A blue moon is usually used to describe a second full moon in a single solar calendar month, which happens every two to three years (seven times in the Metonic cycle of 19 years).[1] The usage of the term "blue moon" to describe the second full moon in one calendar month results from a misinterpretation of the traditional definition of that term in the March 1946 issue of Sky & Telescope. Before then, the term was used to describe the third full moon in a season with four.[2] Owing to the rarity of a blue moon, the term "blue moon" is used colloquially to mean a rare event, as in the phrase "once in a blue moon".[3][4] The term has nothing to do with the actual color of the moon. A literal "blue moon" (the moon appearing with a tinge of blue) may occur in certain atmospheric conditions, e.g. volcanic eruptions and exceptionally large fires can leave particles in the atmosphere.
Posted on: Wed, 21 Aug 2013 03:25:54 +0000
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