Rainbows

A rainbow at Whitney Lake, Alberta

The rainbow is an ethereal artifact; progeny of the sun and rain.  I had an interesting discussion with one of my science classes on them.  The students thought that it was an actual physical thing that could be touched.  It did not occur to them that its vapourous existence was the result of bright sunlight refracting through billions of raindrops.  It seemed inconceivable that this curved pillar of symbolism should be nothing more than the result of bent light rays hitting the retinas of their eyes.

You can create your own rainbow on a sunny day by generating a fine mist of water.  The water drops form into tiny spheres, a product of the cohesive forces of water and surface tension acting in unison.  Light entering these spheres follows the rules of refraction and bends; longer wavelengths like blues bend more than shorter wavelengths like red.  The nature of matter following the laws of physics creates this icon of happiness and joy.

It gets weirder when frozen water vapour is involved.  High up in the atmosphere, much farther away from the Earth than planes even fly, are tiny crystals of water which have sublimed onto miniscule dust particles we call condensation nuclei.  These crystals are not spherical, but rather flat.  They are further orientated parallel to each other to produce the effect; randomized crystals would only serve to scatter the light without incident.  Sunlight filtering through these shards refracts as before and the sundog is produced. 

As I looked up sundogs to verify my musings, I came across something I have never actually seen before.  The term sundog actually refers to the bright points of light occurring at opposing ends of the refractive halo.  I have only ever seen the halo, which I have been apparently mistaking for a sundog.  If you want to see a pair of sundogs, have a look at the youtube video I linked to below.

https://www.youtube.com/watch?v=8GHZOvhxS1E