Ask the Professor 2

In a job lot of what I thought was interesting office ephemera I bought at an antiques auction, I found an archive of unpublished correspondence, obviously intended for magazine or journal publication that never came about. I present the second of these here without comment.

Dear Professor,

What is the scientific basis of rainbows?

Sunny

Dear Sunny,

They say that a little learning is a dangerous thing, and in your case it’s the equivalent of holding a backpack nuke in your hand and detonating it to see how tough you are.  Sometimes, I wonder why I bother. 

Still, the call of Science is strong.  She’s like a lover who won’t drive you crazy, a long, cool woman in a black dress, an itsy bitsy teeny weeny yellow polka dot bikini.  And I’m helpless to resist her.

Rainbows?  Simple.  No, more than simple, it’s very simple.  It’s no coincidence that rainbows occur after or during rain.  (There is actually a rare phenonomenon known as the Anticipatory Rainbow, which occurs just before rain.  And then there’s the phenomenon of the recurring rainbow, where the observer thinks he/she has seen the celestial arc before.  This is known as the Deja Bow.)  Rain generally consists of water falling from above in a downwards (vertically) fashion, something which is apparent to even the driest observer.  But what isn’t known is that the due to the velocity of the rain drops’ descent the drops are actually distorted into a crescent shape.  The commingling of millions of crescent shapes results in the classic rainbow shape.

But I can already hear my acute – and picky – detractors saying “Aha!”, which only goes to prove what impoverished vocabularies they have.  “Aha!” they cry again, “but if that were the case, why don’t we have rings in the sky after and during rain, or veritable donuts floating in the heavens?”

Elementary.  The ends of the forming rainbows actually possess the same electrical charge, which keeps them well away from each other, like a a teenager and brussels sprouts.  Soon the classic curved shape results.

The colours?  An optical illusion.  Go figure.