Mercury reached greatest western elongation last month (Nov. 18th) and was visible for most of November just before sunrise from northern temperate and tropical latitudes. With an orbital period of only 88 days, Mercury takes little time in switching between greatest elongation (east or west) and conjunction (superior or inferior). In December, superior conjunction arrives, which the planet passes through on the 29th. Although the planet is too close to the Sun to be visible at superior conjunction it may still be glimpsed from the tropics and northern temperate latitudes as an early morning object rather low down in the sky before dawn during the first week of December (mag -0.7). For Southern Hemisphere observers, Mercury is inconveniently placed for observation during this time.
On December 1st, the thin waning crescent Moon passes only 0.4 degrees north of Mercury. Three weeks later on the 22nd, Mercury reaches aphelion at a distance of 0.467 AU (approx. 69.9 million km or 43.4 million miles) from the Sun.
From the tropics and Southern Hemisphere Venus remains a spectacular evening object during the first half of the month. From these latitudes, Venus sets over 3 hours after the Sun at the start of December decreasing slightly to 2.5 hours by the middle of the month. Northern Hemisphere observers have not had it so good during this apparition. However, during December the planet is also a lovely sight, low in the southwest sky at dusk from these latitudes.
Only during the second half of December does Venus draw rapidly in towards the Sun and consequently the period of visibility noticeably shortens. By the end of the month the planet has faded from a peak magnitude of -4.8 to -4.4. The phase of Venus decreases from 31% to 4% During December.
The waxing crescent Moon passes 8 degrees north of Venus on December 6th.
Mars remains an early morning object in December. The planet continues to improve in brightness, apparent size and visibility as it continues direct motion through the constellation of Virgo. At the start of December, the "Red planet" shines at magnitude +1.2 with an apparent size of 5.6 arc seconds. By month's end its brightness has increased by nearly half a magnitude to +0.8, with the apparent size increasing slightly to 6.8 arc seconds. Telescopically, the apparent size of Mars is still relatively small but amateur astronomers with medium size scopes or better should be able to spot some of the planets more prominent markings.
What's noticeable, especially to the naked eye, is the brighter Mars becomes the more apparent its deep red-orange hue. Mars is also the easiest planet to monitor movement against the "fixed" background stars.
By the end of December, Mars rises an hour or so after midnight and on December 26th, the last quarter Moon passes 5 degrees south of Mars.
Jupiter is now a spectacular sparkling object moving retrograde amongst the stars of Gemini. The planet rises in the east just after sunset and remains visible for the rest of the evening. During December, it brightens slightly from magnitude -2.6 to -2.7 with its apparent size increasing marginally from 45 to 47 arc seconds.
Jupiter current location favours Northern Hemisphere observers since the planet is located in the northern section of the sky. From Southern Hemisphere latitudes, Jupiter appears closer to the horizon, but still unmistakable due to its brilliance.
Telescopically the planet is a gem. Even a small instrument shows the main cloud belts. Through a medium or large sized telescope a wealth of additional detail is visible. Also easily seen, but not always at the same time are Jupiter's four brightest moons, Io, Europa, Ganymede and Callisto.
On December 19th, the almost full Moon passes 5 degrees south of Jupiter.
Saturn, mag +0.8, was at solar conjunction early in November before reappearing in the morning sky at the very end of the month. It's now visible towards the east-southeast before dawn. By the end of December, the famous "jewel" of a planet rises some 4 hours before the Sun from northern temperate latitudes and only slightly less from locations further south.
Saturn is currently located in Libra and on December 1st and December 29th the thin waning crescent Moon passes 1 degree south of the planet.
Uranus, mag +5.8, is now two months past opposition but still remains well placed for observation. During December, the seventh most distant planet from the Sun is visible as soon as it's dark enough until after midnight.
Uranus starts December moving retrograde in Pisces, before crossing into neighbouring Cetus on December 12th. The planet then reaches its second stationary point on December 18th - signaling the end of this year's opposition period - after which direct motion is once more resumed. The next day, Uranus moves back into Pisces where it remains for the rest of the month.
On December 11th, the waxing gibbous Moon passes 3 degrees north of Uranus.
Neptune, mag. +7.9, is located in Aquarius and is visible during the first part of the night. It's positioned almost 3 degrees west of Sigma (σ) Aqr (mag. +4.8) and 3 degrees south of Ancha (θ Aqr - mag. +4.2).
On December 8th, the first quarter Moon passes 6 degrees north of Neptune.
Solar System Data Table December 2013
|Date||Right Ascension||Declination||Apparent Magnitude||Apparent Size||Illum. (%)||Distance from Earth (AU)||Constellation|
|Sun||5th Dec 2013||16h 45m 29.1s||-22d 19m 58.4s||-26.8||32.5'||100||0.986||Ophiuchus|
|Sun||15th Dec 2013||17h 29m 24.0s||-23d 15m 04.3s||-26.8||32.5'||100||0.984||Ophiuchus|
|Sun||25th Dec 2013||18h 13m 44.4s||-23d 24m 00.2s||-26.8||32.5'||100||0.984||Sagittarius|
|Mercury||5th Dec 2013||15h 50m 28.9s||-19d 17m 50.0s||-0.7||05.1"||93||0.698||Libra|
|Mercury||15th Dec 2013||16h 54m 57.9s||-22d 58m 51.9s||-0.8||04.8"||98||0.918||Ophiuchus|
|Mercury||25th Dec 2013||18h 03m 09.1s||-24d 48m 14.9s||-1.2||04.7"||100||1.159||Sagittarius|
|Venus||5th Dec 2013||19h 44m 01.8s||-23d 54m 06.2s||-4.8||39.7"||28||0.420||Sagittarius|
|Venus||15th Dec 2013||20h 00m 47.6s||-21d 45m 57.9s||-4.7||46.8"||19||0.357||Sagittarius|
|Venus||25th Dec 2013||20h 02m 07.5s||-19d 36m 46.1s||-4.6||54.7"||10||0.305||Sagittarius|
|Mars||5th Dec 2013||11h 56m 50.3s||02d 23m 48.5s||1.2||05.8"||91||1.627||Virgo|
|Mars||15th Dec 2013||12h 15m 42.0s||00d 27m 57.8s||1.1||06.1"||91||1.532||Virgo|
|Mars||25th Dec 2013||12h 33m 36.9s||-01d 20m 46.5s||1.0||06.5"||90||1.434||Virgo|
|Jupiter||5th Dec 2013||07h 22m 31.9s||22d 08m 30.8s||-2.6||45.3"||100||4.354||Gemini|
|Jupiter||15th Dec 2013||07h 18m 14.4s||22d 18m 11.7s||-2.7||46.1"||100||4.278||Gemini|
|Jupiter||25th Dec 2013||07h 13m 04.1s||22d 28m 59.2s||-2.7||46.6"||100||4.229||Gemini|
|Saturn||5th Dec 2013||15h 02m 12.1s||-14d 58m 55.1s||0.8||15.5"||100||10.755||Libra|
|Saturn||15th Dec 2013||15h 06m 33.7s||-15d 16m 16.2s||0.8||15.6"||100||10.672||Libra|
|Saturn||25th Dec 2013||15h 10m 38.6s||-15d 31m 48.5s||0.8||15.7"||100||10.567||Libra|
|Uranus||5th Dec 2013||00h 32m 11.4s||02d 42m 28.8s||5.8||03.6"||100||19.590||Pisces|
|Uranus||15th Dec 2013||00h 31m 56.3s||02d 41m 17.2s||5.8||03.6"||100||19.751||Cetus|
|Uranus||25th Dec 2013||00h 32m 00.1s||02d 42m 07.2s||5.8||03.5"||100||19.921||Pisces|
|Neptune||5th Dec 2013||22h 18m 55.0s||-11d 12m 37.2s||7.9||02.3"||100||30.141||Aquarius|
|Neptune||15th Dec 2013||22h 19m 28.9s||-11d 09m 17.2s||7.9||02.3"||100||30.307||Aquarius|
|Neptune||25th Dec 2013||22h 20m 14.6s||-11d 04m 50.3s||7.9||02.2"||100||30.464||Aquarius|