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December Skies


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December Skies

by Dick Cookman

12/4/2013

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

Focus Constellations: Ursa Major, Ursa Minor, Draco, Cepheus, Cassiopeia, Camelopardalis, Lynx, Gemini, Auriga, Perseus, Pegasus, Andromeda

Comet Journal

Comet ISON exceeded a magnitude of 3.6 prior to passage through perihelion and was reported to achieve 1st magnitude by some observers when it disappeared behind the Sun on 11/28/13. Although it survived dancing with the Sun, initial reports indicated that quite a bit of the comet nucleus disintegrated leaving a remnant of as yet undetermined size. There was enough left to produce a small tail which began to increase in size and the comet started to get brighter. The increase was short lived as views from space revealed the comet rapidly fading into a cloud of dust. Observations attempted from a plane flying at 36,000 feet above the Arctic Circle were also unsuccessful, indicating that the comet may have disintegrated and will not be visible again.

Comet behavior is always hard to predict, especially when passing close to the Sun and Comet ISON passed closer than any comet in modern times. Although observers prematurely declared ISON dead immediately after it passed through perihelion, it extricated itself from the grave and may do so again. A few more days will tell the story. If it disinters itself again, look for it to move northward through December skies into northern Hercules by Christmas when it could be visible in both morning and evening skies.

Comet C/2013 R1 (Lovejoy) is in northern Bootes at almost 4th magnitude and will move into and through central Hercules in January. It will drop slightly to 5th magnitude in February and fade to 8th magnitude in March. It is the surprise comet of the season, discovered on Sept. 7th by Australian Terry Lovejoy, and reaching visibility to the naked eye in early November when it moved into northern skies. The comet was brightest when it passed closest to Earth on the 19th and will remain bright throughout the Christmas season. With the exception of Nov. 27th and 28th when ISON was at its brightest, Comet Lovejoy was consistently brighter and will remain in the eastern sky before dawn as it passes through perihelion on Dec. 22nd when it will be about 75 million miles above the Sun.

Mars Landers

Opportunity is ascending the north facing southern slope of a westward trending valley cut into Solander Point. After making numerous observations of Kangaroo Paw, the first rock outcrop encountered on its ascent the rover moved on to the next outcrop called Waratah on Sol 3467 (Oct. 24, 2013). By November 5th, Opportunity had traveled over 250 feet southward in its ascent and circuited a small dune field after sampling some of the dust comprising the dunes.

The rover is maintaining a northward tilt as it climbs so as to maximize solar gain. Mission scientists hope to keep it operating throughout the upcoming winter by choosing a path which keeps the solar panels in optimal orientation. Movement between the 5th and 21st was limited by the cold weather causing increased discharge of the batteries despite solar array energy production providing 302 watt-hours on the 21st.

As Curiosity approached an intriguing rock outcrop called Cooperstown representing the layered material visible in the orbital images, the rover experienced a warm reset on November 8th. This alerted mission scientists of an electrical fault in one of the systems. The warm reset was the first experienced by the rover during its time on Mars. After evaluating available data for potential causes of the reset, the rover was taken out of the safe mode on the 12th only to experience an anomalous voltage drop on the 17th which appears to be unrelated to the reset on the 8th.

The voltage drop of 11 to 4 volts was within operation range so the rover did not shift to safe mode. As of November 20th, team members were still evaluating potential causes. Operations planned for Curiosity for the next few days are designed to check some of the possible root causes for the voltage change. Analysis so far has determined that the change appeared intermittently three times during the hours before it became persistent.

Participating scientist Kevin Lewis of Princeton University stated of the rock outcrop: "We want to see how the local layered outcrop at Cooperstown may help us relate the geology of Yellowknife Bay to the geology of Mount Sharp."

Meteor Showers

The Geminid Meteor Shower (December 12/13) is a quite active shower which has to contend with the bright waxing gibbous Moon in the evening. After moonset at 4AM, there will be an hour of dark skies before the glow of dawn lights up the eastern horizon. By then the radiant of the shower in Gemini will be well into the western sky providing a good view of the shower which occasionally has produced over 100 meteors per hour. According to NASA, the Geminids are not ordinary meteors. While most meteor showers come from comets, Geminids come from an asteroid. The PHA (potentially hazardous asteroid) named 3200 Phaethon which produced the debris is a near Earth asteroid which circuits passed Earth every 1.4 years and orbits closer to the Sun than any other known asteroid (hence the name).

The Ursids on the 22nd result from debris associated with previous passages of Comet 89/Tuttle which last passed though in 2008. The waning gibbous Moon will provide major competition for the shower.

Winter Solstice

The solstice in December is on the 21st at 12:11PM EST. The Earth will be positioned in its orbit so that its axis will be tipped 23.5° away from the Sun and the rays of the Sun will be perpendicular to the surface of the planet on the Tropic of Cancer at 23.5° South latitude. At 45° North latitude the Sun at Noon will be 68.5° south of the zenith and 21.5° above the south point on the horizon, its lowest altitude of the year. The coldest part of the year in the northern hemisphere typically occurs during the months immediately following the December Solstice due to the required time for dissipation of heat gained in summer and stored in the land and water bodies. Snow and ice coverage is also concentrated in the months following the solstice due to the cooler temperatures which are enhanced by greater reflection of solar energy.

Governmental and business energy use statistics focus on the fossil and nuclear fuels, ignoring solar energy. How many gallons of oil or tons of coal would it take to totally replace the Sun?

Planet Plotting

Venus is in Sagittarius is the evening planet in the southwest after sunset, gleaming more brightly than it has throughout the year. It is also highest in the sky in early December and does not set until about 2 hours after the Sun. Neptune (+7.9 in Aquarius) is between Venus and Uranus (+5.8 in Pisces) which is half way between the horizon and the zenith in the southern sky. Both planets are visible in 7x50 binoculars. Mercury has its Superior Conjunction with the Sun on the 29th when it lies precisely on the other side of the Sun. As a result, viewing of the fleet planet is limited to the early part of the month in the morning sky when it is in Libra and Scorpius. On the morning of the 1st, it joins a thin crescent Moon and distant Saturn in Libra in the east-southeast just before sunrise. Jupiter is visible all night and Mars is a morning planet. Jupiter in Gemini and Mars in Virgo rise in the northeast about 7PM EDT and 1AM EDT respectively on the 1st.

Mars and Jupiter will get brighter in December and early 2014 as Jupiter approaches opposition in early January.

PlanetConstellationMagnitudePlanet Passages
SunScorpius, Ophiuchus, Sagittarius-26.8New Moon, 12/2, 7:22PM EST
MercuryLibra, Scorpius, Ophiuchus, Sagittarius Superior Conjunction 12/29, 1AM EST
VenusSagittarius-4.8 to -4.5 
MarsVirgo+1.2 to +0.8 
JupiterGemini-2.6 to -2.7 
SaturnLibra+0.6 
UranusPisces+5.8 
NeptuneAquarius+7.9 

December Moon

The New Moon in December is at 7:22PM EST on the 2nd. It marks the start of Lunation 1125 which is 29.95 days long and ends with the New Moon of January on the 1st. The Full Moon is in Taurus on December 17th at 4:28AM EST. It is the "Moon before Yule" or the "Long Night Moon." Colonial Americans called it the "Christmas Moon" and Celts referred to it as the "Cold Moon". Chinese call it the "Bitter Moon" and Medieval English named it the "Oak Moon". The Anishnaabe (Chippewa and Ojibwe) of northern Michigan call it "Manidoo-gizisoons" (Small Spirits Moon).

The Moon is closest to Earth at perigee on the 4th at 4:22AM EST. It will be 223,735 miles away or 56.45 Earth Radii. The proximity of perigee and New Moon will produce higher than normal ocean tides.

On the Great Lakes the tides are much smaller with maximums occurring on Lakes Superior and Erie which are limited to about 2 inches and on Green Bay which can reach 4 inches. There simply isn't enough water in the Great Lakes to develop higher tides although the tides that they experience are superimposed on land (or Earth) tides which average about 12 inches due to the flexibility of the Earth's crust.

On the 19th, the Moon is at apogee at 4:49AM EST, it will be 252,444 miles away or at a distance of 63.70 Earth radii.

PlanetConstellationMagnitudeMoon PassageMoon Phase/Age
SunLibra-26.87:22PM EST, 12/2New ~ 0 days
MercuryLibra+1.00.53°NE, 6PM EDT, 12/1Waning Crescent ~ 28.42 days
VenusSagittarius-4.68.0°N, 7PM EST, 12/5Waxing Crescent ~ 3.49 days
MarsVirgo+1.15.0°S, 10PM EST, 12/25Waning Crescent ~ 23.61 days
JupiterGemini-2.65.0°S, 2AM EST, 12/19Waning Gibbous ~ 16.78 days
SaturnLibra+0.61.3°S, 5AM EST, 12/1Waning Crescent ~ 28.42 days
SaturnLibra+0.60.9°S, 8PM EST, 12/28Waning Crescent ~ 26.53 days
UranusPisces+5.83.0°N, 2AM EST, 12/11Waxing Gibbous ~ 8.78 days
NeptuneAquarius..+7.96.0°N, Noon EST, 12/8Waxing Gibbous ~ 6.19 days




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