Posted on Sep 12, 2012 in Science & nature
It’s a basic question, but I still don’t know: Why is the sky blue?
It’s because “Mr Green Sky” wouldn’t have worked for ELO.
Well, even though that’s true, that’s not the reason. As per usual, we turn to science for our answer.
The sun acts as a black-body radiator (the glow of a body with no color of its own), and gives off what we humans perceive as white light — a color temperature of about 5,780 Kelvin, which is actually a bit to the reddish-pink side, but close enough for government work.
Now, this white light, as you may or may not remember from your high school physics, is made up of all the other colors of light mixed together — the principle of additive color. This is, of course, the opposite of mixing inks or pigments together — which theoretically gives you black, but generally results in a dark gray.
Anyway, this combination of light colors we call white light smacks into the earth’s atmosphere, and a funny thing happens — most of the colors that make up the white sunlight pass through the atmosphere without too much incident — except for blue light. It turns out the molecules of nitrogen and oxygen (that make up most of our air) tend to scatter blue light more than any other color. It is this scattering effect — known as Rayleigh scattering — that gives the daytime sky its blue color.
So why, you may ask, does the sun turn the sky red and orange at sunrise/sunset? Pretty simple, actually — during those times of day the blue light is scattered away from our line of sight, creating the beautiful warm tones we see in the early morning and early evening.
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