This month’s headliner is the Mars opposition on December 8, when the planet is opposite the sun in our sky, and therefore at a very close approach. November 30 to December 14 marks our closest approach to Mars for another nine years. (The next opposition is in two years, but it won’t be as close.) At this opposition Mars will be about half as far from us as we are from the sun. The planet will be large in telescopes, its polar cap visible.

By a remarkable coincidence, the full moon will block (occult) Mars on December 7. Watch the occultation with the naked eye, binoculars or a telescope as Mars blinks out at 7:45 p.m. and reappears at 8:48 p.m. as seen from Nederland. The planet might flicker as it skims lunar crater edges.

Also in December skies

The sun starts the month in Scorpius, entering Sagittarius December 20. On the shortest day (the 21st), darkness will last nearly 15 hours (14.67 hours) while daylight will be just over nine hours (9.33 hours). Astronomical winter begins at 2:48 p.m. on the 21st, when the sun touches its lowest point on the celestial sphere as seen from Nederland. On December 21 and 22, clock time equals solar time in Nederland with the sun due south at noon on those days.

Activity for school classes: Suspend a plumb bob from a tripod. Snap a chalk line on the bob string’s shadow, across a horizontal slab of concrete, when your watch reads 12:00 on either day. You will have an astronomically surveyed north-south line that you can immortalize with a stripe of spray paint between a pair of duct tape strips bracketing the chalk line. Decorate the line. Discuss with students why clock time usually differs from solar time.

The moon’s dates are: Full (Cold Moon) December 7; Third Quarter December 16; New December 23; First Quarter December 29.

December Meteor Showers: The Geminid shower (associated with asteroid 3200 Phaethon) peaks December 13-15. The Ursid shower (from comet 8P/Tuttle) runs December 17-26, peaking December 22. Stretch out in a lawn chair with a warm drink and warm clothing to see these showers. Lack of moonlight will make for good viewing this year.

Best Sky Viewing Nights (Minimal Moon): December 16-30.

Sunset (Mid-Month): The Pleiades rise in the east with red Aldebaran just below and Mars closely following. Brilliant Capella rises in the northeast. The Andromeda Galaxy is high in the northeast, presenting a nice binocular view. Reddish Fomalhaut is low in the south. Deneb, Vega and Altair form a bright triangle high in the northwest to west.

Midnight (Mid-Month): The Gemini twins Castor (above) and Pollux (below) are nearly overhead in the northeast. Orion is due south with Sirius below and to the left. M42, the Great Nebula in Orion’s sword, is visible to the naked eye; it presents a terrific view in binoculars and low-power telescopes. Taurus with the Pleiades is nearly overhead.

Sunrise (Mid-Month): Vega is low in the northeast. Reddish Arcturus is high in the east. The Orangish Regulus in Leo is almost overhead, slightly offset toward the southwest. The Gemini Twins Castor and Pollux are close to setting in the west. Capella is set in the northwest.

Mercury is visible low in the west, in Sagittarius, at sunset between December 19-28. Best viewing is the 21st–24th. In Nederland, the west end of the reservoir affords a clear horizon.

Venus is mostly lost in the sun’s evening glare. It becomes barely visible, low in the west, at month’s end.

Mars rises in the ENE near sunset, in Taurus. Mars pairs nicely near reddish Aldebaran. Mars moves backward (retrograde) this month against the stars. “Retrograde” is an optical illusion caused by our own motion, not Mars’, as we speed past the planet on the inside orbital track.

Jupiter is high and bright in the south, in Aquarius, at sunset. It sets at about midnight. Its increasing distance gives it a small apparent size in telescopes.

Saturn is low in the SSW at sunset. It sets before 9 p.m.

Notable Space Missions: On December 11 the Orion deep-space capsule, with three instrumented mannequins on board, returns from the moon and uses the world’s largest composite heat shield to re-enter Earth’s atmosphere. Splashdown and recovery will be west of San Diego. This will conclude the Artemis I mission, a six-week uncrewed moon-orbiting trip paving the way for planned US crewed moon landings in the next few years. Coincidentally, December 14 marks 50 years since the last astronauts left the moon. On December 16 South Korea’s Danuri probe enters lunar orbit for a science mission.

Frank Sanders is a spectrum scientist with the U.S. Dept. of Commerce in Boulder. He takes astronomy-related inquiries at backyardastronomy1@gmail.com.