THE SOLAR SYSTEM IN DECEMBER 2017
Dates and times shown are NZDT (UT + 13 hours) unless otherwise stated. Times are for Wellington. They will vary by a few minutes elsewhere in NZ.
The southern summer solstice is on December 22 with the Sun appearing furthest south at 5.28 am, about 12 minutes before sunrise at Wellington.
December 1 NZDT December 31 NZDT
SUN: rise 5.40am, set 8.39pm rise 5.47am, set 8.59pm
Twilights morning evening morning evening
Civil: start 5.10am, end 9.10pm start 5.17am, end 9.31pm
Nautical: start 4.28am, end 9.52pm start 4.34am, end10.14pm
Astro: start 3.40am, end10.41pm start 3.42am, end11.05pm
DECEMBER PHASES OF THE MOON (times NZDT, as shown by GUIDE)
Full moon: December 4 at 4.47am (Dec 3, 15:47 UT)
Last quarter December 10 at 8.51pm (07:51 UT)
New moon: December 18 at 7.30pm (16:30 UT)
First quarter: December 26 at 10.20pm (09:20 UT)
THE PLANETS in DECEMBER 2017
Of the five naked eye planets only Mars and Jupiter will be far enough from the Sun for viewing and they are in the morning sky. Mars will be the better placed, especially early in the month.
Mercury, Venus and Saturn are all close to the Sun and at best make difficult objects. Mercury and Saturn are in the early evening sky at the beginning of December but reach conjunction during the month.
MARS starts December in Virgo rising more than two hours before the Sun. On the 1st it will be 3° below Spica, the planet being the fainter object at magnitude 1.7 compared to Spica's 1.1. On the 21st Mars will cross into Libra. By the 31st it will rise 3 hours before the Sun
During December Mars will be catching up with Jupiter, they are 16° apart on the 1st but only 3° apart on the 31st.
JUPITER is in Libra all month. It rises just over 80 minutes before the Sun on the 1st. This is close to the start of nautical twilight so Jupiter will not be an easy object low in the twilit sky. By the end of December Jupiter rises more than 3 hours before the Sun, only 9 minutes after Mars. The two planets will be more than 20° up an hour before sunrise, Jupiter more than 3 magnitudes brighter than Mars.
The crescent moon will be some 5° below Mars on the morning of the 14th and a similar distance from Jupiter the following morning, also Vesta will be less than a degree to the right of the moon.
MERCURY starts the month as an evening object setting nearly 2 hours after the Sun. 45 minutes after sunset, Mercury at magnitude 0.0 will be 8° above the horizon towards the west-south-west. On the 3rd of December, the planet is stationary, after which it starts moving to the west towards the Sun which itself will be moving to the east. Their separation will decrease rapidly over the next few days until Mercury is at inferior conjunction with the Sun on the 13th. At conjunction Mercury will pass 1.5° north of the Sun.
After conjunction Mercury will be a morning object. By the end of the month it will rise 85 minutes before the Sun, so will be a very low object a little to the south of east as the sky brightens.
SATURN will also finally disappear from the evening sky during December. On the 1st it will be nearly 3° to the lower right of Mercury, making Saturn even more difficult to see. It is at conjunction with the Sun on the 22nd. After conjunction it too becomes a morning object but will be too low for easy observation rising only half an hour before the Sun on the 31st.
VENUS is close to the Sun all month. It rises 28 minutes before the Sun on the 1st. This reduces to only 11 minutes earlier on the 31st.
URANUS is in Pisces during December. It is well placed in the evening sky once it is dark. It sets about 1.45 am at the end of December.
NEPTUNE is also an evening object setting about 100 minutes before Uranus. So at the end of December it sets just after midnight. The planet is an Aquarius at magnitude 7.9.
PLUTO, magnitude 14.5, remains in Sagittarius. By the end of December it sets only have an hour after the Sun.
BRIGHTEST MINOR PLANETS
(1) CERES is a morning object in Leo, brightening from magnitude 8.1 to 7.5 during the month.
(2) PALLAS is in Fornax during December. It dims a little from magnitude 8.4 to 8.7 during the month.
(4) VESTA is in Libra during December quite close to Jupiter. At their closest on December 11, Vesta will be about 4° from the gas giant. Vesta at magnitude 8 will rise two and a half hours before the Sun on the 31st.
(7) IRIS dims from magnitude 7.8 to 8.6 during December. The asteroid is an evening object in Aries.
(8) FLORA is a morning object brightening from magnitude 9.1 to 8.3 during December. It is in Gemini two days short of opposition on the 31st.
(20) MASSALIA starts December in Orion at magnitude 9.0. It crosses into Taurus on the 11th, reaches opposition on the 17th with a magnitude 8.4 and fades to 8.9 by the end of the month. It is in the sky most of the night.