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A rare "blue moon" is pictured in Los Angeles, the United States, on Jan. 1, 2010. 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 the blue moon occurs every two or three years (7 times in the 19-year Metonic cycle) with the extra days accumulated in solar calendar compared with lunar cycles. (Xinhua photo) |