Christmas Full Moon and the Metonic Cycle

Moon December 18 2015

Moon December 18 2015, photo by Dave in Michigan

EarthSky notes that the December full moon will be the first on Christmas since 1977:

This month, the December full moon falls on Friday, December 25, 2015. For Earth’s Western Hemisphere, it’s the first full moon on Christmas Day since 1977.We won’t have another full moon on a Christmas Day until 2034.

A 19-year cycle of the moon is the reason. Amazingly, the moon’s phases recur on (or near) the same calendar dates every 19 years. This cycle – known as the Metonic cycle – happens because 235 returns to full moon almost exactly equal 19 years. So, in other words, the phases of the moon realign (or nearly realign) with the same calendar dates every 19 years. We just missed a full moon on Christmas 19 years ago; instead, the full moon fell on Christmas Eve. It was December 24, 1996 at 20:41 Universal Time, or UT.

…In any year, the phases of the moon take place about 11 days earlier than in the previous year. For instance, the December 2016 full moon will happen on December 14, 2016, and the December 2017 full moon will fall on December 3, 2017.

View Dave’s photo big as the moon and see more in his moon & moon shots slideshow.

More about December’s full moon in Christmas Moon, Snow Moon, Cold Moon, Oak Moon, December Moon on Michigan in Pictures!

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