This August will bring a rare blue moon, as two full moons will bookend the first and last days of the month. The somewhat rare occurrence in which a month has two full moons leads the second to be dubbed a "blue moon."
The first full moon will arrive on Aug. 1, the second on Aug. 31. A blue moon happens once every 2.66 years, according to Discovery News. Which means it's not nearly as rare as the term "once in a blue moon" may imply.
The truth is, the whole thing is a giant screw-up. The original meaning of a blue moon was defined by the Maine Farmers' Almanac as when a fourth full moon arrives within in the same season -- not a duplicate full moon within the same month. Its meaning was bastardized somewhere along the way, first in a 1946 issue of Sky & Telescope Magazine, and later a syndicated 1980 radio program, according to Discovery News.
All of which wholly ignores the blue moon's status as a misnomer. It rarely changes color for most people.
The moon does appear blue on the few occasions when volcanic eruptions or forest fires send soot floating high into the atmosphere, which augments the hue of the light reflected off the moon. Which leads to the bizarre reality of the colloquial two-fer we formally call a "blue moon" happening pretty often, while a literal blue moon happens only... well, once in a blue moon.