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December Skies

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December Skies

by Dick Cookman


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

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

Comet Journal

Comet C/2011 L4 (PanSTARRS) has reached a strong 10th magnitude and is in Lupus. It will move into southern Scorpius in December and will probably be easily visible to the naked eye when it appears in predawn skies in Pisces in March. Comet PanSTARRS may be the first of the Great Comets of 2013. It could be as bright as 1st magnitude when nearest Earth on March 5th and near perihelion on March 10th!

If Comet PanSTARRS becomes a Great Comet, Comet C/2012 S1 (ISON) may be a Super Comet! It will circle through northern Gemini until early August, 2013 when it enters Cancer and starts its eastward journey along the ecliptic. The comet is beyond the orbit of Jupiter and moving toward the Sun. By late summer it may be visible in a 4 inch diameter telescope and after passing above the orbit of Mars in late September may be seen with binoculars. Naked eye visibility is predicted to arrive in November when it flies over Earth's January orbital location. Although predictions of comet brightness near perihelion are fraught with peril, by late November, 2013 the comet may even exceed Venus in brightness in predawn skies near Libra when it is near perihelion less than 1.3 million miles from the Sun. After circling the Sun, the comet will start its outward journey and barely avoid homebound Santa Claus as it passes less than 0.5 a.u. above Earth's north pole when closest to Earth on Dec. 26th.

Comet 2011 F1 (Linear) will reach perihelion on January 8th, 2013. It is at 9th magnitude and rises in the east in southern Ophiuchus just before dawn. It will descend through the inner asteroid belt on the other side of the Sun in mid-December and will not be visible for northern observers as it drops farther into southern skies.

Comet C/2012 K5 ( LINEAR ) is approaching 10th magnitude as it nears Alkaid in Ursa Major on Dec. 7th. From the 7th to the 18th it will trace a path from the end of the handle of the Big Dipper to the cup. The comet came out of deep space to be discovered in May, 2012. Passing far above Earth's orbit in July and August, it reached perihelion above the Sun in late November. The comet drops through the solar system plane only 0.29 A.U. beyond Earth on New Years Day when it could reach 8th magnitude in Auriga. It will then diminish in brightness and disappear from northern skies in the Spring.

Martian Landers

Soil samples collected by Curiosity contain substances characteristic of basaltic volcanics. Sample testing with the rovers instruments produced gases comprised of water, sulfur and perchlorate (a combination of chlorine and oxygen).

A dusty sand sample collected on Sol 74 (Oct. 20) was shaken in the rover's sample-handling mechanism on Sol 75 (Oct. 21, 2012) as a 3rd scrubbing of the mechanism to remove material of Earth origin. A sieved portion of sample was then delivered to the observation tray on the 22nd This was the second sample for CheMin analysis. X-ray diffraction studies revealed the presence of the mineral olivine (iron, magnesium silicate) and other substances similar to the type of chemistry found in weathered products of basaltic volcanics typical of the rock associations found in areas like the Hawaiian Islands.

Another sample was collected and placed on the inlet port of the SAM instrument (Sample Analysis at Mars) on Nov. 9th. SAM investigates samples with mass spectrometry, gas chromatography and laser spectrometry. A portion of the sample was also supplied to the CheMin instrument. Results of these analyses revealed the gases described above.

Curiosity also conducted dozens of tests on Martian air and airborne dust samples. These reveal unexpected complex wind and weather patterns. Evidently summer heating of polar caps injects large amounts of carbon dioxide into the atmosphere altering atmospheric heat retention and generating planetary wind pattern change and global dust storms. Examination of the details of these changes may help scientists gain deeper understanding of climate change on Earth.

From October 23rd (Sol 3110) through November 28th (Sol 3145), Opportunity traveled about 240 meters while completing its circumnavigation of Matijevic Hill on the western margin of Endeavor Crater at the south end of Cape York, the elongated ridge stretching one half mile north-northeastward from Botany Bay. The solar array energy production decreased during the interval by almost 8% as a major dust storm passed over 800 miles south of the rover. The storm appears to be dissipating negating fears that a planet-wide dust storm could interrupt operations. Dust storms are monitored from orbit and by Opportunity and Curiosity due to their potential effects.

Meteor Showers

The Geminid meteor shower on the night of December 12-14 coincides with New Moon providing sufficiently dark skies to observe peak rates of up to 2 meteors per minute in areas without light pollution. The shower is one of the best of the year and maximum rates will occur during the hours before dawn when we are on Earth's leading edge as it dives into the debris swarm made up of residue from Phaeton, the Earth orbit crossing asteroid which orbits every 1.4 years.

The Ursids on the 22nd are a more subtle shower which can produce up to one meteor per minute but more typically are limited to 10 per hour. The waxing gibbous Moon will produce enough glare to dim the faint, medium speed meteors until after moonset at 2AM. Best viewing will be in the predawn hours. Comet 8P/Tuttle which last circuited through the inner solar system in 2008 produced the river of debris which crosses Earth's orbit and generates the shower.

Planet Plotting

The evening planets in December include Mars, Neptune, Uranus, and Jupiter. Mars (+1.2) is in Sagittarius during the first half of the month and can be seen in the western twilight skies well after sunset. It falls slightly deeper into the afterglow of the Sun as it moves into Capricornus in the latter part of the month. Mars will diminish in brightness by almost one third in the next 5 months until it reaches conjunction with the Sun in April, 2013. Neptune (+7.9) in Aquarius sets by 10PM and can be seen in binoculars held with a steady hand or on a tripod well after sunset. Uranus (+5.8) in Pisces is bright enough to see with the naked eye in moonless skies without light pollution. It sets around midnight and like Neptune is best viewed well after sunset. Jupiter (-2.8 in Taurus) is at opposition on the 2nd when it rises at sunset and sets as the Sun rises. It is at its brightest of the year and is high in the south at midnight. On the 7th the planet makes a relatively close pass (5°) to Aldebaran, the first magnitude star at the base of the horns of Taurus.

Saturn (+0.7 in Virgo) rises about 4AM in in early December and dims to magnitude +0.6 in late December as it moves into Libra. Mercury & Venus (-0.3 & -3.9 respectively in Libra) are the bright morning planets rising slightly before the Sun. They join Saturn on Dec. 1st in a group spanning less than 15° then separate from it as December progresses. Both move into Scorpius and then Ophiuchus in December. Mercury brightens to -0.6 magnitude as it moves more rapidly and is in Sagittarius by month's end.

Planet Constellation Magnitude Planet Passages
Sun Ophiuchus, Sagittarius -26.8  
Mercury Libra,Scorpius, Ophiuchus, Sagittarius -0.3 to -0.6 Maximum western Elongation 12/4, 6PM EST
Venus Libra,Scorpius,Ophiuchus -3.9  
Mars Sagittarius, Capricornus +1.2  
Jupiter Taurus -2.8 to -2.7  
Saturn Virgo, Libra +0.7 to +0.6  
Uranus Pisces +5.8  
Neptune Aquarius +7.9  

Winter Solstice and December Moon

The Winter Solstice occurs on the 21st at 6:12 AM EST when the Sun reaches its greatest distance below the celestial equator and its lowest altitude above the southern horizon. After the longest night, daylight hours will start to increase and the chickens will start to lay again.

Lunation 1112 began with the New Moon on Nov. 13th and ends with New Moon at 3:42 AM EST on Dec. 13th. It is 29.44 days long. is referred to as the "Moon before Yule" or the "Long Night Moon." Colonial Americans called it the "Christmas Moon" and to the Celts it was the "Cold Moon." Chinese call it the "Bitter" Moon. Medieval English named it the "Oak Moon" and northern Michigan Anishnaabe (Chippewa and Ojibwe) call it "Manidoo-gizisoons" (Small Spirits Moon).

The Moon is at perigee on the 12th at 6:14PM EST when it will be at 221,876 miles or 55.99 Earth radii, the second nearest in 2012. This is slightly more than 9 hours before the high "Spring Tide" associated with New Moon.

At apogee when the Moon is farthest from Earth on the 25th at 4:19PM EST, it will be at 63.67 Earth Radii or 252,337 miles. The Full Moon occurs 2.5 days later making its Spring Tide smaller than normal.

Planet Constellation Magnitude Moon Passage Moon Phase/Age
Sun Scorpius -26.8 3:42AM EST, 12/13 New ~ 0 days
Mercury Libra -0.5 1.1° S, 8PM EST, 12/11 Waning Crescent ~ 28.12 days
Venus Libra -3.9 1.6° S, 9AM EST, 12/11 Waning Crescent ~ 27.66 days
Mars Sagittarius +1.2 6.0° N, 5AM EST, 12/15 Waxing Crescent ~ 2.05 days
Jupiter Taurus -2.7 0.4° S, 7PM EST, 12/25 Waxing Gibbous ~ 12.64 days
Saturn Virgo +0.6 4.0° S, 7AM EST, 12/12 Waning Crescent ~ 28.58 days
Uranus Pisces +5.8 5.0° N, 3PM EST, 12/20 Waxing Gibbous ~ 7.47 days
Neptune Aquarius +7.9 6.0° N, 1AM EST, 12/18 Waxing Crescent ~ 4.33 days


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