Friday, 31 August 2012

How to get the blues without holding your breath


It is not at all unusual to hear the words:  ‘they only come along once in a blue moon’--when you are standing at a bus stop.   Blue moons are not as rare as buses on a rainy day, but then again, they do not happen with monotonous regularity either (15 in the next 20 years?).  But today is one of those days.  If you are standing at a bus stop tonight, the full moon in the sky above you will be a blue moon.

 As a measure of rarity,  ‘a blue moon’ sounds wonderfully exotic.  It is the very stuff of romance: ‘Blue moon/you saw me standing alone/without a dream in my heart/without a love of my own’, as the Rogers and Hart song has it.  For some reason blue moons always make me think more of ‘Pale hands I loved beside the Shalimar’ -- either because Kashmir seems so much more intriguing than say, Gorgie, or maybe because I have some subconscious understanding that the light from a blue moon would be enough to make anyone look like a bucket of skimmed milk?

But of course, blue moons aren’t blue at all.  A blue moon is, rather more pedestrianly, when a full moon is seen twice in the same calendar month--not so rare as Halley’s Comet or hen’s teeth, but intermittent enough to lend interest, happening every two to three years.        This definition has evidently only been around since 1946, so is a comparatively modern usage. In the 19th century you said something wasn’t going to happen ‘until a blue moon’ if you meant it was never going to happen.  At some point this usage was overtaken by flying pigs (which, as far as I know, are not related to cows jumping over the moon, although as a child I was reliably informed that the moon was made of green cheese).

 Another, older and rather more confusing definition of a blue moon is the third of four moons in a single season.  I think I get that... but two full moons in a calendar month is the Trivial Pursuit definition of a blue moon, so that must be right? Right? (this from the woman who once answered the Trivial Pursuit question:  Which airplane is launched with a rubber band?  ‘A B52’, I replied brightly.  For those not up on airplanes, this is a very large, lumbering bomber.  I blame my education...).

However, just because blue moons aren’t blue, that doesn’t mean you are never going to see a blue moon.  According to Spaceweather.com, ‘Volcanoes and wildfires fill the air with ash and dust. If the airborne particles are just the right size--about 1 micron (one millionth of a meter) wide--they act like a color-filter, tinging the moon blue. Clouds of water droplets, ice crystals or fine-grained sand can do the same thing.’

Blue or not, sometimes I would rather just do without the science.

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