2012/08/31
Once in a blue moon - The blue moon
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Once in a blue moon - Tonight's blue moon
Tonight a so-called "blue moon" set to rise in the night sky, so what is a blue moon, exactly?
A blue moon tale - Somewhat interesting, the answer has nothing to do with the moon's color. The "blue moon" tale is a convoluted one, with much of the action taking place in the relatively recent past....
In 1946,
"Sky and Telescope" magazine traced the term to the "Maine Farmer's Almanac," where it apparently referred to the third full moon in a season that contains four full moons instead of the usual three. The year is divided into four equal seasons, each 91 or 92 days long. Because there are 29.5 days between full moons, four full moons occasionally get squeezed into a single season. [Once-in-a-Blue-Moon Not Really Blue (Infographic)]
But the author of the "Sky and Telescope" article misintrepeted this complicated definition, declaring that a "blue moon" is actually the second full moon in a month with two full moons.
Then, in 1981,
the designers of the board game Trivial Pursuit came across the 1946 magazine article. They put the definition into the game, and suddenly this incorrect explanation of an unscientific term became “general knowledge.”
The blue moon in AugustSo that is why tonight's full moon is known as a "blue moon." It really is no different than any other full moon, except that an accident of the calendar causes it to be the second full moon in the month of August, the first having been on Aug. 1.
While the phrase "once in a blue moon" implies that the skywatching phenomenon should be exceedingly rare, that's not the case. On average, blue moons come along once every 2.7 years.
(Information and photo extracted from http://www.space.com/15455-blue-moon.html)
