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December 2010 Celestial Calendar & Observing Notes c/o Dave Mitsky

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December 2010 Celestial Calendar & Observing Notes courtesy of Dave Mitsky (calendar data also reproduced in our forum calendar).

All times, unless otherwise noted, are UT.

2/1 Mercury is at greatest eastern elongation (21 degrees) at 15:00; Saturn is 8 degrees north of the Moon at 18:00; Mercury is 1.3 degrees south of the bright emission nebula M8 (the Lagoon Nebula) in Sagittarius at 23:00

12/2 Venus is 6 degrees north of the Moon at 21:00

12/4 The earliest end of evening twilight at 40 degrees north latitude occurs today; Venus (magnitude -4.9) is at greatest brilliancy at 10:00

12/5 New Moon (lunation 1088) occurs at 17:36

12/6 Uranus is stationary at 10:00; Mars is 0.5 degree south of the Moon at 22:00

12/7 The earliest sunset of 2010 at 40 degrees north latitude occurs today; Mercury is 1.8 degrees south of the Moon at 9:00

12/9 Asteroid 16 Psyche (magnitude 9.4) is at opposition at 2:00

12/10 Mercury is stationary at 10:00

12/11 Neptune is 5 degrees south of the Moon at 15:00

12/13 Mercury is at the ascending node today; the Moon is at apogee, subtending 29'16" from a distance of 404,406 kilometers (251,286 miles), at 8:34; the Lunar X (the 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 occur at 8:41; First Quarter Moon occurs at 13:59

12/14 Jupiter is 7 degrees south of the Moon at 2:00; Uranus is 7 degrees south of the Moon at 6:00; the peak of the Geminid meteor shower (100 to 120 per hour) occurs at 11:00

12/18 Mercury is at perihelion today

12/19 The Moon is 1.2 degrees south of the bright open cluster M45 (the Pleiades) in Taurus at 3:00

12/20 Mercury is in inferior conjunction at 1:00

12/21 A total lunar eclipse begins at 7:40:47 and ends at 8:53:08, reaching maximum eclipse at 8:16:57; Full Moon (known as the Before Yule, Cold, Long Nights, and Oak Moon) occurs at 8:13; the Moon is 0.9 degree south of the bright open cluster M35 in Gemini at 13:00; the northern hemisphere winter solstice occurs at 23:38

12/22 Asteroid 2 Pallas is in conjunction with the Sun at 17:00; the peak of the Ursid meteor shower (10 per hour) occurs at 19:00

12/25 The Moon is at perigee, subtending 32'41" from a distance of 368,465 kilometers (228,954 miles), at 12:16; a double Galilean satellite shadow transit (Io’s shadow follows Europa’s) begins at 22:46

12/27 Pluto is in conjunction with the Sun today; Venus is at perihelion today; a double Galilean satellite shadow transit (Europa’s shadow follows Ganymede’s) begins at 1:07

12/28 Mercury is at its greatest heliocentric latitude north today; Last Quarter Moon occurs at 4:18

12/29 Saturn is 8 degrees north of the Moon at 3:00; a double Galilean satellite shadow transit (Europa’s shadow follows Io’s) begins at 11:56; the Curtiss Cross, an X-shaped illumination effect located between the craters Parry and Gambart, is predicted to occur at 12:30

12/30 Mercury is stationary at 8:00

12/31 Venus is 7 degrees north of the Moon at 16:00

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

The peak of the Geminid meteor shower takes place after midnight on the morning of December 14. This shower, which is associated with the asteroid (or possible cometary nucleus) 3200 Phaethon, has become the most reliable one of the year. Geminids appear to originate from a radiant that’s a bit northwest of Alpha Geminorum (Castor). The Ursids, a normally minor meteor shower, peak on December 22. The radiant is located close to Beta Ursa Minoris (Kochab), some 15 degrees from the north celestial pole. For more on these meteor showers, click on IMO Meteor Shower Calendar 2009 | International Meteor Organization

The Moon is 24.5 days old and is located in Virgo on December 1 at 0:00 UT. It attains its greatest northern declination (+24.2 degrees) for the month on December 20 and its greatest southern declination (-24.2 degrees) for the month on December 6. Longitudinal libration is at a maximum of +5.4 degrees on December 6 and a minimum of -5.2 degrees on December 19. Latitudinal libration is at a maximum of +6.8 degrees on December 27 and a minimum of -6.9 degrees on December 14. A 72-minute-long total lunar eclipse that’s visible from North America and western South America takes place on December 21. (Partial eclipse begins at 1:33 a.m. EST and ends at 5:01 a.m. EST.) The Moon will be located in Taurus at the time. There’s additional information on the eclipse posted at NASA - Eclipses During 2010 and at Total Lunar Eclipse on December 21, 2010 and in an article on pages 61-63 of the December issue of Sky & Telescope. Visit Extreme Lunar Crescent Data [L1088-1102] | Saber Does The Stars for tips on spotting extreme crescent Moons. Browse Web Page Redirection for IOTA for information on upcoming lunar occultations. Times and dates for the lunar light rays predicted to occur this month are available at Lunar Sunrise/Sunset Crater Rays

The Sun is located in Ophiuchus on December 1. When the winter solstice for the northern hemisphere occurs on December 21, there will be 9 hours and 20 minutes of daylight at latitude 40 degrees north.

Brightness, apparent size, illumination, distance from the Earth in astronomical units, and location data for the planets and Pluto on December 1: Mercury (-0.4 magnitude, 6.5", 65% illuminated, 1.03 a.u., Sagittarius), Venus (-4.9 magnitude, 42.4", 24% illuminated, 0.39 a.u., Virgo), Mars (1.3 magnitude, 4.0", 99% illuminated, 2.37 a.u., Ophiuchus), Jupiter (-2.6 magnitude, 42.8", 99% illuminated, 4.60 a.u., Aquarius), Saturn (0.9 magnitude, 16.4", 100% illuminated, 10.12 a.u., Virgo), Uranus (5.8 magnitude, 3.5", 100% illuminated, 19.76 a.u., Pisces), Neptune (7.9 magnitude, 2.2", 100% illuminated, 30.21 a.u., Capricornus), and Pluto (14.1 magnitude, 0.1", 100% illuminated, 32.83 a.u., Sagittarius).

During the evening, Mercury and Mars can be found in the southwest (in the early part of the month), Jupiter and Uranus in the south, and Neptune in the southwest. In the morning, Mercury (in the latter part of December), Venus, and Saturn are located in the southeast.

At mid-month, Venus rises at 4:00 a.m. EST, Jupiter transits at 6:00 p.m. EST and sets at midnight, and Saturn rises at 2:00 a.m. EST for observers at latitude 40 degrees north.

Mercury reaches greatest eastern elongation on December 1, during the course of an evening apparition that is unfavorable for northern hemisphere observers. On December 7, the speediest of planets is 8 arc minutes in angular diameter, is 40% illuminated, and is situated 7 degrees to the lower right of the Moon. During the first nine days of the month, Mercury decreases in illumination from 65 to 33% and in magnitude from -0.4 to 0.2. Mercury passes one degree north of Mars some 30 minutes after sunset on December 13. Seven days later Mercury is in inferior conjunction. It reappears in the evening sky at the end of December. On December 31, Mercury is ten degrees above the southeastern horizon a half hour before the Sun rises.

Venus rises three hours before the Sun on December 4, when it reaches greatest brilliancy. At magnitude -4.9, it is 25 times brighter than the brightest nighttime star Sirius, the Dog Star. During the course of the month, Venus increases in illuminated extent from 24 to 45%, while its apparent size decreases from 42 to 27 arc minutes. At mid-month, the brightest planet is 30 degrees in altitude when the Sun rises. The Moon is near Venus on December 2 and December 31.

Mars is not visible to the naked eye this month. An occultation of Mars by a very thin crescent Moon takes place during evening twilight on December 6. For more on this difficult to observe event, see Occultation of a Planet

Jupiter’s “missing” South Equatorial Belt (SEB) may be beginning to reappear. On December 13, the First Quarter Moon lies in the Circlet of Pisces, seven degrees north of Jupiter. By December 15, Jupiter has dropped to magnitude -2.4 and subtends only 40 arc seconds. The King of the Planets is at eastern quadrature on December 16. Jupiter will pass very near the fifth-magnitude star 20 Piscium on December 29. Browse SkyandTelescope.com - Planets - Transit Times of Jupiter's Great Red Spot in order to determine transit times of Jupiter’s central meridian by the Great Red Spot. Data on the Galilean satellites is available at SkyandTelescope.com - Interactive Observing Tools - Jupiter's Moons Javascript Utility

The Ringed Planet rises about two hours after Jupiter sets. Its rings are inclined by nine degrees in early December. The ring tilt increases to ten degrees by the end of the year, making the Cassini Division an easy telescopic target. The Moon is 8 degrees south of Saturn on the night of December 28. For further information on the five brightest satellites of Saturn, browse SkyandTelescope.com - Interactive Observing Tools - Saturn's Moons Javascript Utility

As the month begins, Uranus is approximately three degrees east of Jupiter. By month’s end, the two gas giants are within 40 arc minutes of each other.

Neptune can be found near the fifth-magnitude star Mu Capricorni.

Finder charts for Uranus and Neptune are posted at http://media.skyandtelescope.com/documents/Uranus_Neptune_2010.pdf

The dwarf planet Pluto is in conjunction with the Sun on December 27 and is not visible this month.

This month Comet 103P/Hartley loops westward through Puppis and into Canis Major. It’s located just south of the open clusters M46 and M47 on December 1. Visit Comet Chasing for additional information on comets that are visible this month.

During December, asteroid 7 Iris (magnitude 8.6) heads southwestward through Cancer. It’s positioned a couple of degrees to the north of the sixth-magnitude open cluster M67, during the first part of the month, then passes to the northwest of the cluster.

A free star map for December can be downloaded at Skymaps.com - Publication Quality Sky Maps & Star Charts

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