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Posted at 10:12 AM ET, 08/31/2012

Blue moon: one small mistake, giant folklore for the sky

If you call old friends on your smart phone only once in a blue moon, start dialing: Today is your day.

For an event that happens about once every 2.7 years, enjoy the full moon – because it’s a Blue Moon… on a Friday… just in time for happy hour.

Modern folklore defines a blue moon as the second full moon in a given month. Washington’s last full moon fell officially on Aug. 1 at 11:27 p.m. (Aug. 2, 3:27 a.m., Universal Time.)

Related: Blue moon and Sturgeon moon in August 2012

Today’s full moon officially was at 9:58 a.m. here. Remain seated at your desks and don’t bother looking right now, because you can’t see it until this evening.

There are several news reports telling people to look for the moon in the morning. If you believe those reports, you’ll be looking a long time. The full moon is essentially opposite from the sun right now – from our earthly perspective. So while the sun is up today, the full moon is not visible.

Tonight’s moon rises in the eastern heavens at 7:25 p.m., moments before sunset in the western sky at 7:39 p.m.

The next blue moon occurs on July 31, 2015. We get two blue moons in 2018 when they fall within January and March. (Always deprived of days, February 2018 gets no respect and no full moon.)

Before you go hunt down your old college astronomy textbooks, you won’t find the definition of a blue moon. It truly is fun-filled, accidental folklore – thanks to Sky & Telescope magazine.

“This colorful term is actually a calendrical goof that worked its way into the pages of Sky & Telescope back in March 1946, and it spread to the world from there,” says Kelly Beatty, senior contributing editor for Sky & Telescope.

The “Maine rule”: Going back two centuries, the blue moon was defined as the third moon out of four in a given season, according to the Maine Farmers’ Almanacs going back to 1819. (Donald W. Olson, Richard Tresch Fienberg and Roger W. Sinnott, from Sky & Telescope, went searching for the Maine Farmer’s Almanacs to confirm this.)

Normally there are three full moons in any season, each with a name, such as fruit moon, paschal moon or harvest moon. Since sometimes there are 13 moons in a year, the third moon out of four in a season became the blue moon – a placeholder name -- so that the other moons would keep their rightful place in a seasonal order.

Kelly explains that in a 1946 Sky & Telescope magazine article, amateur astronomer James Hugh Pruett (1886–1955) incorrectly assumed how blue moon had been used in the Maine Farmers’ Almanac. Pruett unintentionally mangled the original blue moon definition … and it thus became the second full moon in a given month.

Fast forward to the 1980s, when the newly popular StarDate radio show, with Deborah Byrd, could be heard nationally on public radio stations. There she discussed the second full moon of the month as blue, and popularized information from Pruett’s 1946 Sky & Telescope article. Other media picked up on the story – and an innocuous moon becomes blue and launches into accidental folklore.

Americans seemed to like the idea of a blue moon, so it stuck. And, although it’s originally a mistake, astronomers seem to have fun with it because interest in astronomy blossoms.

NASA video: ScienceCasts: Watch Out For The Blue Moon

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Blue Moon and honoring Neil Armstrong: The Slooh Space Camera will broadcast the lunar event live on Slooh.com, free to the public, Friday, Aug. 31 at 6 p.m.

Viewers may watch live on their PC or IOS/Android mobile device. Bob Berman, Slooh Editor and Duncan Copp, documentary filmmaker , will discuss the Apollo program and the late Neil Armstrong’s moon landing.

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Shaken, not stirred: It is Friday, so why not try a Blue Moon Martini while watching the Blue Moon rising.

Credit: How to make a Blue Moon Martini - Drink recipes from Bartending Bootcamp

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Sources: Sky & Telescope, May 1999, Donald W. Olson, Richard Tresch Fienberg and Roger W. Sinnott; “Once in a Blue Moon,” skyandtelescope.com, Philip Hiscock; Observer’s Handbook 2012, The Royal Astronomical Society of Canada; Astronomical Calendar 2012, Guy Ottewell.

By Blaine Friedlander  |  10:12 AM ET, 08/31/2012

Categories:  Astronomy, Latest, Space

 
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