Happy New Year, folks...it's a rare one, sporting a Blue Moon, a term that simply refers to the second full moon in a calendar month, something that hasn't happened on a New Year's Eve for nearly 20 years, NASA says.
"December 1990 ended with a blue moon, and many New Year's Eve parties were themed by the event," said Professor Philip Hiscock of the department of folklore at Memorial University of Newfoundland, in Canada.
Most months have just one full moon, because the 29.5-day cycle of the moon matches up pretty well with the length of calendar months. Occasionally, there will be two full moons in a month, something that happens about every 2½ years, NASA says.
But a blue moon on December 31 is rare.