, NGC 1275 (Perseus I Galaxy Cluster), NGC 1333, NGC 1342, NGC 1444, Tr2 (Perseus); M45 (Taurus); NGC 777, NGC 784, NGC 890, NGC 925, NGC 949, NGC 959, NGC 978A/B (Triangulum)


Top ten binocular deep-sky objects for December: M34, M45, Mel15, Mel20, NGC 869, NGC 884, NGC 1027, NGC 1232, St2, St23


Top ten deep-sky objects for December: M34, M45, M77, NGC 869, NGC 884, NGC 891, NGC 1023, NGC 1232, NGC 1332, NGC 1360


Challenge deep-sky object for December: vdB14 (Camelopardalis)


The objects listed above are located between 2:00 and 4:00 hours of right ascension.