Saturday, December 26, 2015

Rare Full Moon On Christmas This Year

Photo credit: Sher Falls

This month, the December full moon fell on Friday, December 25, 2015. For Earth’s Western Hemisphere, it was 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.

But two Metonic cycles ago – 38 years (or 2 X 19 years) – the full moon fell on Christmas Day. That full moon happened on December 25, 1977 at 12:49 UT.


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