Why Is the Sky Blue?

"If you can't explain it to a six year old, you don't understand it yourself."-- Albert Einstein

The sky is blue because of the way light works. Light waves are different lengths, blue being short, and most of the light waves in the sky are short, so the sky is blue. Sometimes it is darker or different shades of blue, and that is because of other things in the air such as dust or water drops from clouds.

Okay, I didn't talk about diffusion of light scattered by molecules of various types of gases, and I did not think of a simple way of explaining light waves. But I think it is simple enough for kids who ask the question, and, though simplistic, I think it is pretty close to correct. This is the way I understand it, but I am no physicist.

Why am I thinking about blue skies? The weather has been nice lately, and the sky is blue in Texas. Mainly, I thought about blue skies when I read that Einstein presented the General Theory of Relativity on this date in 1916.

When my boys were young -- maybe 9 and 11 -- I read the theory to them. There were places I skipped over. The equations and their explanations did not make easy reading, but there was plenty of prose that did. The little red book I read had both the special and general theories and I don't remember one over the other, but I remember a couple of stories.

One was about walking on a moving train, and another about the blue sky. I remember these because James and David were impressed by them. I was impressed by how easy the book was to read (not counting the equations.) I read somewhere once that Einstein said science and math should be written so everyone could understand it. What a great idea. If they all wrote as clearly as he did, more kids would want to go into science and math.

Albert Einstein was awarded the Nobel Prize in Physics in 1921. In 1999 Time magazine named him the "Person of the Century." When you think of genius, who comes to your mind?

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