text: A rare blue moon dominated a clear sky Tuesday night, prompting many to take photos. 
   
   The moon rises over the New York skyline in its full stage under a phenomenon called the blue moon, as seen from West Orange, N.J., on Tuesday. (Photo: By Julio Cortez, AP) Story Highlights The phrase 'Blue Moon' refers to the second blue moon in a month 
   
   The next Blue Moon will not take place until 2015 
   
   The traditional Blue Moon is not really blue, but there have been blue moons 
   
   It's been the motivation for romantic songs and popular phrases, and if you're not doing anything tonight, you should head outside or get yourself to a window so you can see it for yourself. 
   
   The last Blue Moon that we'll see until 2015 is up in the sky until Wednesday morning. It's not really blue. The phrase "blue moon" for many people commonly refers to a rare second full moon in a month, although the U.S. Naval Observatory in Washington, while noting disagreement among the public, describes it as, " ... the third full moon to in an astronomical season in which four full moons fall." This kind of moon appears only once every three years, according to the National Oceanic and Atmospheric Administration. 
   
   On social media, amateur and professional photographers took advantage of the clear night and snapped and shared photos of the pristine moon against a navy sky. The buzz came from news organizations to every day people to folks like actor John Cusack, who retweeted a photo of the Blue Moon. 
   
   People had jokes too, tweeting photos of Belgian White Blue Moon ale and video of 1961's "Blue Moon" by The Marcels. 
   
   The Blue Moon also is known as the Full Sturgeon Moon, Green Corn Moon, Grain Moon orFull Red Moon. Initially, the phrase referred to the third full moon in a month, but an incorrect explanation in a 1943 edition of Sky and Telescope magazine stuck, according to space.com. 
   
   By the way, although tonight's Blue Moon is not actually blue, there have been blue moons in history, according to NOAA. The last one, however, appeared over Edinburgh, Scotland, in 1950 and was due to moon light traveling through a cloud of particles from forest fires in Canada, NOAA says. 
   
   
   
   
   
   
   
   
   
   Read or Share this story: http://usat.ly/169QXvH ||||| A blue moon rising tonight is the first full moon of August, yet it is still considered "blue." (Photo: Reuters) 
   
   A blue moon will illuminate the night sky tonight. Pop quiz: what is a blue moon? If you said "a moon that is blue," you'd be pretty wrong, but also sort of right. If you said "the second full moon in a calendar month," with a self-satisfied grin, you'd be sort of right, but should also probably be taken down a notch. If you said "a pretty decent wheat beer," you'd be technically right, but would be off topic. 
   
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   It turns out that the scientific definition of a blue moon is a bit confusing. So here's the deal. 
   
   Though tonight's full moon is the first of August, it is actually a blue moon. That's because the original definition of a blue moon is the third of four full moons in a season, and that is still the most valid definition of a blue moon. 
   
   A little light math is necessary here. The lunation, or lunar cycle, is 29.53 days; one solar year is 365.25 days. This means there are 12.37 lunar cycles every solar year -- a number slightly larger than cycle of 12 months that makes up our calendar year. That means that 12 calendar months (or one year) are about 11 days longer than 12 lunar cycles. These "extra" 11 days accumulate, so that every two to three years there end up being an additional full moon in a season. 
   
   A new definition of a blue moon emerged in 1946, and all because of a mistake in an astronomy magazine Sky & Telescope. In the article "Once in a Blue Moon," amateur astronomer James Hugh Pruett quoted the 1937 Maine Farmer's Almanac (which is unrelated to the more famous Farmer's Almanac), saying that the moon sometimes "comes full thirteen times in a year." 
   
   "Seven times in 19 years there were -- and still are -- 13 full moons in a year," Pruett extrapolated from that quote. "This gives 11 months with one full moon each and one with two. This second in a month, so I interpret it, was called Blue Moon." 
   
   That's the definition, "two full moons in one calendar month," that has stuck for most people. (It's also a far less complicated definition to understand, so maybe that helped too.) 
   
   Then there is the other literal definition of a blue moon, in which the moon appears to be, well, blue. That can occur when particles in the atmosphere cause the moon to take on a hue. 
   
   For instance, when Krakatoa erupted in 1883, the moon appeared to be blue for almost two years. 
   
   "There was a time, not long ago, when people saw blue moons almost every night. Full moons, half moons, crescent moons--they were all blue, except some nights when they were green," wrote Tony Phillips on NASA's Solar System Exploration site. Large ash particles from Krakatoa "[scatted] red light, while allowing other colors to pass. White moonbeams shining through the clouds emerged blue and sometimes green." 
   
   Similar "blue moons" occurred in 1983 in Chiapas, Mexico, after the eruption of the El Chichon volcano, and in Mount Pinatubo in the Philippines in 1991. 
   
   Now that the confusion is cleared up, go enjoy your blue moon tonight. The next one won't be until July 31, 2015, if you go by the "mistake" definition, or on May 21, 2016, if you go by the original definition. 
   
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target: – Photographers were out in force last night to capture a rare blue moon. No, blue moons aren't actually blue (although there have been moons that were blue, most recently in 1950); rather, the term refers to the second full moon in a month, USA Today reports. But wait, you exclaim! Last night was August's first full moon, so something must be amiss, right? International Science Times clears things up: The first (and, in its telling, "most valid") definition of a blue moon is the third of four full moons that occur in a single season. A season would typically have only three, and this extra moon comes about every two to three years. The next will be in 2015.