Tonight will display a blue moon, the second full moon in August [image: universetoday.com].

The term blue moon originated long ago and was used to refer to bizarre events, or events that seldom occur (and this usage is still common today). This is only speculation, but the term may have originated after a volcanic eruption (or forest fire): if there is a large quantity of smoke or ash spewed into the upper atmosphere, the moon can seem to have a bluish tint.

In more recent times, the Marine Farmer’s Almanac borrowed the term to indicate the unusual event when there were four full moons in a season instead of the usual three. In 1946, James Hugh Pruett, writing an article in Sky & Telescope, misunderstood the reference to mean the second full moon in a calendar month, and this inaccuracy was duplicated during a syndicated radio program in 1980, thereby solidifying the association in the media and the population-at-large (Philip Hiscock (an expert in folklore from the Memorial University of Newfoundland) and Donald W. Olson (an astronomer from Texas) researched and exposed the history of the term blue moon).

Blue moons occur because the moon orbits the earth at a frequency of 29.5 days, which does not match up with the length of the calendar months, resulting in two full moons occasionally occurring in the same month.

Blue moons occur, on average, every 2.7 years, so they are really not that uncommon, but the next blue moon will not occur until July, 2015.

On an unrelated matter; I’m not sure why, but my beard seems to be growing unusually quickly today: I just shaved a couple of hours ago, and I’m already displaying a five o’clock shadow…

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