Mercury remains unsuitably placed for observation for most of December. The planet is currently on the far side of the Sun, passing through superior conjunction on December 8th and staying out of view until the very end of the month. It then re-appears as a difficult early evening object low down above the west-southwest horizon from tropical and southern latitude locations.
For example, on December 31st from latitude 35S (approx. equal to Sydney, Cape Town and Santiago), Mercury shines at mag. -0.8 appearing only 4 degrees above the west-southwest horizon 30 minutes after sunset. Positioned a couple of degrees above Mercury is much more brilliant Venus. From Northern Hemisphere latitudes, the planet is too low down to be seen this month.
Mercury reaches aphelion on December 8th when it's located 0.467 AU (approx. 69.9 million kilometres or 43.4 million miles) from the Sun.
Venus is also an early evening object for observers in the tropics and Southern Hemisphere. It's visibility improves as the month progresses although the planet remains low down above the west-southwestern horizon. However, at magnitude -3.9 it's unmistakable due to its brilliance.
Venus starts the month amongst the stars of Ophiuchus before moving into Sagittarius on December 7th where it remains for the rest of the month. Since the planet is positioned in the southern section of the sky, it's currently not as well placed for observation from northern temperate locations. However, observers at these locations will be able to glimpse it at the very end of the month.
On December 27th, Venus reaches aphelion and is located 0.728 AU (approx. 109 million kilometres or 67.7 million miles) from the Sun.
Mars remains an early evening object during December although it's faded to magnitude +1.1. The planet is moving direct, spending the first few days of the month in Sagittarius before traversing the constellation boundary into Capricornus. From northern locations it sets about 3.5 hours after the Sun, slightly less for those located further south. To the naked eye, Mars appears somewhat like an unremarkable reddish star above the western horizon. Telescopically it appears small; spanning only 5 arc seconds in diameter and even large amateur scopes at high magnifications won't show much detail.
On December 12th, Mars reaches perihelion at a distance of 1.38 AU (approx. 206.6 million km or 128.4 million miles) from the Sun. When opposition occurs around perihelion time - the last occasion in 2003, the next 2018 - Mars appears brilliant. Its magnitude can reach -2.9 with an apparent size of around 25 arc seconds.
Later in the month (Dec. 25th) the waxing crescent Moon passes 6 degrees north of Mars.
Jupiter is located in Leo and continues to increase in brightness and apparent size as it heads towards opposition in February next year. The largest planet in the Solar System rises before midnight at the start of the month, improving by a couple of hours by months end.
During December, Jupiter brightens from magnitude -2.2 to -2.4 and it's apparent size increases from 40 to 43 arc seconds. The planet reaches its first stationary point on December 9th, which signals the start of the 2014-2015 opposition period. Afterwards it begins retrograde motion.
On December 12th, the waning gibbous Moon passes 5 degrees south of Jupiter.
Saturn is currently located amongst the dim stars of Libra. It passed through solar conjunction last month and subsequently re-appears towards the southeast before sunrise during December. The beautiful ringed planet currently shines at magnitude +0.7.
By months end Saturn rises more than 3 hours from the Sun from northern temperate latitudes and only slightly less for those located further south. On December 19th, the waning crescent Moon passes 1.5 degrees north of Saturn.
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. It then reaches its second stationary point on the 22nd - signaling the end of this year's opposition period - after which direct motion is once more resumed. The planet is faintly visible to the naked eye under dark skies but if you can't spot it, it's easy with binoculars.
This month there are two Uranus-Lunar occultations. The first occurs on December 2nd at 00:01 UT and is visible from visible from the Arctic, eastern Alaska and western Canada. The second occurs on December 29th at 04:59 UT, visible from Alaska, northern Canada, Arctic Ocean and northeastern Russia.
Neptune, mag. +7.9, visible with binoculars and small telescopes is moving direct in Aquarius. The most distant planet in the Solar System is positioned a couple of degrees west of Sigma (σ) Aqr (mag. +4.8) and can be seen during the first half of the night.
On December 26th, the almost first quarter Moon passes 4 degrees north of Neptune.
Solar System Data Table December 2014
|Date||Right Ascension||Declination||Apparent Magnitude||Apparent Size||Illum. (%)||Distance from Earth (AU)||Constellation|
|Sun||5th Dec 2014||16h 44m 21.9s||-22d 17m 58.4s||-26.8||32.5'||100||0.986||Ophiuchus|
|Sun||15th Dec 2014||17h 28m 14.9s||-23d 14m 12.4s||-26.8||32.5'||100||0.984||Ophiuchus|
|Sun||25th Dec 2014||18h 12m 36.5s||-23d 24m 20.3s||-26.8||32.5'||100||0.984||Sagittarius|
|Mercury||5th Dec 2014||16h 35m 49.1s||-22d 44m 43.3s||-1.3||04.6"||100||1.448||Ophiuchus|
|Mercury||15th Dec 2014||17h 44m 01.6s||-25d 00m 18.2s||-1.1||04.7"||99||1.438||Sagittarius|
|Mercury||25th Dec 2014||18h 54m 11.8s||-25d 00m 00.3s||-0.8||04.9"||96||1.369||Sagittarius|
|Venus||5th Dec 2014||17h 27m 51.7s||-23d 43m 53.6s||-3.9||10.0"||99||1.677||Ophiuchus|
|Venus||15th Dec 2014||18h 22m 47.6s||-24d 12m 12.4s||-3.9||10.1"||98||1.657||Sagittarius|
|Venus||25th Dec 2014||19h 17m 34.4s||-23d 26m 02.5s||-3.9||10.2"||97||1.633||Sagittarius|
|Mars||5th Dec 2014||20h 09m 06.1s||-21d 30m 56.7s||1.0||05.1"||93||1.846||Capricornus|
|Mars||15th Dec 2014||20h 41m 16.1s||-19d 37m 05.1s||1.1||05.0"||93||1.892||Capricornus|
|Mars||25th Dec 2014||21h 12m 47.9s||-17d 22m 22.3s||1.1||04.8"||94||1.938||Capricornus|
|Jupiter||5th Dec 2014||09h 39m 59.8s||14d 45m 21.0s||-2.3||40.3"||99||4.891||Leo|
|Jupiter||15th Dec 2014||09h 39m 53.8s||14d 48m 22.7s||-2.3||41.5"||99||4.749||Leo|
|Jupiter||25th Dec 2014||09h 38m 31.1s||14d 57m 45.8s||-2.4||42.7"||100||4.622||Leo|
|Saturn||5th Dec 2014||15h 43m 30.6s||-17d 46m 54.0s||0.7||15.2"||100||10.898||Libra|
|Saturn||15th Dec 2014||15h 48m 12.7s||-18d 01m 48.5s||0.7||15.3"||100||10.843||Libra|
|Saturn||25th Dec 2014||15h 52m 43.2s||-18d 15m 21.3s||0.7||15.4"||100||10.763||Libra|
|Uranus||5th Dec 2014||00h 46m 58.6s||04d 18m 19.6s||5.8||03.6"||100||19.499||Pisces|
|Uranus||15th Dec 2014||00h 46m 35.6s||04d 16m 18.4s||5.8||03.6"||100||19.655||Pisces|
|Uranus||25th Dec 2014||00h 46m 31.3s||04d 16m 16.6s||5.8||03.6"||100||19.822||Pisces|
|Neptune||5th Dec 2014||22h 27m 16.7s||-10d 28m 42.6s||7.9||02.3"||100||30.089||Aquarius|
|Neptune||15th Dec 2014||22h 27m 47.3s||-10d 25m 35.8s||7.9||02.3"||100||30.257||Aquarius|
|Neptune||25th Dec 2014||22h 28m 30.0s||-10d 21m 19.5s||7.9||02.2"||100||30.416||Aquarius|