A blue moon is a full moon that is not timed to the regular monthly pattern. Most years have twelve full moons which occur approximately monthly, but in addition to those twelve full lunar cycles, each calendar year contains an excess of roughly eleven days. The extra days accumulate, so that every two or three years (on average about every 2.7154 years), there is an extra full moon. The extra moon is called a "blue moon."
They say that there are two different definitions of blue moon...
- The first definition is when a full moon occurs twice in one month. In this case, the second full moon is called a blue moon.... so there will be a blue moon on new years eve!!!
- The second definition of a blue moon is when there are four full moons in one season, the third full moon is considered the blue moon. Hmm, sounds correct —though the other definition has become more widely known.