What is a Blue Moon?

A blue moon refers to the third full moon in a season with four full moons. The term has also mistakenly been used to refer to the second full moon in a month. Most years have twelve full moons that occur approximately monthly. In addition to those twelve full lunar cycles, each solar calendar year contains roughly eleven days more than the lunar year of 12 lunations. The extra days accumulate, so every two or three years (7 times in the 19-year Metonic cycle), there is an extra full moon.

The next Blue Moon is actually August 21, 2013

But enjoy it anyway and remember US Astronaut Neil Armstrong while you look up at it!


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