Full Cold Moon: When Is December's Full Moon and What Is Its Meaning?

A full cold moon as seen from Cornwall, England, on December 13, 2016. In the Northern Hemisphere, the full moon that appears in December is usually referred to by the phrase “full cold moon." Matt Cardy/Getty Images

For those of us in the Northern Hemisphere, the full moon that appears in December is usually referred to by the phrase "full cold moon."

This year it will peak at 12:49 p.m. ET (8:49 a.m. PT) on December 22. The moon will appear very round and full in the night sky near the constellation Orion for two to three days between December 20 and 22, according to EarthSky.

Read more: Super blood moon is coming—total solar eclipse and supermoon converging explained

This year, the full cold moon falls less than a day after the December solstice—an astronomical phenomenon that marks the shortest day of the year in the Northern Hemisphere and the beginning of winter (in astronomical terms). The last time these two events occurred within a day of each other was 2010, and it won't happen again until 2029.

The moon is considered "full" when it is positioned exactly opposite to the sun, or 180 degrees away, with Earth aligned directly between the two bodies.

This alignment only technically occurs at one precise moment every lunar month—the period in which the moon completes a full phase. The term, however, is usually used to refer to the night on the date in which the full moon occurs. In full moon situations, the entire face is illuminated by sunlight, making it appear particularly bright.

The tradition of naming full moons goes back to ancient times when people used to track the changing seasons using the lunar month, rather than the movements of Earth around the sun—the basis for the Gregorian calendar, which is the most widely used calendar today.

For example, historical records show that Native Americans had several names for the various full moons throughout the year, which related to the seasons in some way, according to NASA's full moon blog.

The Algonquin tribes, which were found across the north and east of the North American continent, called the full cold moon the "Long Nights Moon," for example. Meanwhile, ancient Germanic people of northern Europe referred to it as the "Moon before Yule," in reference to a festival that began on the winter solstice.

In most years, there are 12 full moons, or one every month. But in some years, 13 will appear. This means that one month will witness two full moons, with the second usually referred to as a "blue moon."