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December 2017 Skies
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by Dick Cookman
Highlights: Comet Journal, Martian Landers, Meteor Showers, Winter Solstice, Planet Plotting, December Moon
Focus Constellations: Gemini, Auriga, Taurus, Perseus, Cassiopeia, Andromeda, Pegasus, Cepheus, Draco, Ursa Minor, Ursa Major, Camelopardalis, Lynx
No comet is expected to exceed 9th magnitude in December. Comet C/2017 O1 (ASASSN) circles through Cepheus in December at 9th magnitude. It is now retreating from the Sun and will get dimmer in 2018.
Opportunity is at "Perseverance Valley” on the western rim of "Endeavor Crater", the 14 mile wide crater located on "Meridiani Planum". The crater was formed during the ”Noachian“ age on Mars, over 3.7 billion years ago. The rover has been limited in its activities in recent weeks by wintry conditions which influenced availability of solar energy, limiting energy available for exploration.
Opportunity is conducting extensive panoramic imaging as it descends “Perseverance Valley” on the west rim of the crater. The valley may be a major drainage sluiceway carved by flowing water or mudflows. The rover has also conducted Alpha Particle X-ray spectrographic studies of rock samples so as to determine the nature of the material on the floor of the valley. As of Sol 4923 (Nov. 28, 2017), the rover reached total travel on Mars of 28.00 miles (45.068 kilometers). Solar array energy production was 390 watt-hours per sol.
Curiosity is in “Gale Crater” which is even older than "Endeavor Crater”. The 96 mile wide crater was filled with water laid sediments sometime after the impact which formed it. These sediments were buried, lithified into sedimentary rock layers, then almost completely eroded away except for “Mt. Sharp”, the 18,000 foot high remnant in the center of the crater. The rover is climbing the mountain and reached a summit on Vera Rubin Ridge on September 13th. Curiosity then started traversing southward over bedrock exposures and fractured bedrock material with overlying scattered surficial pebble(s) or soil and a general lack of sand. This is unlike the landscape in the Murray formation at the base of the ridge, which was dominated by a combination of bedrock exposures and windblown sands. For most of October, mission scientists devoted a major effort to deliver a sand sample collected over 18 months ago to the Sample Analysis at Mars (SAM) Instrument Suite. The instruments and mechanisms necessary for the task have been inoperable since the robotic arm’s drill feed mechanism became stuck on December, 2016. The sample was successfully delivered and the drill was tested on the ground on Sol 1863 (November, 1, 2017).
After an immobile two weeks in late October, travel resumed and Curiosity examined an outcrop of sedimentary rock with prominent sedimentary structures revealing how the sediment was initially deposited. The rover continued to climb southward over the Vera Rubin Ridge during November, then altered course to the east in early December. During the interval, daily observations of the rocks, sediments, terrain, and atmosphere were conducted with the Mast Camera (Mastcam) and the Chemistry and Camera Instrument (Chemcam) to provide scientists with the data necessary for understanding of the ridge and environment.
December Meteor Showers in December for the northern hemisphere include the Chi Orionids, the Geminids, the Coma Berenicids, and the Ursids. All are minor showers except for the Gemini's and, occasionally, the Ursids. The former peak on the 13th/14th and the latter on the 23rd/24th. The Gemini's often produce over 100 meteors per hour and the Ursids normally produce 5 to 10 meteors per hour and have stormed at 50 per hour. Dark skies associated with the accompanying crescent moons will favor each shower. The Geminid maximum also coincides with a bright return of its parent asteroid, 3200 Phaethon and Comet 8P/Tuttle is responsible for the Ursids.
On December 21st at 11:28AM, the Sun sinks to its lowest altitude of the year above the southern horizon. Earth’s axis is tilted away from the Sun and we experience the shortest day and longest night of the year. The December Solstice marks the start of winter in the northern hemisphere and summer in the southern hemisphere. The beginning of winter for the Anishinaabe people in northern Michigan was the full moon after the solstice because time was measured by the Moon. After the sun sinks low in the south, it stands still, then it starts to rise higher. The next full moon marked the start of the New Year which was honored with feasts, songs, dances, and stories.
Morning planets include Venus (-3.8) in Libra, Ophiuchus, and Sagittarius, Mars (+1.7 to +1.5) in Virgo, and Jupiter (-1.5 to -1.6) in Libra. In early December, Mercury and Saturn sink deep into the glow of sunset and rise slightly before the Sun at month’s end. Jupiter rises about 5:30AM EST on the first and an hour earlier on the 31st. Venus rises before dawn early in the month, then sinks deeper into the sunrise during December. Mercury approaches Venus on the 15th and the waning crescent Moon is nearby on the 17th. The Moon approaches Saturn on the 18th and Venus follows on the 25th.
Uranus (+5.7 to +5.8) is in Pisces, and Neptune (+7.9) is in Aquarius. Uranus and Neptune are restricted to the evening skies. They rise mid-day and set in the evening in December. The waxing Moon passes Neptune on the 24th and Uranus on the 27th.
|Sun||Ophiuchus, Sagittarius||-26.8||New Moon||1:30AM EST||12/18|
|Mercury||Sagittarius, Ophiuchus||+0.2 to -0.2||Inferior Conjunction|
|Venus||Libra, Ophiuchus, Sagittarius||-3.8||Mercury 2.2°N|
Saturn 1.1° N
|Mars||Virgo||+1.7 to +1.5|
|Jupiter||Libra||-1.6 to -1.7|
Venus 1.1° S"
|Uranus||Pisces||+5.7 to +5.8|
The New Moon of December is on the 18th at 1:30AM EST. It is the beginning of Lunation 1175 which ends 29.78 days later with the New Moon of Jan. 16th at 10:17PM EST.
The Full Moon of December in Gemini occurs at 10:47AM EST on the 3rd. The December Moon is known as the “Moon before Yule”. The Celts called it the “Cold Moon”, and Colonial Americans called it the “Christmas Moon”. Chinese refer to it as “Bitter Moon”, and it was the “Oak Moon” in Medieval England. Anishinaabe (Odawa and Ojibwe) recognize it as “Manidoo-gizisoons (Little Spirit Moon).
Lunar Perigee (closest to Earth) is 222,135 miles or 56.05 Earth radii on the 4th at 3:43AM EST. Apogee (maximum orbital distance) occurs on the 18th at 8:28PM EST when it is at 252,651 miles (63.75 Earth radii).
The Full Moon is a “Supermoon” because it occurs slightly more than 17 hours before the closest perihelion of the year. Its proximity causes it to be the largest and brightest full moon of 2017, producing the highest tides. Does the Moon also influence the weather? Ocean tides can be as large as 50 feet depending on shoreline configuration, land tides have typical amplitudes of about a foot, and our atmosphere also responds to the tug of the Moon and Sun. Although measured amounts are minuscule compared to other atmospheric disturbances, there is a positive correlation between atmospheric tides and relative humidity (http://onlinelibrary.wiley.com/doi/10.1002/2015GL067342/full). However, correlation is not always cause and effect.
|Planet||Constellation||Magnitude||Moon Passage||Moon Phase||Moon Age|
|Sun||Sagittarius||-26.8||1:30AM EST, 12/18||New||0 days|
|Mercury||Ophiuchus||+2.1||1.7°N, 4:00AM EST, 12/17||Waning Crescent||28.89 days|
|Venus||Ophiuchus||-3.8||4.1°N, 2:00PM EST, 12/17||Waning Crescent||29.30 days|
|Mars||Virgo||+1.6||3.9°NNE, 2:00PM EST, 12/13||Waning Crescent||25.30 days|
|Jupiter||Libra||-1.6||4.1°NNE, 12:00PM EST, 12/14||Waning Crescent||26.22 days|
|Saturn||Sagittarius||+0.4||2.8°N, 9:00AM EST, 12/18||Waxing Crescent||3.13 days|
|Uranus||Pisces||+5.8||4.3°SSE, 4:00PM EDT, 12/27||Waxing Gibbous||9.60 days|
|Neptune||Aquarius||+7.9||1.4°SSE, 9:00AM EST, 12/24||Waxing Crescent||6.31 days|