Posted by: suekenney | August 31, 2012

Once in a Blue Moon…Is Now

Full Moon

Full Moon (Photo credit: kennytyy)

I’ve heard the phrase “once in a blue moon” all my life.  It was always used to refer to something not very likely to happen.  For instance, “Does that bum down the street ever pay his rent on time?”  “Oh, once in a blue moon!”  Or, “Does my brother ever clean his room?”  “Once in a blue moon!”

 For whatever reason, we never delved into the origin of the phrase, so it wasn’t until I was well into adulthood that I learned that it was used to refer to an actual astronomical phenomenon.  I don’t recall where and when I first heard this, but I learned then that a “blue moon” referred to the second full moon within a month.  Such as today – August 31, 2012, hosts the second full moon of this month, the first one having occurred around August 1 or 2.

I normally don’t keep close track on what the moon is doing, but the nearly full moon I saw last night was hard to ignore, and I had also heard a few mentions of the upcoming phenomena on the radio.  So I thought I’d whip up a quick article on what a blue moon was, and proceeded to do some digging.

Well, well, well.  Look what I found!  “Blue moon” referring to the second full moon within the same month is NOT the original meaning of the term.  Traditionally, according to the Maine Farmer’s Almanac from the 19th century, “blue moon” was the term used for an extra moon within a season.  Usually, each season of the year has three full moons, and many cultures have assigned names to each of those moons – such as the “Egg Moon” of early spring/April or the “Wolf Moon” of midwinter/February or the “Harvest Moon” of early fall/October.  About every two or three years there is an extra full moon within a season; so as not to disrupt the naming sequence already assigned, the third full moon in a season with four is called a “blue moon.”

The switchover in meaning was actually a mistake made in a 1946 Sky & Telescope article, where an amateur astronomer misinterpreted what had been said in the Farmer’s Almanac as referring to the second full moon in one month, rather than an extra moon in a quarter.  Sky & Telescope has since published a correction, but the misinterpretation has stuck in modern folklore.

Another Interpretation:  According to the Wikipedia article I read, the earliest reference in the English language to “blue moon” is from the early 1500’s, when some folks were complaining about their tyrannical clergymen:  “If they say the moon is belewe / We must believe that it is true.”  As we might say it today, “They’re trying to make us believe that black is white, and white is black.”

Yet Another Meaning:   One last meaning of “blue moon” is that you can, on extremely rare occasions, have a moon that actually appears blue!  It can happen after volcanic eruptions or large forest fires:  large particles just slightly wider than the wavelength of red light are put into the air, with no particles of other sizes, so that red and yellow lightwaves are scattered.  After the 1883 eruption of Mount Krakatoa, there were literal blue moons for upwards of two years.

So there’s my take on blue moons.  And this is my 50th post for this blog.  Let’s hope the next 50 come a bit quicker!


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