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December 2016 Skies

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December Skies

by Dick Cookman


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

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

Comet Journal

Comet 45P/Honda-Mrkos-Pajdusakova has a short period, 5.25 year, orbit and may achieve 10th magnitude when briefly visible in Sagittarius during early December. It will be too close to the Sun to see in late December and will appear in the morning sky in early 2017 after passing through perihelion on Dec. 31st. It is expected to stay at about 7th magnitude as it circuits through northern predawn skies from January and February.

C/2016 U1 (NEOWISE) is another subvisual comet best seen in January when it passes through perihelion on the 14th. It moves from the end of the tail of Ursa Major to Ophiuchus in December and may increase from 12th to 8th magnitude.

2P Enke, V2 Johnson, and 41P/Tuttle-Giacobini-Kresak are potential naked eye candidates on the doorstep for 2017.

Mars Landers

From Sol 4521 (Oct. 11, 2016) through Sol 4534 (Oct. 26, 2016) Opportunity was at Spirit Mound on the rim of Endeavor Crater, the first science waypoint of the 10th extended mission.

The rover prepared for observation of the Schiaparelli EDM entry, descent and landing, and imaged the expected landing area on Sol 4528 (Oct. 19, 2016). No evidence of the lander was found even though Schiaparelli performed all entry functions, measurements, and communications without flaw. During descent a one second malfunction of the Inertial Measurement Unit (IMU) resulted in an altitude determination error and a premature parachute release. The resulting crash evidently destroyed the lander. Opportunity relinquished relay support to EDM until the 26th when science activities at Spirit Mound were resumed.

On Sol 4546 (Nov. 6, 2016), the rover drove about 112 feet (34 meters) to the south-southwest, heading for the next waypoint, the “gully”. After traveling east about 39 feet (12 meters) on Sol 4550 (Nov. 10, 2016) the mission was interrupted on Sol 4552 (Nov. 12, 2016) by excessive wheel current due to a sharp turn on a steep slope, so the rover continued for another 39 feet to gentler slopes. Steep slopes and scattered boulders necessitated imaging following the drive on Sol 4559 (Nov.19, 2016) to find a route forward and the Sol 4566 (Nov. 27, 2016) drive of 56 feet (17 meters) was followed by an additional 82 feet (25 meters) on Sol 4568 (Nov. 29, 2016). Solar array energy production is 465 watt-hours and total odometry is 27.05 miles (43.52 kilometers).

After drilling into and sampling the lacustrine (lakebed) sedimentary rock of the Murray Formation at Quela on the flank of Mt. Sharp on Sol 1465, Curiosity continued uphill, arriving at the next drilling target, Sebina, on Sol 1491, October 14, 2016. Further tests were performed on the Quela tailings and on the Sebina rock outcrop before proceeding with the drilling program on Sol 1495 after which the upward journey resumed on Sol 1500, October 24, 2016. After completing 1500 kilometers of total travel on Mars on Sol 1528, Curiosity reached the next drilling site in the Murray Formation called Precipice on November 21, 2016. The science laboratory also conducted numerous atmospheric observations along with detailed outcrop and panoramic imaging of the rocks and landforms along the route. Drilling of Precipice in currently on a delay due to drill malfunction which is currently being evaluated.

Meteor Showers

The Geminid Meteor Shower peaks on the 13th, the night of the Full Moon. The source of the shower was unknown until 1983 when Fred Whipple noticed that an object later named 3200 Phaeton had an almost identical 1.5 year orbit. It will again pass through our orbit in 2017 and may be an asteroid or an ancient bare comet, denuded of its volatiles.

Since the meteors emanate from Gemini and the Moon is in nearby Taurus, meteors hidden in its glare will not appear unless they streak well away from the Moon. In years when the Moon or clouds don't interfere, the Geminids have supplanted the August Perseids as the most dependable meteor shower, typically exhibiting 50 to 130 meteors per hour in skies free of light pollution.

Observers may have a better view of the Ursid Meteor Shower on the 22nd. The shower normally produces a few fireballs and 10 to 50 meteors per hour in dark skies, meteors which will not have to contend with a Full Moon. The comet which produced the debris causing the Ursids is Comet 8P Tuttle which has a 13.5 year orbit and last visited in January, 2008.

December Solstice

On the Winter Solstice at 5:44AM EST on the 21st, the axis of the Earth achieves its maximum tilt away from the Sun which will rise at its southernmost spot on the eastern horizon. For observers in the northern United States at 45° N, the bearing of the rising Sun will be 124° or 34° south of east. For those in the southern United States at 30° N, the bearing will be 117° or 27° south of east. The Sun's altitude above south at solar noon will be 21.5° and 36.5° respectively, the lowest of the year. Sunset bearings will be 236° (34° south of west) and 243° (27° south of west) for northern and southern observers.

At latitude 40°N, the latest sunrise of the year is on January 5th. The earliest sunset occurs on December 7th. The dates of each get closer to the solstice as latitude increases. Even though the solstice is the shortest day of the year, neither of the above coincides with the solstice because we measure the times of sunrises and sunsets by mean solar time (clock time), not local solar time (sundial time).

The tilt of Earth's axis does not change through the year but its angle from the Sun changes as Earth revolves around its orbit. The northern hemisphere is cooled when it tilts away from the Sun in the winter and is warmed when tilting toward the Sun in the Summer. In addition to this annual change in tilt relative to the Sun, the axis tilt of 23.5° cycles from 21° to 24.5° with a very long period of 40,000 years. At low tilt, summers are cooler and winters warmer. At higher tilt, the reverse occurs.

Planet Plotting

Mercury (-0.5 to -0.3) in Sagittarius reaches Maximum Elongation of the 10th when it is 21° from the Sun and 7° above the southwestern horizon 30 minutes after sunset. Venus (-4.1 to -4.4) is very bright in the southwestern sky and provides its best apparition of the year as it rises from 15° to 25° above the horizon an hour after sunset during December. It moves from Sagittarius to Capricornus during the month. Mars (+0.5 to +0.9) in Capricornus and Aquarius is higher than Venus in the southwestern sky after sunset and Venus will close the distance from the red planet as Mars moves toward Neptune (+7.9) in Aquarius during December. By the New Year, Mars and Neptune will appear closer to one another than at any other time during the last 700+ years. Uranus (+5.8) in Pisces is in the southern sky after sunset and sets after midnight.

Jupiter (-1.8 to -1.9) rises in Virgo as Uranus sets in the west. It ascends to about 30° above the southeastern horizon by an hour before morning twilight and dominates the predawn sky. Saturn (+0.5) in Ophiuchus is in conjunction with the Sun on the 10th and is lost in its glare until late in the month when it makes its appearance in the morning sky. By the 31st, it rises in the southeast about 45 minutes before the Sun.

PlanetConstellationMagnitudePlanet Passages
SunOphiuchus, Sagittarius-26.8New Moon, 11/29, 7:18AM EST
MercurySagittarius-0.5 to -0.3Max. E. Elong. 12/10, Midnight EST
Inferior Solar Conjunction 12/28, 2PM EST
VenusSagittarius, Capricornus-4.1 to 4.4 
MarsCapricornus, Aquarius+0.5 to +0.9Neptune, 0.1°N. 12/31, 9PM EST
JupiterVirgo-1.8 to -1.9 
SaturnOphiuchus+0.5Solar Conjunction, 12/10, 7AM EST

December Moon

The New Moon of December is on the 29th at 1:53AM EST. The New Moon is the beginning of Lunation 1163 which ends 29.72 days later with the New Moon of January 27th at 7:07PM EST.

The Full Moon in December in Taurus occurs at 7:06PM EST on the 13th. It is just below the horns of the Bull and was above the Bull in November. Ignoring the issue of gender, the cow has jumped over the Moon, just like Mother Goose told us.

The December Moon is called the “Moon before Yule”. Colonial Americans used the term “Christmas Moon”. The Celts called it the “Cold Moon”, and the Chinese agree when they refer to it as the “Bitter Moon”. Medieval English thought of it as the “Oak Moon”, and the Anishinaabe (Odawa and Ojibwe) people of northern Michigan recognize it as “Manidoo-gizisoons” (Little Spirit Moon).

Lunar perigee distance (closest to Earth) is 222,737 miles or 56.21 Earth radii on the 12th at 6:29PM EST. Full Moon occurs 24+ hours later, producing a large “Supermoon” which is slightly smaller than that of November. The Moon is at the apogee position in orbit (maximum orbital distance) at 252,196 miles (63.63 Earth radii) from Earth on the 25th at 12:55AM EST.

Cecil Adams’ reasons why we need the Moon:
“Reason #2: It keeps us toasty. The impact of a planetary object about the size of Mars with the primordial Earth also contributed to the heating of earth’s iron core, which provides us with our relatively strong magnetic field. This in turn protects us from (cancer causing) radiation..and solar winds. And the pull of the moon’s gravity acts on every molecule on earth, powering the tides..and creating additional heat, which helps keep the core from cooling too quickly”.

PlanetConstellationMagnitudeMoon PassageMoon Phase/Age
SunSagittarius-26.87:18AM EST, 12/29New ~ 0 days
MercurySagittarius-0.31.8°N, Midnight EST, 12/29Waning Crescent ~ 29.7 days
VenusSagittarius-4.16.0°N, 8AM EST, 12/3Waxing Crescent ~ 4.03 days
MarsCapricornus+0.53.0°N, 6AM EST, 12/5Waxing Crescent ~ 5.95 days
JupiterVirgo-1.92.0°N, Noon EST, 12/22Waning Crescent ~ 23.20 days
SaturnOphiuchus+0.54.0°N, 4PM EDT, 12/27Waning Crescent ~ 28.36 days
UranusPisces+5.83.0°S, 3PM EST, 12/9Waxing Gibbous ~ 10.32 days
NeptuneAquarius+7.90.7°N, 5PM EST, 12/6Waxing Crescent ~ 7.40 days

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