Have you ever heard the expression "Three times in a Blue Moon"? Of course you haven't. Nobody has. Nonetheless, as we move into 2010, I've heard or seen three relatively reputable sources define the Blue Moon of New Years Eve, incorrectly! So what the heck is a blue moon? Clearly I'm not talking about the Marcel's #1 Hit in 1961... Just to cut to the chase. First the facts, The full moon rising on New Years Eve 2009 is called a "Blue Moon". The last time a Blue Moon rose on New Years Eve was 1990. The current, common, correct definition of a "blue moon" is a 2nd Full Moon in a month. The more correct definition is when any of the four seasons contain 4 full moons, the 3rd is called a Blue Moon(on average, seasons contain only 3 full moons.) Obviously there is some history here - that's the really interesting part. Here's the evolution according to Sky and Telescope Magazine. At some point in history, talking about