November 22, 2021

AstroCal – December 2021


     We will begin this month’s tour of astronomical happenings with the planets visible in the south-southwest and southwestern sky at dusk.  The brightest is Venus (magnitude – 4.7 on Dec 1 and -4.4 Dec 31) and located closest to the horizon to the lower right of Jupiter (mag. -4.7) and Saturn (mag. +1.5).  All three will be visible throughout the month with faint Mercury joining Venus late in the month when it will appear below and to the right of its’ closest planetary neighbor.  In the last few days of 2021, Mercury will pass just 4.2 degrees below Venus as The Winged Messenger moves away from the The Veiled Planet in a southerly direction.

     Viewed with binoculars or a small spotting scope, Venus will appear as a thin crescent which will reduce from 15% (of the full planetary width) on Dec 16 to 10 percent on Dec 21 and only 5 percent on Dec 27.  The best time to view the crescent with binoculars is when the sky is still bright and blue.  After dark, the contrast between the bright planet and the sky is too great for one to see the crescent shape.

     Jupiter is the second brightest of this trio of planets and is located to the upper left of Venus.  Saturn is the dimmest of the three and located on a line halfway between the gas giant (Jupiter) and the terrestrial (rocky) Venus.

     The only visible morning planet this month is Mars.  Appearing low in the sky between ESE and SE, the Red Planet will be visible about 30 minutes before sunrise early in the month and an hour before sunrise late in the month.  Our observing challenge for you early risers will be to find the old, waning crescent Moon just above Mars on Dec 2 and just below and to the left of Mars in the early hours of Dec 3.  Mars can also be observed 4.5 degrees north of the bright red star Antares on Dec 27 & 28.  

     Our ‘you really want a challenge?’ viewing challenge will be to find Pluto on Dec 21 as Venus passes just 2 degrees north of our oldest known dwarf planet (the width of your little finger held at arm’s length equals 1 degree).  At mag. +15.1, it will require at least binoculars to see the faint ‘former’ planet (in my world, Pluto still rates as a planet) and the pair should just fit into the field of vision at the same time.

     December’s Lunar Cycle will bring a New Moon on Dec 4, followed by the First Quarter (Dec 10), the Full Moon (Dec 18), and the Last Quarter on Dec 26.  Our first peek at a very young Crescent Moon could take place in the western sky an hour after sunset on Dec 5.  Two hours after sunset on Dec 6, a slightly older young crescent will be visible directly below Venus in the SW.  The Farmer’s Almanac identifies the December Full Moon as the Full Cold Moon as “This is the month when the winter cold fastens its grip and the nights become long and dark.”  Alternate names for the December Moon include the Drift Clearing Moon, Frost Exploding Trees Moon, Hoar Frost Moon, Little Spirit Moon, Long Night Moon, Moon of the Popping Trees, Moon when the Deer Shed Their Antlers, Snow Moon, and the Winter Maker Moon.

     If the weather cooperates (never a sure thing around the Great Lakes in December), the Geminid meteor shower will provide the best viewing in the pre-dawn hours of December 14.  Increased meteor numbers are commonly observed for a couple of days before and after the shower’s predicted peak.  The Geminids are created by the orbit of object 3200 Phaethon which is thought to be a Palladian asteroid.  Most meteor showers are caused by the debris ejected from passing comets.  The 3200 Phaethon object is also called a ‘rock comet’ as it forms a dust tail similar to the tail a comet produces as it nears the Sun.  The ‘rock comet’ develops a tail because it passes much closer to the Sun than any other named asteroid.

     Compiled by Ken Raisanen of WOAS-FM – information provided by Abrams Planetarium Sky Calendar, Michigan State University.  More information and subscription information can be found on  their website at or on Twitter at  Yearly subscriptions cost $12 and can be started anytime.

Top Piece Video:  In honor of the passing of Moody Blues drummer Graeme Edge and the upcoming Geminid meteor shower, her is Gemini Dream