The December Night Sky

Planets

December is a fairly poor month for viewing the planets. Saturn will be visible for all of December. Jupiter and Mars will be visible for all but the first few days of the month. Venus will be visible for the last few days of the month. Mercury may just be visible for the first part of the month.

Venus will be visible in the evening sky towards the end of the December. By December 22 it sets an hour after the Sun at 21 54 and at 22 01 by month’s end. Venus starts the month in the constellation of Ophiuchus, moving into Sagittarius on December 9. Its magnitude is a constant –3.9.

Saturn will be visible for the last half of the night. At the start of December it rises at 01 23 and at 23 20 by month’s end. Saturn is in the constellation of Leo, in which it remains until September 2009. Its magnitude slightly brightens from 0.4 to 0.3 during the month.

Mercury may be visible in the morning twilight sky at the start of December. At the start of the month it rises one hour before Sunrise at 04 53 and only rises 24 minutes before Sunrise at 05 26 by the end of the month. Mercury starts the month in the constellation of Libra, moving into Scorpius on December 10, into Ophiuchus on December 14 and finally into Sagittarius on December 26. Its magnitude increases from –0.6 to –1.0 during the month.

Mars will be visible after the first few days of the month. By December 14 it rises one hour before Sunrise at 04 42 and at 04 19 by month’s end. Mars starts the month in the constellation of Libra, moving into Scorpius on December 7. Its magnitude slightly increases from 1.6 to 1.5 during the month.

Jupiter will be visible for all but the first few days of December. By December 14 it rises one hour before Sunrise at 04 43 and at 03 48 by month’s end. Jupiter starts the month in the constellation of Libra, moving into Scorpius on December 7 and finally into Ophiuchus on December 30, in which it remains until 2007 December. Its magnitude slightly increases from –1.7 to –1.8 during the month.

All times are for Wellington unless otherwise stated. Other centres may vary by a few minutes.

Phases of the Moon

Full Moon – December 5 at 13:25.
Last Quarter – December 13 at 03:32.
New Moon – December 21 at 03:01.
First Quarter – December 28 at 03:48.


Summer Solstice

The Summer Solstice is at 13 22 on December 22. This is when the Sun is at its most Southerly point in the sky and therefore reaches its maximum altitude for the year at the middle of the day.

Mathematically, the longest day is December 22 and the shortest night is December 22/23. We say mathematically, as the days and nights are longest or shortest by only a few seconds, whereas actual Sunrise and Sunset times can vary by 3 or 4 minutes with the calculated times, due to atmospheric conditions.

After December 22 the length of the day will slowly shorten, although this will hardly be noticed for several weeks.

Diary of Astronomical Phenomena

Dec 2 Moon at perigee (closest to the Earth) at 13:00. (Distance = 0.0024460 AU = 365,920 km).
5 Full Moon at 13 25.
7 Saturn stationary against the background stars at 09 00, as its motion changes from an Easterly to a Westerly direction.
11 Saturn close to the Moon at 00 00.
11 Mercury very close to Jupiter at 05 00.
12 Mars close to Jupiter in the morning twilight.
14 Moon at apogee (furthest from the Earth) at 08:00 (Distance = 0.0027034 AU = 404,420 km).
21 New Moon at 03 01.
22 Summer Solstice at 13 22.
28 Moon at perigee (closest to the Earth) at 15:00. (Distance = 0.0024755 AU = 370,330 km).

DECEMBER SKY CHART

This chart shows the sky as it appears at about 22:00 for ~December 15.

Click to enlarge

How To Use the Sky Charts
To use the sky chart hold it up to the sky so that the direction in which you are looking is at the lower edge of the map. For example, if you are looking at the western horizon then the map should be held so that the “WEST” label is at the lower edge. The altitude and direction of the stars and planets will then be correctly shown. The centre of the chart will be directly overhead.

* Brian Carter is the Senior Astronomer at Carter Observatory (The National Observatory of New Zealand), PO Box 2909, Wellington. (Observatory Web Site: www.CarterObservatory.org)

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