On a day when the sun and the sky are not obscured by clouds, the sky appears to be a clear bright blue color. Did you ever wonder why? That ponderous question never once crossed my mind until my ten-year old nephew posed it, and when I couldn't answer him, he proceeded to explain it to me. I guess I flunked the test. Naturally, he gave me his ten-year old version. Later I checked to see if he had it right, which surprisingly, he did.
The earth is surrounded by a layer of stuff we call an atmosphere. There's really nothing there you wouldn't expect to find; there's oxygen, and nitrogen, water vapor, water droplets and ice crystals along with dust, soot, ashes, pollen and ocean salt.
So that's the situation with the atmosphere, which you could think of as the canvas which will be painted blue by the light from the sun.
Everyone has heard the term "light wave." That's how light travels; in waves. It proceeds along a perfectly straight line provided it doesn't encounter an object in its path. However, if the light smacks into a tiny speck of dust or a gas molecule, things begin to happen.
The solid particles in the atmosphere are much bigger than light waves. When the light hits them it bounces off in multiple directions. The light still looks white because it rebounds intact; staying the same color it was before colliding with the particle.
The real action happens when the light hits a gas molecule because gas molecules are smaller than light waves. Some of the light gets absorbed by the gas, and later the gas will release it and send it off in a different direction. The red, orange and yellow light mostly passes straight through the gas without being interrupted. But the higher frequency colors, in the blue spectrum, are likely to be absorbed by gas so there is a lot of blue that gets captured in the atmosphere.
In fact, there is so much blue captured by atmospheric gas and released in multiple directions that no matter where you look at the sky on a clear day, you see blue light.
I recommend you keep this information tucked away in the back of your mind because you never know when a ten-year old will look up at you and ask the age-old question; "Why is the sky blue?"
Don Caron is a composer of ballet class music and likes scienc for recreation. You can listen to some of his music at CDBaby. You can also watch his music videos at YouTube Ballet Class Music
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