9-1/4 x 10-1/4"
Ink drawing printed over watercolor |
Blue SkyThe blue of the sky and the blue of the distant hills are the visible sign of the action of sunlight on air’s tiniest particles, its molecules of gas. Sunlight can be understood in terms of wavelengths or in terms of small particles of energy, called photons. The photons travel at approximately 186,280 miles per second. According to the frequency of their photons, they vary in kind, and we distinguish the variations by name: red, orange, yellow, green, blue, and purple. Red, for example, is a low frequency light. • • • • • • •
Blue is a high frequency light.
• • • • • • •
Few air molecules are touched by an infrequent red photon, but many are hit by the rapid-fire blue photons, which scatter their color on impact. We can see the photons’ scattering directly overhead against the black of outer space and between ourselves and distant hills.
If we lower our gaze halfway to the horizon, we look through the air layer at an angle so the increase in scattering introduces a hint of lower frequency — lower than blue — which is green. • • • • • • •
As we lower our eyes still further, to just above the horizon where larger particles of dust and pollution are added to the air, the colors combine into all inclusive white.
Purple has a higher frequency than blue. •••••••
But it is almost out of the range of light we can see, so to our eyes the blue overwhelms it.
Some non-human eyes view it differently. Bees see into the ultra-violet, which has an even higher frequency than purple, and is invisible to us. Flowers, whose business it is to attract pollinators, have evolved designs that we only know about from pictures taken with ultraviolet-sensitive film. |