00:41 This Won't Happen Again for Years Get ready for a once-in-a-blue moon event. A real Blue Moon, and as Matt Sampson explains, it wont happen again for quite a while.

It's almost time for another blue moon, but we're not talking about a drink. In most cases, the term describes the phenomenon that takes place when there are two full moons in the same calendar month. According to Earth Sky, the next blue moon will occur on July 31 .

Generally, the moon is only full about once every 30 days. This means the blue moon phenomenon can only take place if there is a full moon in the first few days of a month. The last full moon was on July 2.

The phenomenon occurs once every two or three years. The last one took place on Aug. 31, 2012. After this month, there won't be another Blue Moon until 2018 , according to the Orlando Sentinel.

(MORE: NASA Releases Mesmerizing Video of the Moon's Phases )

The Other Blue Moon

The term blue moon has been a point of contingency for many years and has developed quite a few definitions throughout time. Earth Sky claims that the Maine Farmer’s Almanac defines the blue moon as the third full moon out of four in a season. If there are usually three full moons in summer, spring, winter or fall season, then a blue moon would describe the third moon in a rare month that had four.

The concept of a seasonal Blue Moon may have been around longer than the modern definition, but the fight continues as to which definition is more accurate. Either way, your odds of seeing a moon that is actually blue in color are far less likely. These are entirely unpredictable and are based on conditions in the sky among other factors. NASA points to the year 1883 when Indonesia's Krakatoa erupted and massive ash clouds led to blue colored moons for years to follow.

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