by Rachel L. Smith
“Once in a blue moon” is an expression you may have heard before. It is now taken to mean “rarely”, deriving from an 1821 writing, Real Life in London by Pierce Egan, where he writes:
“How’s Harry and Ben? – haven’t seen you this blue moon.”
A celestial “blue moon” is now popularly known as the second full moon in a calendar month, and it in fact doesn’t happen that rarely; about once every 2.5 years. This Friday (August 31st) will be one such occurrence. So be sure to look up! The next one won’t be until July 2015.
Will the Moon look blue? Not likely. A blue-colored moon is actually quite rare, and is the result of unusual sky conditions where particles of dust or smoke can make the Moon appear blue. The color we will most likely see will be gorgeous pearly gray (as shown above).
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