Article from the website edition.cnn.com.
(CNN)If anything unusual happens to you Friday, you'll be right to say it was "once in a blue moon."
The July 31 appearance of the month's second full moon will be the first such occurrence in the Americas since August 2012. Every month has a full moon, but because the lunar cycle and the calendar year aren't perfectly synched, about every three years we wind up with two in the same calendar month.
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