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There’s A “Blue Moon” Tonight And It Won’t Happen Again For 3 Years

For everyone who has ever said you might do something "once in a blue moon," tonight is your night!

Posted on July 31, 2015, at 2:47 p.m. ET

Today brings us the second full moon in a single month.

Dylan O’Donnell / Via deography.com

According to modern folklore, such an event is called a "blue moon."

According to NASA, an early definition of a “blue moon,” from the 1940s, was considerably more complicated and involved “factors such as ecclesiastical dates of Easter and Lent, tropical years, and the timing of seasons according to the dynamical mean sun.”An author named James Hugh Pruett attempted to explain this complex definition (from a Maine Farmer's Almanac) to the readers of the Sky & Telescope magazine in 1946, offering his interpretation that a blue moon was simply the second full moon in a single month. He was wrong, but the definition stuck.
NASA / Via science.nasa.gov

According to NASA, an early definition of a “blue moon,” from the 1940s, was considerably more complicated and involved “factors such as ecclesiastical dates of Easter and Lent, tropical years, and the timing of seasons according to the dynamical mean sun.”

An author named James Hugh Pruett attempted to explain this complex definition (from a Maine Farmer's Almanac) to the readers of the Sky & Telescope magazine in 1946, offering his interpretation that a blue moon was simply the second full moon in a single month. He was wrong, but the definition stuck.

The moon will not actually be blue, but two full moons in a single month is still a pretty rare event.

The last time it happened was in September 2012. The next one won't be until January 2018.
lineartestpilot / Thinkstock

The last time it happened was in September 2012. The next one won't be until January 2018.

Here's a great NASA video explaining the history of the blue moon.

View this video on YouTube

youtube.com / Via youtube.com

So make this blue moon count! Remember: You only blue moon once (in a while).

Kevin Winter / Getty Images
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