SKY REPORTER: December 2011 main content.

SKY REPORTER: December 2011

by Steve Beyer on


Sky Data

Thursday December 1st, civil twilight begins at 6:30 a.m. Eastern Standard Time and sunrise is at 7:00 a.m. That evening the sun, located in the constellation Ophiuchus, sets at 4:29 p.m. civil twilight concludes at 4:59.

Civil twilight starts at 6:41 a.m. and sunrise is at 7:12 on Thursday, December 15th. That day sunset occurs at 4:29, with civil twilight concluding at 5 p.m.

On the last day of the month, Saturday December 31st, civil twilight begins at 6:49 with sunrise at 7:20. Sunset is at 4:38 and civil twilight ends at 5:09.

During December average overnight temperatures recorded in Central Park drop from 36 degrees Fahrenheit on the first of the month, to 28 degrees on the 31st. On that day the Sun is located in the constellation Sagittarius.

Principal Phases of the Moon this month are:

First Quarter December 2
Full Moon December 10
Last Quarter December 17
New Moon December 24

Winter begins in the northern hemisphere at 12:30 a.m. the early morning of December 22nd. That time the sun is directly above a point in the Indian Ocean, 1,300 miles west north-west of Perth Australia and 1,330 miles south south-west of Jakarta, Indonesia.

Sky Cast

At the conclusion of civil twilight the evening of December 1st, Mercury has just set and the nearly First Quarter moon is half way between horizon and zenith in the southern sky. Venus is ten degrees of arc above the southwestern horizon and sets at 6:14 p.m. Jupiter is towards the east, 27 degrees above the horizon, at the border between constellations Pisces and Aries. Mars rises in Leo at 11:24 p.m. Saturn is Virgo, rising at 3:19 during the morning of December 2nd.

In early evenings at the start of December comet Garradd remains in Hercules, low in the western sky. Its softly diffused 6th magnitude glow is visible with low magnification telescopic eyepieces under a dark sky, but does not provide contrast with milky appearing skies over urban areas.

The evenings of Monday and Tuesday December 5th and 6th the bright gibbous moon is in the neighborhood of Jupiter, still extraordinarily bright at magnitude minus 2.8.

On the night of Saturday the 10th the Full Moon is located in Taurus, among bright stars and constellations typical of winter evenings. During December the Full Moon is above the horizon longer than at other times of the year, and it crosses the meridian at a higher altitude.

During early morning Saturday December 17th the Last Quarter moon may be seen nine degrees of arc south of Mars. The Red Planet then has magnitude 0.5, equivalent to some of the brightest stars in our sky.

On December 20th the waning crescent moon’s disk is about 23% illuminated by sunlight as seen from Earth. The lunar crescent is then about eight degrees south of Saturn.

You might ask if the moon’s Last Quarter phase occurred three days earlier, on Saturday the 17th, why does the moon’s disk appears nearly one-quarter illuminated on Tuesday the 20th. This is because what we call “Last Quarter” phase occurs when the moon starts the last quarter of its phase cycle, from one New Moon to the next. The designation Last Quarter doesn’t indicate the percentage of lunar surface seen illuminated by sunlight.

Lunar Phases Diagram
Cycle of Lunar Phases.

At about 6:45 the morning of Thursday December 22nd a thin crescent moon might be seen in the southeast, nine degrees of arc to the upper right of Mercury shining at magnitude minus 0.34, and 10 degrees above first magnitude Antares, brightest star in the constellation Scorpius.

About five p.m. at the end of civil twilight December 26th the very thin (6% illuminated) waxing crescent moon is eight degrees of arc to the right of brilliant Venus. At that time both are 20 degrees of arc above the southwestern horizon. The next evening a wider lunar crescent is nine degrees above Venus as twilight ends.

On New Year’s Eve at five p.m., Venus is well above the horizon at an altitude of 20 degrees. It has its usual brilliance with a magnitude of minus four, and sets at 7:19 p.m.

As we are preparing to welcome the year 2012 on the evening of December 31st, Mars rises at 10:17 p.m. Later, as many are heading home after the night’s celebrations, Saturn rises at 1:34 a.m. and Jupiter sets at 1:53 a.m.

Sky Lore

With the advent of the holiday season, magnificent stars in and around the constellation Orion are well placed for evening viewing. The brightest members of this celestial congregation include Betelgeuse and Rigel in Orion, the Hunter; Aldebaran in Taurus, the Bull; Capella in Auriga, the Charioteer; Procyon in Canis Minor, the Little Dog; and the most brilliant star in our entire night sky, Sirius in the constellation of the Large Dog, Canis Major.

This array is placed conveniently above the eastern and southern horizons by 10 p.m. at the start of December and by eight p.m. at month’s end.

Orion Constellation Sky Photo
Stars of Orion.

Each of these extraordinary stars catch our attention, and the pattern of three second magnitude, nearly equally spaced stars along a line tracing the mythological “Belt of Orion, is an unmistakable sky feature at this time of the year. Once you notice these three, nearby Betelgeuse just to their northeast and Rigel to the southwest help orient our views to bright stars in neighboring constellations. For example, follow the line of the Belt stars to the northwest toward first magnitude Aldebaran. Look along the Belt to the southeast and you arrive at Sirius. A line from Sirius through Betelgeuse aims your gaze toward Capella. The view from Rigel toward Betelgeuse helps identify Castor and Pollux, brightest stars in Gemini.

Orion was depicted in classical mythology as a great Hunter, whose stellar representation is poised ready to ward off the charge of Taurus, while his two hunting dogs Canis Major and Canis Minor are arrayed nearby.