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 there is an extra full moon. The extra moon is called a "blue moon." The term "blue moon" is commonly used to describe the rarity of an event, as in the expression, "once in a blue moon." This year's Blue Moon occurs on New Year's eve, December 31, 2009.
May the coming year bring you health & wealth, love & laughter. ♥