December, the twelfth month, is named after ‘decem’ the Latin word for tenth. In case you’re wondering how this apparent discrepancy came about, the Roman calendar, whose names for months was carried over to our own, started in March.

Focus on the planets

Mercury may be spotted low in the southwest at dusk during the last half of the month. The best time to view Mercury by telescope will be Christmas Eve and the evening of Christmas Day.

Venus blazes on the east-southeast horizon three hours before sunrise as December opens. Venus will appear as a thickening crescent but overall will shrink in size as the planet recedes from Earth.

Mars is located to the immediate upper right of Venus but proves to be a dim companion for its brilliant neighbor.

Jupiter rises shortly after 10:00 p.m. and is well up on the eastern horizon by midnight. Castor and Pollux, the twin stars of Gemini, are located directly above Jupiter.

Saturn is located well up on the eastern horizon where it will be visible from dusk to dawn by midmonth. Saturn will be at its biggest and brightest during December while its ring system heads towards the most favorable tilt for viewing in years.

Uranus is located on the eastern edge of Capricornus, where it can be seen with binoculars. Uranus is slowly descending on the western horizon and will be lost in the evening twilight later in the month.

Neptune is located in the southwest to the right of Uranus in Capricornus.

Our celestial neighborhood

J.B.S. Haldane once remarked that, “Not only is the universe stranger than we suppose, but stranger than we can suppose.” Nothing could be stranger than a titanic explosion picked up by orbiting satellites in 1997. It came from the edges of the universe, over 12 billion light-years away, and took place not long after the universe came into being through the Big Bang. The satellites picked up gamma rays that cannot penetrate to surface detectors, but it was the sheer enormity of the explosion that took astronomers’ breath away. In a few seconds, more energy was released than the sun will produce in its 10 billion-year lifetime! Since then many other “gamma ray bursters” have been discovered and astronomers are at a loss to explain their origin. One explanation is that a supermassive star undergoes a catastropic collapse and forms a black hole rather than a neutron star. Another that it may come from a collison between two black holes. Until more data is collected these gigantic bursts will remain one of many mysteries in the universe.

December events

1 Sunrise, 6:52 a.m.; sunset, 3:56 p.m. Look to the southeastern horizon at dawn where the crescent moon, Venus, and Mars form a tight grouping. The bright star to the group’s upper right is Spica.

2 Moon at perigee or closest approach to the Earth.

4 New moon, 2:35 a.m.

8 Fomalhaut, alone on the southwest horizon, can be seen well to the left of the moon tonight.

11 Moon in first quarter, 10:49 a.m.

13 St Lucy’s Day, once considered to be the middle of winter. The Geminid meteor shower can be seen over the next several nights. Look for them to originate in the vicinity of Castor in Gemini with a possible density of 120 per hour.

14 Moon at apogee or greatest distance from the Earth.

17 The moon is above orange Aldebaran tonight with Saturn to their lower left.

18 Sun enters Sagittarius on the ecliptic.

19 Full moon, 2:11 p.m. The full moon of December is called the Moon Before Yule or the Full Cold Moon.

21 Winter solstice, 8:14 p.m. This marks the official start of winter when the sun is at its furthest point south of the celestial equator.

22 The sun enters the astrological sign of Capricornus but, astronomically, has just entered Sagittarius. Look to the east for the waning moon with Jupiter directly beneath it.

25 Merry Christmas!

30 The moon is at perigee for the second time in December. Venus shines above the crescent moon in the southeast at dawn. Mars is to the right of Venus.

31 Sunrise, 7:13 a.m.; sunset, 4:04 p.m.