The Solar System In December 2016
Dates and times shown are NZDT (UT + 13 hours).
Rise and set times are for Wellington. They will vary by a few minutes elsewhere in NZ.
Sunrise, sunset and twilight times in December
December 1 NZST December 31 NZDT morning evening morning evening SUN: rise: 5.39am, set: 8.40pm rise: 5.47am, set: 8.59pm Twilights Civil: starts: 5.10am, ends: 9.11pm starts: 5.17am, ends: 9.31pm Nautical: starts: 4.28am, ends: 9.52pm starts: 4.34am, ends:10.14pm Astro: starts: 3.40am, ends:10.41pm starts: 3.43am, ends:11.05pm
December phases of the moon (times as shown by guide)
First quarter: December 7 at 10.03 pm (09:03 UT) Full moon: December 14 at 1.06 pm (00:06 UT) Last quarter December 21 at 2.56 pm (01:56 UT) New moon: December 29 at 7.53 pm (06:53 UT)
The SOUTHERN SUMMER SOLSTICE is on 2016 December 21 at 11.45 pm NZDT (10:45 UT)
The planets in December 2016
Venus remains the most obvious planet in the evening sky. Mars, much fainter, is higher in the sky. Mercury May be briefly visible low in the evening sky about an hour after sunset. It will disappear after about mid month. Jupiter is the only planet visible in the morning sky. Saturn is not likely to be seen during December.
Mercury starts December as an evening object with a magnitude -0.5. On the 1st it will set nearly 100 minutes after the Sun. An hour after sunset, shortly before the end of nautical twilight, the planet will be 5° up in a direction 30° to the south of west. Venus will be some 25° away to its upper right.
Throughout the first half of December Mercury will continue to set up to 100 minutes after the Sun. It reaches its greatest elongation, 21° east of the Sun, on the 11th. After mid December the distance of Mercury from the Sun starts decreasing, so it sets earlier. As a result it will be lost in the evening twilight within a few days. The planet is at inferior conjunction between the Earth and Sun on December 29, when it will be 101 million km, 0.675AU, from the Earth and 0.311AU from the Sun.
Venus will remain a brilliant light in the evening sky throughout December reaching magnitude -4.4. It sets shortly before midnight throughout the month. The planet starts December in Sagittarius but, moving to the east, crosses into Capricornus on the 7th. By the 31st Venus will have moved crossed to the eastern edge of the constellation.
The crescent moon will be 6.5° from Venus on the evening of December 3.
Mars starts December in Capricornus at magnitude 0.6. With a distinctly orange colour it will be some 25° to the upper right of Venus. On December 3 Mars passes close to the star iota cap (mag 4.3). They will be closest about 9.30 pm, some 50 minutes after sunset in Wellington, when only 40 arc-seconds apart. about 1% of the moon's diameter. At this distance they will be almost impossible to separate by eye, but fairly easy to do so using binoculars. By midnight Mars will have moved to be just over 4 arc-minutes from the star
Two days later the crescent moon will be 3.5° from Mars.
In mid December Mars moves into Aquarius. It movement across the constellation will be slower than Venus's in Capricornus, as a result the two will be only 12° apart on the 31st. On that evening Mars will have almost caught up Neptune, their separation being some 40 arc-minutes.
Jupiter remains the only one of the naked eye in the December morning sky. On the 1st it rises at 3.15 am, advancing to about 1.30 am by the 31st. The planet is in Virgo, its distance from Spica decreasing from 8 to 4.5° during the month.
On the morning of the 23rd, the moon a day past third quarter, will be just over 3° from Jupiter.
Saturn is at conjunction with the Sun on December 10 so will not be observable during December. At conjunction Saturn will be 1650 million km, 11 au, from the Earth, 10 AU beyond the Sun. By the end of the month it will rise in the morning sky about 75 minutes before the Sun.
Uranus, at magnitude 5.7, remains in Pisces and is observable all evening. It sets close to 3.30 am on the 1st and two hours earlier on the 31st. The planet is stationary on the 30th. As a result its position changes very little during December, by a distance equivalent to only two-thirds of the diameter of the full moon.
Neptune is in Aquarius at magnitude 7.9 throughout December. It sets about 2 am on the 1st, and midnight at the end of December. The moon is closest to Neptune on the 6th but still 6° at midnight. A few hours later the moon will occult the planet as seen from the northern Atlantic region including northeast Canada and much of Greenland. Mars will close in on Neptune during December.
Pluto at magnitude 14.5 is very low in the early evening sky. It is in Sagittarius setting only 20 minutes after the Sun by the end of December.
(1) Ceres continues in Cetus during December with its magnitude fading from 8.2 to 8.6. It is stationary mid month resulting in most of its apparent motion being to the north so ending the month some 7° from Uranus.
(18) Melpomene is also in Cetus between 9 and 11 degrees from Ceres. The asteroid, diameter 148 km, fades from magnitude 8.9 to 9.6 during December. Melpomene is on the opposite side of Ceres to Uranus.
Both Ceres and Melpomene are visible all evening not setting until well after midnight.
(4) Vesta is in Cancer throughout December rising about 12.15 am on the 1st and two hours earlier on the 31st. Its magnitude brightens from 7.4 to 6.7 during the month. Vesta starts December 2° from the Beehive cluster, M44. Its westerly retrograde motion sees the asteroid move away from the cluster so that by the 31st they will be 5 degrees apart.
Brian Loader New Zealand