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December 2019 Skies
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by Dick Cookman
Highlights: Comet Journal, Martian Landers, Meteor Showers, Winter Solstice, Planet Plotting, December Moon
Focus Constellations: Pegasus, Pisces, Andromeda, Aries, Perseus, Taurus. Orion, Gemini, Auriga, Camelopardalis, Lynx, Ursa Major, Draco, Ursa Minor, Cepheus, Cassiopeia
Comet C/2017 T2 PanSTARRS is the only 9th magnitude comet in December. It is a long period comet which rose out of the Oort Cloud below the solar system on an orbit tilted at over 60 degrees to the solar system plane. It crossed the plane into northern skies in August and will move westward from Auriga into Perseus this month reaching closest proximity to Earth on Dec. 29. It may brighten to 8th magnitude in February as it approaches perihelion (closest to the Sun) on May 4, 2020 before dropping back through the plane of the solar system in September and embarking on its long journey back to the Oort Cloud.
C/2018 N2 (ASASSN), is an 11th magnitude comet in northern Pegasus in December. It rises in the afternoon and sets in the wee hours. It was at perihelion on November 11, and will slowly move through northern skies for the next two years.
After touching down on Elysium Planita in November, 2018, the Insight lander has made numerous atmospheric and surface measurements, recorded mars quake events, and recently recorded magnetic pulses and oscillations which provide fodder for Earthbound research scientists. Attempts to drill to a depth of 16 feet into Martian soil and place the Heat Flow and Physics Properties Package (HP3) in position to accurately measure heat flow have been unsuccessful to date. Further lab testing on Earth still has to proceed to develop better techniques.
The Curiosity rover is in Glen Torridon, the clay-bearing unit in the valley adjacent to Vera Rubin Ridge on 16,404 foot Mt. Sharp at the center of Gale Crater, the ancient remnant of a massive impact. The rover left Glen Etive, the last drilling site, on Sol 2556 (Oct. 17, 2019) and collected grain size, sedimentary structure, and chemistry data from a series of megaripple features as it traveled. The goal as of Sol 2563 (Oct. 21, 2019) was to approach an area of towering buttes to assess the contact between two geologic units that were first identified from orbit. By the end of October (Sol 2572), Curiosity reached the base of Central Butte after the journey over Glen Torridon which provided copious data about the nature of the underlying rocks and soils. The butte is composed of a series of ledge forming rock layers containing fine bedded laminations in the cohesive pitted mudstones which provided a number of targets for analysis. After completing analysis by Sol 2577 (November 5, 2019), the rover progressed around the base of Central Butte to reach a path permitting partial ascent of the the butte. By Sol 2583 the climb provided access to the base of a steeper slope where there are younger rocks which may have fallen from the top of the butte. After analysis of the rocks was completed, Curiosity descended and turned its attention to Western Butte on Sol 2587 (November 15, 2019). On Sol 2607 (December 4, 2019) the western slope of Central Butte was in the rear view mirror and the rover was well on its way to Western Butte.
Meteor Showers, Asteroid Surprises
Despite interference from the almost full moon, the Geminids may still provide an impressive show because the meteor shower is often accompanied by numerous fireballs. Other showers in December are less impressive unless observers luck out with a surprising display by the Ursids.
- December 2: Chi Orionids. Active Nov. 26-Dec. 15. Radiant 5h28m +23°. ZHR 3. 28 km/sec. Waxing Crescent Moon. Progenitor: Asteroid 2008XM1.
- December 14: Geminids. Active Dec. 7-Dec. 17. Radiant 7h28m +33°. ZHR 120. 35 km/sec. Waning Gibbous Moon. Progenitor: Asteroid 3200 Phaethon.
- December 20: Coma Berenicids. Active Dec. 12-Jan 23. Radiant 11h40m +25°. ZHR 5. 65 km/sec. Waning Crescent Moon. Progenitor: Comet Lowe.
- December 22: Ursids. Active Dec. 17-Dec. 26. Radiant 14h28m +76°. ZHR 10, variable to 50+. 33 km/sec. Waning Crescent Moon. Progenitor: Comet 8P/Tuttle.
On Nov 30, seven meter wide Asteroid 2019 WJ4 passed slightly more than 220,000 kilometers from Earth at 18.5km/s/sec.
The December Solstice occurs on the 21st at 11:19PM EST. For inhabitants of the northern hemisphere, it is the longest night of the year and the shortest day. Since the axis of the Earth is tilted at its maximum angle away from the Sun on the solstice, inhabitants of north polar regions bounded by the Arctic Circle will see continuous night and will see no sunrise while those in south polar regions bounded by the Antarctic Circle will have 24 hour days and no sunset.
The geographic positions of the Arctic and Antarctic circles (and the tropics of Cancer and Capricorn) are established by the angle of tilt of the Earth’s axis relative to the plane of its orbit. The axis angle of 23.5° cycles between 21.5° to 24.5° over a 40,000 year period which changes the latitudes of the these circles.
The Arctic Circle is currently drifting north at about 50 feet per year. The “Torrid Zone” between the two tropics and the Temperate Zones between the Tropics and the Arctic/Antarctic Circles are currently expanding, but unfortunately these trends can’t be blamed for global climate change. The cause is closer to home. We need to look at a much more important phenomenon for a viable explanation. The forward of Walter Kelly’s 1953 “The Pogo Papers” states “we shall meet the enemy, and not only may he be ours, he may be us,” a parody of Commodore Oliver Hazard Perry’s letter to Army General William Henry Harrison after his victory in the Battle of Lake Erie, "We have met the enemy, and they are ours.”
|Planet||Constellation(s)||Magnitude||Planet Passages||Time, Date|
|Sun||Libra, Sagittarius||-26.8||New Moon||12:13AM EST, 12/26|
|Mercury||Libra, Sagittarius||-0.5 to -0.8|
|Venus||Sagittarius, Capricornus||-3.8 to -3.9||Saturn, 1.8°N||Midnight EST, 12/10|
|Mars||Libra||+1.7 to +1.6|
|Jupiter||Sagittarius||-1.7||Solar Conjunction||1:00PM EST, 12/27|
|Saturn||Sagittarius||+0.6 to +0.5||Venus, 1.8°S||Midnight EST, 12/10|
Saturn (+0.6), Venus (-3.8), and Jupiter (-1.7) are lined up as early evening planets in Sagittarius near the southwestern horizon in early December. Jupiter drops into the glare of sunset in the 2nd week of December, and Venus is higher in the sky setting between 6:00 and 7:00PM in December. Saturn is the highest and dimmest of the three and will appear to drop lower in the sky as Venus rises higher during the month. On the 10th, Venus will pass within less than 2 degrees of the ringed planet. Neptune (+7.9) in Aquarius, and Uranus (+5.7) in Aries are higher in the southern and eastern sky respectively. Neptune sets around midnight EST in early December and about 10:00PM at the end of the month. Uranus sets about 4 hours after Neptune.
Mars (+1.7 to +1.6) in Libra is a morning planet which rises about 5:00AM. It will increase slightly in brightness as Earth is catching up to it in orbit. It will reach opposition in October, 2020 when it will be closest to Earth. Mercury (-0.5 to -0.8) was at inferior conjunction in November and is buried in the Sun’s glow all month.
The waxing gibbous Moon is 4.0° from Neptune at 7:00AM EST on the 4th, and 5.0° from Uranus at 6:00AM EST on the 8th. The waning crescent is 4.0° from Mars at 9:00PM EST on the 22nd, and 1.9° from Mercury at 7:00AM EST on Christmas. The waxing crescent Moon is 0.3° from Jupiter at 3:00AM EST on the 26th, 0.9° from Saturn at 7:00AM EST on the 27th, 1.0° from Venus at 9:00PM EST on the 28th, and 4.0° from Neptune at 4:00PM EST on the 31st.
The New Moon of December on the 26th at 12:13AM EST is the beginning of Lunation 1200 which ends 29.66 days later with the New Moon of January on the 24th at 4:42PM EST. The December New Moon is accompanied by an annular solar eclipse visible in the Middle East and southern Asia. Like the Solar Eclipse of 585 BC which was interpreted as an omen and led to a truce in the longstanding war between the Medes and the Lydians, may it bring peace to the Middle East. December’s Full Moon is on the 12th at 12:12AM EST. Commonly known as the “Moon before Yule” or “Long Night Moon”, it was the “Christmas Moon” in colonial times and in Medieval England it was the “Oak Moon.” Celts called it the “Cold Moon” and the Chinese call it the “Bitter Moon”. Anishinaabe (Odawa and Ojibwe) people recognize it as “Manidoo-Giizisoons” (Little Spirit Moon).
Lunar Apogee (maximum orbital distance) occurs on the 4th at 11:08PM EST when the Moon is at 251,311 miles (63.41 Earth radii). Perigee occurs on the 18th at 3:25PM EST when the Moon is at a distance of 230,072 miles (58.05 Earth radii).
|Planet||Constellation||Magnitude||Moon Passages||Moon Phase, Moon Age|
|Sun||Sagittarius||-26.8||12:13AM EST, 12/26||New, 0 days|
|Mercury||Ophiuchus||-0.2||1.9°NNE, 7:00AM EST, 12/25||Waning Crescent, 28.87 days|
|Venus||Capricornus||-3.9||1.0°S, 9:00PM EST, 12/28||Waxing Crescent, 2.87 days|
|Mars||Libra||+1.6||4.0°N, 9:00PM EST, 12/22||Waning Crescent, 26.45 days|
|Jupiter||Sagittarius||-1.7||0.3°ENE, 3:00AM EST, 12/26||Waxing Crescent, 2.78 days|
|Saturn||Sagittarius||+0.6||0.9°S, 7:00AM EST, 12/27||Waxing Crescent, 1.28 days|
|Uranus||Aries||+5.7||5.0°S, 6:00AM EST, 12/8||Waxing Gibbous, 11.93 days|
|Neptune||Aquarius||+7.9||4.0°S, 7:00AM EST, 12/4||Waxing Gibbous, 7.58 days|
|Neptune||Aquarius||+7.9||4.0°S, 4:00PM EST, 12/31||Waxing Crescent, 4.99 days|
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