| December is the twelfth month in the Gregorian Calendar and consists of 31 days. The name of December is derived from the Latin ‘decem’ meaning ten. December was the tenth month when the year used to start on March 1. |
Winter begins on December 21st when the Winter Solstice occurs. The Winter Solstice occurs when the tilt of the Earth is pointed directly away from the Sun. This point marks the beginning of Winter. The Winter Solstice has the shortest amount of daylight and the longest night.
The New Moon for December occurs on Wednesday, December 16th, which will make the weekends on December 12th – 13th and Decemeber 19th – 20th as both good weekends for dark sky observing.
There are two Full Moons in December. The first Full Moon occurs on December 1st and is known as the “Full Cold Moon”, “Long Night Moon” or the “Moon Before Yule.” The second Full Moon occurs on December 31st and is known as the “Full Wolf Moon”, “Old Moon” or “Moon After Yule.”
Because the December 31st Full Moon is the second Full Moon in the calendar month it is also known as a “Blue Moon” by the “Sky and Telescope Rule”. Also the December 31st Full Moon brings an Umbral Lunar Eclipse visible from Australia, Asia Europe and Africa.
The above movie shows the Umbral Eclipse on December 31st as view from India. Each frame is one minute.
The above movie shows the Umbral Eclipse on December 31st as view from the Moon. Each frame is one minute.
Mercury is found in the evening in December. Mercury begins the month in the constellation Ophiuchus (The Serpent Bearer), and on December 3rd, moves into the constellation Sagittarius (The Archer).
Mercury reaches its Greatest Western Elongation on December 18th.
This date provides the Best Evening Views of Mercury as it will be
20°17’47” from the Sun, setting about one hour, 20 minutes after Sunset.
Mercury disappears into the glare of the sunset by December 31st.
| Venus is observable in the morning hours of December until December 18th when it disappears into the glare of Sunrise. |  |
Venus begins the month in the constellation Libra (The Balance) until December 3rd when it moves into the constellation Scorpius (The Scorpion). On December 7th, Venus moves into the constellation Ophiuchus (The Serpent Bearer) where it will remain until December 22 when it moves into the constellation Sagittarius (The Archer).
Mars can be observe from the late evening hours until morning all month in the constellation Leo (The Lion). Mars rises around 10:40 pm (PST) at the beginning of December and by the end of the month Mars rises around 8:50 pm (PST).
On December 20th Mars starts retrograde motion. The above movie shows the path of Mars during the month of Decemeber. Each frame is one sideal day.
Located in the constellation Capricorn until January 2010, Jupiter is visible during the evening hours of December. Jupiter sets around 11:00 pm (PST) at the start of December and by the end of the month Jupiter sets around 9:30 pm (PST).
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On December 20th, Jupiter passes within 0°31’ from Neptune and sets less than 5°40’ from the Waxing, Crescent Moon. |
Saturn rises in the very early morning hours of December; rising around 2:25 am (PST) at the start of the month and by the end of the month rising around 12:35 am (PST). Saturn is located in the constellation Virgo (The Maiden) until December 2012.
| On December 10th the Waning, Crescent Moon sets less than 8° from Saturn. |  |
Uranus is visible until the early morning hours of December. It sets around 1:25 am (PST) at the beginning of December and at the end of December is sets around 11:35 pm (PST). Uranus is located in the constellation Aquarius (The Water Bearer) until January 2010.
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The waxing, Crescent Moon passes with 5°15’ of Uranus on December 23rd. |
Neptune can be observe during the evening hours of December At the start of the month Neptune sets around 11:15 pm (PST) and by the end of the month Neptune sets around 9:20 pm (PST). Neptune is found in the constellation Capricornus (The Sea Goat) until the year 2010
| On December 20th, Jupiter passes within 0°31’ from Neptune and sets less than 5°40’ from the Waxing, Crescent Moon. | |
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Pluto may be observed around the first week of December and around December 9th Pluto disappears into the glare of the Sunset. |
Pluto is located in the constellation Sagittarius (The Archer) until the year 2023.
12/1/2009 Full Cold Moon
12/8/2009 Last quarter Moon
12/9/2009 Pluto disappears into the glare of the evening Sun.
12/10/2009 Saturn sets less than 8° of waning, crescent moon
12/16/2009 New Moon
12/18/2009 Mercury’s Greatest Eastern Elongation - Best evening view ( 20°17′47″ )
12/18/2009 Venus disappears into the glare of the sunrise, ending its reign as the Morning Star
12/20/2009 Mars begins retrograde motion
12/20/2009 Jupiter and Neptune in conjunction with each other passing less than 0°31 of each other.
12/20/2009 Jupiter sets within 5°40′ of waxing, crescent moon
12/21/2009 Winter Solstice - The longest night
12/23/2009 A waxing, crescent moon passes within 5°15′ of Uranus
12/24/2009 First Quarter Moon
12/31/2009 Full Wolf Moon - Also “Blue” Moon by “Sky & Telescope” Rule
12/31/2009 Umbral Lunar Eclipse visible from Australia, Asia, Europe and Africa
12/31/2009 Mercury disappears into the glare of the evening Sun.
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