Above: Angela Demetriou McClain of Botetourt County, Virginia, wrote: “Full Cold Moon, taken at 12:12 a.m. from my front yard … the moment the moon became full.”
The last full moon of 2019 – and the last full moon of the decade – happens on December 11 and 12, 2019. It’s more full on the night of December 11 for the Americas, but, for everywhere worldwide, it’ll look round and full in the sky on December 12, too. Like every full moon, December’s full moon has its own special characteristics. At northerly latitudes, we call it the Cold Moon or Long Night Moon … it’s like a wonderful nocturnal sun, giving us a much appreciated reprieve in the season of diminished daylight.
The moon reaches the crest of its full phase on December 12, 2019, at 05:12 UTC (translate UTC to your time). At the Eastern Time Zone in the United states, that translates to 12:12 a.m. on December 12. Yet, for the rest of the U.S., full moon falls on December 11, 2019 – at 11:12 p.m. CST, 10:12 p.m. MST, 9:12 p.m. PST, 8:12 p.m. Alaskan Time and 7:12 p.m. Hawaiian Time.
Keep reading to learn more about this month’s full moon.
Far-southern December sun means far-northern December full moon
In December, from around the world, the sun rises and sets farthest south of due east and west for the year. For the Northern Hemisphere, these far-southern sunrises and sunsets bring short days and long nights; and in the Southern Hemisphere, these far-southern sunrises and sunsets accompany long days and short nights.
North of the Arctic Circle, the sun neither rises nor sets, because the far-southern sun stays below the horizon at these far northern latitudes. However, since the full moon lies opposite the sun, the December full moon mimics the position of the far-northern June sun. So, north of the Arctic Circle, this December full moon playacts as the June midnight sun.
South of the Antarctic Circle, the far-southern December sun neither rises nor sets, as well, except that the sun stays above the horizon for 24 hours around the clock. But, then, at these far-southern latitudes, the December full moon stays beneath the horizon, like the sun in June.
Yes, the full moon assumes the sun’s position for six months hence. This December full moon shines in front of the constellation Taurus the Bull, or where you’ll find the sun six months later. Despite the short days and long nights of December that must be endured at our northerly latitudes, the December full moon reminds us that the long days of June will prevail once again.
Although it’s somewhat arbitrary, some people might regard the full moon on December 30, 2020, as the last full moon in the second decade of the 21st century (2001 to 2100).
First decade of the 21st century (2001 to 2010)
Second decade of the 21st century (2011 to 2020)
Here’s what Wikipedia has to say about decades:
An ordinal decade in the Anno Domini year numbering system is a period from a year which ends on the digit 1 to the following year which is a multiple of ten; for example, the period from 1961 to 1970 was the 7th decade of the 20th century (or the 197th decade), and the period from 2001 to 2010 was the 1st decade of the 21st century (or the 201st decade).
Also from Wikipedia:
There is currently an ongoing argument whether the ‘new decade’ will begin on January 1, 2020, or January 1, 2021. According to the widely-used Gregorian calender, the 203rd decade will begin on January 1, 2021, as the first year was the year 1, not zero.
A penultimate note … astronomers regard the moon as being full at the instant that it is 180 degrees opposite the sun in ecliptic longitude. At the instant of full moon, the elongation between the moon and sun equals 180 degrees. Visit Unitarium.com to know the present moon-sun elongation, remembering that a positive number means a waxing moon moon and a negative number a waning moon.
A final note … The Geminid meteor shower – one of the highlights of the year for stargazers – will peak around the mornings of December 13 and 14. The moon will be just past full then, and it’ll be lighting up the sky during the peak hours for meteor-watching (around 2 a.m. no matter where you are on the globe). The Geminids tend to be bright, though! So we can expect some meteors to overcome the moonlit glare.
Bottom line: The December 2019 full moon comes only a few days before the expected peak night of the Geminid meteor shower. But the meteors tend to be bright; some may overcome the moonlit glare. Read more about the Geminids. We in North America often call the December full moon the Cold Moon or Long Night Moon.
Bruce McClure has served as lead writer for EarthSky's popular Tonight pages since 2004. He's a sundial aficionado, whose love for the heavens has taken him to Lake Titicaca in Bolivia and sailing in the North Atlantic, where he earned his celestial navigation certificate through the School of Ocean Sailing and Navigation. He also writes and hosts public astronomy programs and planetarium programs in and around his home in upstate New York.