Post by Dave Mitsky on Dec 11, 2021 6:25:11 GMT
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 5.3 degrees north-northeast of the first-magnitude star Spica (Alpha Virginis) at 4:00; Mercury is 3.7 degrees north-northeast of the first-magnitude star Antares (Alpha Scorpii) at 5:00; Neptune is stationary, with prograde or direct motion to begin, at 22:00
12/2 Mercury is at aphelion (0.4667 astronomical units from the Sun) today
12/3 The Moon is 0.7 degrees northeast of Mars at 2:00, with an occultation taking place in Hawaii, northern Polynesia, most of Micronesia, Japan, portions of eastern Russia, northeastern China, and most of Mongolia, at 0:00; Venus attains its greatest illuminated extent at 7:00; the Moon is at the descending node (longitude 241.8 degrees) at 15:00
12/4 The earliest end of evening twilight at 40 degrees north occurs today; the Moon is 3.8 degrees north-northeast of Antares at 5:00; a total solar eclipse visible from the South Orkney Islands and Antarctica begins at 5:29 and ends at 9:37; New Moon (lunation 1224) occurs at 7:43; the Moon is at perigee, subtending 33' 29" from a distance of 356,794 kilometers (221,702 miles), at 10:04; the Moon is 0.4 degrees east-southeast of Mercury at 14:00; Venus is at greatest brilliancy (magnitude -4.9) at 14:00
12/6 The Moon is at its southernmost declination for the year (-26.3 degrees) at 3:00; Mars and Uranus are at heliocentric opposition (longitudes 223.1 degrees and 43.1 degrees) at 11:00
12/7 The earliest sunset at latitude 40 degrees north occurs today; the Moon is 1.9 degrees southeast of Venus at 2:00
12/8 The Moon is 4.1 degrees southeast of Saturn at 4:00
12/9 The Moon is 4.2 degrees southeast of Jupiter at 10:00
12/10 The Moon displays maximum libration for the year (10.4 degrees) at 7:00; the Moon is 0.5 degrees north of the asteroid 2 Pallas, with an occultation taking place in parts of southeast Russia, most of Asia, India, the southern and eastern portions of the Middle East, the southern portion of the Arabian Peninsula, and central and eastern Africa, at 13:00; asteroid 44 Nysa (magnitude +9.1) is at opposition in Taurus at 14:00; a double Galilean shadow transit begins at 22:13
12/11 First Quarter Moon occurs at 1:35; the Moon is 3.9 degrees southeast of Neptune at 5:00; the Lunar X (Purbach or Werner Cross), an X-shaped clair-obscur illumination effect involving various rims and ridges between the craters La Caille, Blanchinus, and Purbach, is predicted to occur at 12:30
12/14 The peak of the Geminid meteor shower (a zenithal hourly rate of 120) is predicted to occur at 7:00
12/15 The Moon is 1.4 degrees southeast of Uranus at 8:00
12/16 Mercury is at its southernmost declination (-25.4 degrees) at 2:00; the Moon is 4.2 degrees southeast of the bright open cluster M45 (the Pleiades or Subaru) in Taurus at 23:00
12/17 The Moon is at the ascending node (longitude 61.7 degrees) at 0:00; the Moon is 6.2 degrees north-northwest of the first-magnitude star Aldebaran (Alpha Tauri) at 17:00
12/18 The Moon is at apogee, subtending 29' 25" from a distance of 406,320 kilometers (252,475 miles), at 2:15; the Sun enters Sagittarius (longitude 266.63 degrees on the ecliptic) at 9:00; Venus is stationary, with retrograde motion to begin, at 11:00
12/19 Full Moon occurs at 4:35; the Moon is 1.8 degrees north of the bright open cluster M35 in Gemini at 14:00; Mars is at the descending node through the ecliptic at 17:00
12/20 Venus is at the ascending node through the ecliptic plane at 8:00
12/21 The Moon is 6.2 degrees south of first-magnitude star Castor (Alpha Geminorum) at 5:00; the Moon is 2.6 degrees south of the first-magnitude star Pollux (Beta Geminorum) at 10:00; the northern hemisphere winter solstice occurs at 15:59; the longitude of the Sun is 270 degrees at 15:57
12/22 The Moon is 3.5 degrees north-northeast of the bright open cluster M44 (the Beehive Cluster or Praesepe) in Cancer at 13:00; the peak of the Ursid meteor shower (a zenithal hourly rate of 10) is predicted to occur at 16:00
12/23 Mercury is at its southernmost latitude from the ecliptic plane (-7.0 degrees) at 6:00
12/24 The Moon is 4.7 degrees north-northeast of the first-magnitude star Regulus (Alpha Leonis) at 9:00
12/25 The equation of time, which yields the difference between mean solar time and apparent solar time, is equal to 0 at 3:00
12/27 Last Quarter Moon occurs at 2:25; the Curtiss Cross, an X-shaped clair-obscur illumination effect located between the craters Parry and Gambart, is predicted to be visible at 15:14; Mars is 4.5 degrees north of Antares at 20:00
12/28 The Moon is 5.2 degrees north-northeast of the first-magnitude star Spica (Alpha Virginis) at 13:00
12/29 Mercury is 4.2 degrees south of Venus at 6:00
12/31 The Moon is at the descending node (longitude 241.2 degrees) at 1:00; the Moon is 0.9 degrees south of Mars, with an occultation taking place in the Falkland Islands, the southern tip of South America, the South Georgia Islands, Antarctica, Tasmania, and portions of southern Australia, at 20:00
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 adversely affected by moonlight until around 3:00 a.m. local time. 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 2021 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 affected by the light from a waning gibbous Moon. The radiant is located close to Kochab (Beta Ursa Minoris), some 15 degrees from the north celestial pole. See earthsky.org/space/everything-you-need-to-know-geminid-meteor-shower for additional information on the Geminids and page 49 of the December 2021 issue of Sky & Telescope and earthsky.org/?p=2976 for more on the Ursids.
Information on passes of the ISS, the X-37B, the HST, Starlink, and other satellites can be found at www.heavens-above.com/
The Moon is 25.9 days old, is illuminated 17.2%, subtends 32.1 arc minutes, and is located in Virgo 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 20th (+26.3 degrees) and greatest southern declination (-26.3 degrees) on December 6th. Longitudinal libration is at a maximum of +7.9 degrees on December 11th. It’s at a minimum of -7.1 degrees on December 27th. Latitudinal libration is at a maximum of +6.8 degrees on December 10th and a minimum of -6.7 degrees on December 24th. Favorable librations for the following lunar features occur on the indicated dates: Crater Bouvard R on December 1st, Crater Zeno on December 7th, Crater Vashakidze on December 10th, and Crater Graff on December 26th. New Moon occurs on December 4th. Large tides will take place in the following days. The Moon is at perigee (a distance of 55.94 Earth-radii) on December 4th and at apogee (a distance of 63.70 Earth-radii) on December 18th. The Moon occults Mars on December 3rd and December 31st and asteroid 2 Pallas on December 10th from certain parts of the world. Consult www.lunar-occultations.com/iota/iotandx.htm for information on lunar occultation events. Visit saberdoesthestars.wordpress.com/2011/07/05/saber-does-the-stars/ for tips on spotting extreme crescent Moons and www.curtrenz.com/moon06.html for Full Moon data. Consult time.unitarium.com/moon/where.html or download www.ap-i.net/avl/en/start for current information on the Moon. Visit www.fourmilab.ch/earthview/lunarform/maria.html?fbclid=IwAR0L-CYMauWi6Hhc09wUanCBQeDKNEw3gVJBHRwr0QEcodMJtNWK1OLMxYk for a list of lunar maria and upload.wikimedia.org/wikipedia/commons/thumb/3/36/Moon_names.jpg/600px-Moon_names.jpg?fbclid=IwAR1zUN--tW5jgxQPVOfp_6PpRtvXjprmsdrR531bAAjotCZImsof8HUNAKI for a simple map of the Moon showing the most prominent maria. See svs.gsfc.nasa.gov/4768 for a lunar phase and libration calculator and quickmap.lroc.asu.edu/?extent=-90,-27.218173,90,27.218173&proj=10&layers=NrBsFYBoAZIRnpEBmZcAsjYIHYFcAbAyAbwF8BdJUTBbSfI0yq8iioA for the Lunar Reconnaissance Orbiter Camera (LROC) Quickmap. Click on www.calendar-12.com/moon_calendar/2021/november 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 www.lunar-occultations.com/rlo/rays/rays.htm
The Sun is located in Ophiuchus 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 South Orkney Islands and Antarctica on December 4th. It’s the 13th eclipse of Saros 152. Greatest eclipse takes place at 07:33:28 UT1. For more on this event, consult www.eclipsewise.com/solar/SEprime/2001-2100/SE2021Dec04Tprime.html or pages 44 to 47 of the December 2021 issue of Astronomy.
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 -1.3, 4.6", 100% illuminated, 1.45 a.u., Ophiuchus), Venus (magnitude -4.9, 38.8", 29% illuminated, 0.43 a.u., Sagittarius), Mars (magnitude +1.6, 3.8", 99% illuminated, 2.49 a.u., Libra), Jupiter (magnitude -2.3, 38.4", 99% illuminated, 5.14 a.u., Capricornus), Saturn (magnitude +0.7, 16.0", 100% illuminated, 10.38 a.u., Capricornus), Uranus (magnitude +5.7, 3.7", 100% illuminated, 18.99 a.u. on December 16th, Aries), Neptune (magnitude +7.9, 2.3", 100% illuminated, 29.97 a.u. on December 16th, Aquarius), and Pluto (magnitude +14.3, 0.1", 100% illuminated, 35.09 a.u. on December 16th, Sagittarius).
During the evening, Mercury, Venus, and Saturn are in the southwest, Jupiter and Neptune are in the south, and Uranus is in the east. Uranus lies is in the west at midnight. In the morning, Mars is located in the southeast.
Mercury is at aphelion on December 2nd. It reaches its southernmost declination on December 16th and is at its greatest heliocentric latitude south on December 23rd. The speediest planet merges from the Sun's glare around December 25th. Mercury passes about four degrees south of Venus on the evening of December 28th.
As December begins, Venus shines at magnitude -4.9, subtends 38.8 arc seconds, and is illuminated 29%. By the end of the month, those figures have changed to magnitude -4.3, 60.4 arc seconds, and 3% as Venus nears inferior conjunction in January. Venus achieves greatest illuminated extent on December 3rd. The waning crescent Moon passes about two degrees north of Venus on the evening of December 6th. Venus is at the ascending node on December 20th.
Mars reappears in the morning sky in Libra, enters Scorpius in the middle of the month, and passes into Ophiuchus on December 25th. Mars and Uranus are at heliocentric opposition on December 6th. The Red Planet is at the descending node on December 16th. The waxing gibbous Moon lies within four degrees of Mars and Antares, the rival of Mars, on the evening of December 23rd. The waning gibbous Moon passes less than one degree north of Mars on December 2nd and less than one degree south of the planet on December 31st.
Jupiter drops in brightness from magnitude -2.3 to magnitude -2.1 and angular size from 38.4 arc seconds to 35.5 arc seconds during December. Jupiter and Saturn are a little more than 16 degrees apart on December 1st. The waxing crescent Moon passes some four degrees south of Jupiter on December 8th. A brief double Galilean shadow transit (Europa's shadow follows Callisto's) occurs on the evening of December 10th. The gas giant planet enters Aquarius on December 14th. Jupiter sets by 9:00 p.m. local time by December 31st. Information on Great Red Spot transit times and Galilean satellite events is available on pages 50 and 51 of the December 2021 issue of Sky & Telescope and online at www.skyandtelescope.com/observing/interactive-sky-watching-tools/ and www.projectpluto.com/jeve_grs
Saturn is quite low in the southwestern sky this month. The planet's disk subtends 16 degrees. Saturn's rings are inclined 19 degrees and span 35 degrees. The waxing crescent Moon passes four degrees south of the Ringed Planet on December 8th. Venus and Saturn are separated by 14 degrees on December 16th. Saturn sets not long after 7:00 p.m. local time on the final day of December.
Uranus lies some eleven degrees southeast of Hamal (Alpha Arietis). The waxing gibbous Moon passes less than two degrees south of Uranus on December 14th. Visit www.nakedeyeplanets.com/uranus.htm or consult page 51 of the October 2021 issue of Sky & Telescope for finder charts.
Neptune is located about three degrees northeast of the fourth-magnitude star Phi Aquarii on December 1st. As December ends, Neptune lies one degree from the star. The First Quarter Moon passes 4.5 degrees south of Neptune on December 10th. Browse www.nakedeyeplanets.com/neptune.htm or see page 48 of the September 2021 issue of Sky & Telescope for finder charts.
Finder charts for Uranus and Neptune are also available at skyandtelescope.org/wp-content/uploads/UranusNeptune2021_BW_WebFinder.pdf and an article on observing the ice giants is posted at skyandtelescope.org/observing/ice-giants-neptune-and-uranus/
Click on skyandtelescope.org/observing/interactive-sky-watching-tools/ 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 visible again until next year.
For more on the planets and how to locate them, see www.nakedeyeplanets.com/
The graphic at www.timeanddate.com/astronomy/planets/distance displays the apparent and comparative sizes of the planets, along with their magnitudes and distances, for a given date and time.
Comet C/2021A1 (Leonard), the brightest comet of the year, travels rapidly southeastward through Canes Venatici, Boötes, Serpens Caput, and Ophiuchus during the first part of December. It passes one degree to the east of the bright globular cluster M3 on the morning of December 3rd and some five degrees to the north of Arcturus on December 6th. The Earth will cross the orbital plane of Comet Leonard on December 8th. This comet may reach a peak brightness of fourth magnitude on December 12th when it passes within 0.23 astronomical units of the Earth and possibly first magnitude on December 14th due to forward scattering as a result of a phase angle of 160 degrees. However, there are signs that dust production has diminished and the comet may only reach second magnitude as a result. Comet Leonard enters the evening sky on December 12th and may be potentially visible to mid-northern observers around December 14 or December 15th. It passes five degrees below Venus on the evening of December 17th and within 2.6 million miles of that planet on December 18th. The speedy comet will attain an altitude of about five degrees above the southwestern horizon on December 22nd. An article on Comet Leonard appears on pages 48 and 49 of the December 2021 issue of Sky & Telescope. Other comets brighter than tenth magnitude include C/2019 L3 (ATLAS), 19P/Borrelly, and 67P/Churyumov-Gerasimenko. For additional information on comets visible this month, browse cometchasing.skyhound.com/ and www.aerith.net/comet/future-n.html and cobs.si/
A list of the closest approaches of comets to the Earth is posted at www.cometography.com/nearcomet.html
Asteroid 1 Ceres shines at seventh magnitude as it heads northwestward through Taurus this month. Asteroid 44 Nysa (magnitude +9.1) is at opposition in Taurus on December 10th. For information on this year’s bright asteroids and upcoming asteroid occultation events respectively, consult curtrenz.com/asteroids.html and asteroidoccultation.com/
A wealth of current information on solar system celestial bodies is posted at nineplanets.org/ and www.curtrenz.com/astronomy.html
Information on the celestial events transpiring each week can be found at astronomy.com/skythisweek and www.skyandtelescope.com/observing/sky-at-a-glance/
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 2nd, 5th, 8th, 11th, 13th, 16th, 19th, 22nd, 25th, 28th, and 31st. Consult www.skyandtelescope.com/observing/interactive-sky-watching-tools/ and page 50 of the December 2021 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 2:49 a.m. EST on December 4th, 11:38 p.m. EST on December 7th, 8:27 p.m. EST on December 10th, 1:22 a.m. EST on December 27th, and 10:11 p.m. EST December 30th. 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 stars.astro.illinois.edu/sow/Algol.html and www.solstation.com/stars2/algol3.htm
Free star charts for the month can be downloaded at www.skymaps.com/downloads.html and www.telescope.com/content.jsp?pageName=Monthly-Star-Chart and whatsouttonight.com/
Data on current supernovae can be found at www.rochesterastronomy.org/snimages/
Finder charts for the Messier objects and other deep-sky objects are posted at freestarcharts.com/messier and freestarcharts.com/ngc-ic and www.cambridge.org/turnleft/seasonal_skies_october-december
Telrad finder charts for the Messier Catalog and the SAC’s 110 Best of the NGC are posted at www.custerobservatory.org/docs/messier2.pdf and sao64.free.fr/observations/catalogues/cataloguesac.pdf respectively.
Information pertaining to observing some of the more prominent Messier galaxies can be found at www.cloudynights.com/topic/358295-how-to-locate-some-of-the-major-messier-galaxies-and-helpful-advice-for-novice-amateur-astronomers/
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 www.philharrington.net/tuba.htm
Stellarium and Cartes du Ciel are useful freeware planetarium programs that are available at stellarium.org/ and www.ap-i.net/skychart/en/start
Deep-sky object list generators can be found at www.virtualcolony.com/sac/ and tonightssky.com/MainPage.php and telescopius.com/
Freeware sky atlases of varying "depth" can be downloaded at www.deepskywatch.com/deep-sky-hunter-atlas.html and www.olle-eriksson.com/night-sky-maps/ and allans-stuff.com/takis-8-5-magnitude-star-atlas/
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.
All times, unless otherwise noted, are UT (subtract five hours and, when appropriate, one calendar day for EST)
12/1 The Moon is 5.3 degrees north-northeast of the first-magnitude star Spica (Alpha Virginis) at 4:00; Mercury is 3.7 degrees north-northeast of the first-magnitude star Antares (Alpha Scorpii) at 5:00; Neptune is stationary, with prograde or direct motion to begin, at 22:00
12/2 Mercury is at aphelion (0.4667 astronomical units from the Sun) today
12/3 The Moon is 0.7 degrees northeast of Mars at 2:00, with an occultation taking place in Hawaii, northern Polynesia, most of Micronesia, Japan, portions of eastern Russia, northeastern China, and most of Mongolia, at 0:00; Venus attains its greatest illuminated extent at 7:00; the Moon is at the descending node (longitude 241.8 degrees) at 15:00
12/4 The earliest end of evening twilight at 40 degrees north occurs today; the Moon is 3.8 degrees north-northeast of Antares at 5:00; a total solar eclipse visible from the South Orkney Islands and Antarctica begins at 5:29 and ends at 9:37; New Moon (lunation 1224) occurs at 7:43; the Moon is at perigee, subtending 33' 29" from a distance of 356,794 kilometers (221,702 miles), at 10:04; the Moon is 0.4 degrees east-southeast of Mercury at 14:00; Venus is at greatest brilliancy (magnitude -4.9) at 14:00
12/6 The Moon is at its southernmost declination for the year (-26.3 degrees) at 3:00; Mars and Uranus are at heliocentric opposition (longitudes 223.1 degrees and 43.1 degrees) at 11:00
12/7 The earliest sunset at latitude 40 degrees north occurs today; the Moon is 1.9 degrees southeast of Venus at 2:00
12/8 The Moon is 4.1 degrees southeast of Saturn at 4:00
12/9 The Moon is 4.2 degrees southeast of Jupiter at 10:00
12/10 The Moon displays maximum libration for the year (10.4 degrees) at 7:00; the Moon is 0.5 degrees north of the asteroid 2 Pallas, with an occultation taking place in parts of southeast Russia, most of Asia, India, the southern and eastern portions of the Middle East, the southern portion of the Arabian Peninsula, and central and eastern Africa, at 13:00; asteroid 44 Nysa (magnitude +9.1) is at opposition in Taurus at 14:00; a double Galilean shadow transit begins at 22:13
12/11 First Quarter Moon occurs at 1:35; the Moon is 3.9 degrees southeast of Neptune at 5:00; the Lunar X (Purbach or Werner Cross), an X-shaped clair-obscur illumination effect involving various rims and ridges between the craters La Caille, Blanchinus, and Purbach, is predicted to occur at 12:30
12/14 The peak of the Geminid meteor shower (a zenithal hourly rate of 120) is predicted to occur at 7:00
12/15 The Moon is 1.4 degrees southeast of Uranus at 8:00
12/16 Mercury is at its southernmost declination (-25.4 degrees) at 2:00; the Moon is 4.2 degrees southeast of the bright open cluster M45 (the Pleiades or Subaru) in Taurus at 23:00
12/17 The Moon is at the ascending node (longitude 61.7 degrees) at 0:00; the Moon is 6.2 degrees north-northwest of the first-magnitude star Aldebaran (Alpha Tauri) at 17:00
12/18 The Moon is at apogee, subtending 29' 25" from a distance of 406,320 kilometers (252,475 miles), at 2:15; the Sun enters Sagittarius (longitude 266.63 degrees on the ecliptic) at 9:00; Venus is stationary, with retrograde motion to begin, at 11:00
12/19 Full Moon occurs at 4:35; the Moon is 1.8 degrees north of the bright open cluster M35 in Gemini at 14:00; Mars is at the descending node through the ecliptic at 17:00
12/20 Venus is at the ascending node through the ecliptic plane at 8:00
12/21 The Moon is 6.2 degrees south of first-magnitude star Castor (Alpha Geminorum) at 5:00; the Moon is 2.6 degrees south of the first-magnitude star Pollux (Beta Geminorum) at 10:00; the northern hemisphere winter solstice occurs at 15:59; the longitude of the Sun is 270 degrees at 15:57
12/22 The Moon is 3.5 degrees north-northeast of the bright open cluster M44 (the Beehive Cluster or Praesepe) in Cancer at 13:00; the peak of the Ursid meteor shower (a zenithal hourly rate of 10) is predicted to occur at 16:00
12/23 Mercury is at its southernmost latitude from the ecliptic plane (-7.0 degrees) at 6:00
12/24 The Moon is 4.7 degrees north-northeast of the first-magnitude star Regulus (Alpha Leonis) at 9:00
12/25 The equation of time, which yields the difference between mean solar time and apparent solar time, is equal to 0 at 3:00
12/27 Last Quarter Moon occurs at 2:25; the Curtiss Cross, an X-shaped clair-obscur illumination effect located between the craters Parry and Gambart, is predicted to be visible at 15:14; Mars is 4.5 degrees north of Antares at 20:00
12/28 The Moon is 5.2 degrees north-northeast of the first-magnitude star Spica (Alpha Virginis) at 13:00
12/29 Mercury is 4.2 degrees south of Venus at 6:00
12/31 The Moon is at the descending node (longitude 241.2 degrees) at 1:00; the Moon is 0.9 degrees south of Mars, with an occultation taking place in the Falkland Islands, the southern tip of South America, the South Georgia Islands, Antarctica, Tasmania, and portions of southern Australia, at 20:00
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 adversely affected by moonlight until around 3:00 a.m. local time. 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 2021 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 affected by the light from a waning gibbous Moon. The radiant is located close to Kochab (Beta Ursa Minoris), some 15 degrees from the north celestial pole. See earthsky.org/space/everything-you-need-to-know-geminid-meteor-shower for additional information on the Geminids and page 49 of the December 2021 issue of Sky & Telescope and earthsky.org/?p=2976 for more on the Ursids.
Information on passes of the ISS, the X-37B, the HST, Starlink, and other satellites can be found at www.heavens-above.com/
The Moon is 25.9 days old, is illuminated 17.2%, subtends 32.1 arc minutes, and is located in Virgo 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 20th (+26.3 degrees) and greatest southern declination (-26.3 degrees) on December 6th. Longitudinal libration is at a maximum of +7.9 degrees on December 11th. It’s at a minimum of -7.1 degrees on December 27th. Latitudinal libration is at a maximum of +6.8 degrees on December 10th and a minimum of -6.7 degrees on December 24th. Favorable librations for the following lunar features occur on the indicated dates: Crater Bouvard R on December 1st, Crater Zeno on December 7th, Crater Vashakidze on December 10th, and Crater Graff on December 26th. New Moon occurs on December 4th. Large tides will take place in the following days. The Moon is at perigee (a distance of 55.94 Earth-radii) on December 4th and at apogee (a distance of 63.70 Earth-radii) on December 18th. The Moon occults Mars on December 3rd and December 31st and asteroid 2 Pallas on December 10th from certain parts of the world. Consult www.lunar-occultations.com/iota/iotandx.htm for information on lunar occultation events. Visit saberdoesthestars.wordpress.com/2011/07/05/saber-does-the-stars/ for tips on spotting extreme crescent Moons and www.curtrenz.com/moon06.html for Full Moon data. Consult time.unitarium.com/moon/where.html or download www.ap-i.net/avl/en/start for current information on the Moon. Visit www.fourmilab.ch/earthview/lunarform/maria.html?fbclid=IwAR0L-CYMauWi6Hhc09wUanCBQeDKNEw3gVJBHRwr0QEcodMJtNWK1OLMxYk for a list of lunar maria and upload.wikimedia.org/wikipedia/commons/thumb/3/36/Moon_names.jpg/600px-Moon_names.jpg?fbclid=IwAR1zUN--tW5jgxQPVOfp_6PpRtvXjprmsdrR531bAAjotCZImsof8HUNAKI for a simple map of the Moon showing the most prominent maria. See svs.gsfc.nasa.gov/4768 for a lunar phase and libration calculator and quickmap.lroc.asu.edu/?extent=-90,-27.218173,90,27.218173&proj=10&layers=NrBsFYBoAZIRnpEBmZcAsjYIHYFcAbAyAbwF8BdJUTBbSfI0yq8iioA for the Lunar Reconnaissance Orbiter Camera (LROC) Quickmap. Click on www.calendar-12.com/moon_calendar/2021/november 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 www.lunar-occultations.com/rlo/rays/rays.htm
The Sun is located in Ophiuchus 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 South Orkney Islands and Antarctica on December 4th. It’s the 13th eclipse of Saros 152. Greatest eclipse takes place at 07:33:28 UT1. For more on this event, consult www.eclipsewise.com/solar/SEprime/2001-2100/SE2021Dec04Tprime.html or pages 44 to 47 of the December 2021 issue of Astronomy.
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 -1.3, 4.6", 100% illuminated, 1.45 a.u., Ophiuchus), Venus (magnitude -4.9, 38.8", 29% illuminated, 0.43 a.u., Sagittarius), Mars (magnitude +1.6, 3.8", 99% illuminated, 2.49 a.u., Libra), Jupiter (magnitude -2.3, 38.4", 99% illuminated, 5.14 a.u., Capricornus), Saturn (magnitude +0.7, 16.0", 100% illuminated, 10.38 a.u., Capricornus), Uranus (magnitude +5.7, 3.7", 100% illuminated, 18.99 a.u. on December 16th, Aries), Neptune (magnitude +7.9, 2.3", 100% illuminated, 29.97 a.u. on December 16th, Aquarius), and Pluto (magnitude +14.3, 0.1", 100% illuminated, 35.09 a.u. on December 16th, Sagittarius).
During the evening, Mercury, Venus, and Saturn are in the southwest, Jupiter and Neptune are in the south, and Uranus is in the east. Uranus lies is in the west at midnight. In the morning, Mars is located in the southeast.
Mercury is at aphelion on December 2nd. It reaches its southernmost declination on December 16th and is at its greatest heliocentric latitude south on December 23rd. The speediest planet merges from the Sun's glare around December 25th. Mercury passes about four degrees south of Venus on the evening of December 28th.
As December begins, Venus shines at magnitude -4.9, subtends 38.8 arc seconds, and is illuminated 29%. By the end of the month, those figures have changed to magnitude -4.3, 60.4 arc seconds, and 3% as Venus nears inferior conjunction in January. Venus achieves greatest illuminated extent on December 3rd. The waning crescent Moon passes about two degrees north of Venus on the evening of December 6th. Venus is at the ascending node on December 20th.
Mars reappears in the morning sky in Libra, enters Scorpius in the middle of the month, and passes into Ophiuchus on December 25th. Mars and Uranus are at heliocentric opposition on December 6th. The Red Planet is at the descending node on December 16th. The waxing gibbous Moon lies within four degrees of Mars and Antares, the rival of Mars, on the evening of December 23rd. The waning gibbous Moon passes less than one degree north of Mars on December 2nd and less than one degree south of the planet on December 31st.
Jupiter drops in brightness from magnitude -2.3 to magnitude -2.1 and angular size from 38.4 arc seconds to 35.5 arc seconds during December. Jupiter and Saturn are a little more than 16 degrees apart on December 1st. The waxing crescent Moon passes some four degrees south of Jupiter on December 8th. A brief double Galilean shadow transit (Europa's shadow follows Callisto's) occurs on the evening of December 10th. The gas giant planet enters Aquarius on December 14th. Jupiter sets by 9:00 p.m. local time by December 31st. Information on Great Red Spot transit times and Galilean satellite events is available on pages 50 and 51 of the December 2021 issue of Sky & Telescope and online at www.skyandtelescope.com/observing/interactive-sky-watching-tools/ and www.projectpluto.com/jeve_grs
Saturn is quite low in the southwestern sky this month. The planet's disk subtends 16 degrees. Saturn's rings are inclined 19 degrees and span 35 degrees. The waxing crescent Moon passes four degrees south of the Ringed Planet on December 8th. Venus and Saturn are separated by 14 degrees on December 16th. Saturn sets not long after 7:00 p.m. local time on the final day of December.
Uranus lies some eleven degrees southeast of Hamal (Alpha Arietis). The waxing gibbous Moon passes less than two degrees south of Uranus on December 14th. Visit www.nakedeyeplanets.com/uranus.htm or consult page 51 of the October 2021 issue of Sky & Telescope for finder charts.
Neptune is located about three degrees northeast of the fourth-magnitude star Phi Aquarii on December 1st. As December ends, Neptune lies one degree from the star. The First Quarter Moon passes 4.5 degrees south of Neptune on December 10th. Browse www.nakedeyeplanets.com/neptune.htm or see page 48 of the September 2021 issue of Sky & Telescope for finder charts.
Finder charts for Uranus and Neptune are also available at skyandtelescope.org/wp-content/uploads/UranusNeptune2021_BW_WebFinder.pdf and an article on observing the ice giants is posted at skyandtelescope.org/observing/ice-giants-neptune-and-uranus/
Click on skyandtelescope.org/observing/interactive-sky-watching-tools/ 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 visible again until next year.
For more on the planets and how to locate them, see www.nakedeyeplanets.com/
The graphic at www.timeanddate.com/astronomy/planets/distance displays the apparent and comparative sizes of the planets, along with their magnitudes and distances, for a given date and time.
Comet C/2021A1 (Leonard), the brightest comet of the year, travels rapidly southeastward through Canes Venatici, Boötes, Serpens Caput, and Ophiuchus during the first part of December. It passes one degree to the east of the bright globular cluster M3 on the morning of December 3rd and some five degrees to the north of Arcturus on December 6th. The Earth will cross the orbital plane of Comet Leonard on December 8th. This comet may reach a peak brightness of fourth magnitude on December 12th when it passes within 0.23 astronomical units of the Earth and possibly first magnitude on December 14th due to forward scattering as a result of a phase angle of 160 degrees. However, there are signs that dust production has diminished and the comet may only reach second magnitude as a result. Comet Leonard enters the evening sky on December 12th and may be potentially visible to mid-northern observers around December 14 or December 15th. It passes five degrees below Venus on the evening of December 17th and within 2.6 million miles of that planet on December 18th. The speedy comet will attain an altitude of about five degrees above the southwestern horizon on December 22nd. An article on Comet Leonard appears on pages 48 and 49 of the December 2021 issue of Sky & Telescope. Other comets brighter than tenth magnitude include C/2019 L3 (ATLAS), 19P/Borrelly, and 67P/Churyumov-Gerasimenko. For additional information on comets visible this month, browse cometchasing.skyhound.com/ and www.aerith.net/comet/future-n.html and cobs.si/
A list of the closest approaches of comets to the Earth is posted at www.cometography.com/nearcomet.html
Asteroid 1 Ceres shines at seventh magnitude as it heads northwestward through Taurus this month. Asteroid 44 Nysa (magnitude +9.1) is at opposition in Taurus on December 10th. For information on this year’s bright asteroids and upcoming asteroid occultation events respectively, consult curtrenz.com/asteroids.html and asteroidoccultation.com/
A wealth of current information on solar system celestial bodies is posted at nineplanets.org/ and www.curtrenz.com/astronomy.html
Information on the celestial events transpiring each week can be found at astronomy.com/skythisweek and www.skyandtelescope.com/observing/sky-at-a-glance/
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 2nd, 5th, 8th, 11th, 13th, 16th, 19th, 22nd, 25th, 28th, and 31st. Consult www.skyandtelescope.com/observing/interactive-sky-watching-tools/ and page 50 of the December 2021 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 2:49 a.m. EST on December 4th, 11:38 p.m. EST on December 7th, 8:27 p.m. EST on December 10th, 1:22 a.m. EST on December 27th, and 10:11 p.m. EST December 30th. 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 stars.astro.illinois.edu/sow/Algol.html and www.solstation.com/stars2/algol3.htm
Free star charts for the month can be downloaded at www.skymaps.com/downloads.html and www.telescope.com/content.jsp?pageName=Monthly-Star-Chart and whatsouttonight.com/
Data on current supernovae can be found at www.rochesterastronomy.org/snimages/
Finder charts for the Messier objects and other deep-sky objects are posted at freestarcharts.com/messier and freestarcharts.com/ngc-ic and www.cambridge.org/turnleft/seasonal_skies_october-december
Telrad finder charts for the Messier Catalog and the SAC’s 110 Best of the NGC are posted at www.custerobservatory.org/docs/messier2.pdf and sao64.free.fr/observations/catalogues/cataloguesac.pdf respectively.
Information pertaining to observing some of the more prominent Messier galaxies can be found at www.cloudynights.com/topic/358295-how-to-locate-some-of-the-major-messier-galaxies-and-helpful-advice-for-novice-amateur-astronomers/
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 www.philharrington.net/tuba.htm
Stellarium and Cartes du Ciel are useful freeware planetarium programs that are available at stellarium.org/ and www.ap-i.net/skychart/en/start
Deep-sky object list generators can be found at www.virtualcolony.com/sac/ and tonightssky.com/MainPage.php and telescopius.com/
Freeware sky atlases of varying "depth" can be downloaded at www.deepskywatch.com/deep-sky-hunter-atlas.html and www.olle-eriksson.com/night-sky-maps/ and allans-stuff.com/takis-8-5-magnitude-star-atlas/
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.