Wx Savvy | Science

Why Is The Sky Blue?

Our sky appears blue because of our atmosphere. The size of the particles that make up our atmopshere (mostly nitrogen and oxygen) are perfect for scattering blue, indigo and violet. Scattering occurs when the gas molecules that comprise our atmosphere, absorb the bluish colors of sun light and then radiate that bluish color in every direction. In the meantime, the red, orange and yellow colors that are also part of sunlight pass through our atmosphere without being scattered. Here's why:

It all starts with a really smart dead guy named Tyndall.

John Tyndall showed that small, but non-dissolved, particles in a solution will scatter light. This is kind of like how at a movie theater you can see the light from the movie projector streaming towards the screen. The light gets scattered in all directions from small dust particles in the air. This "Tyndall effect" can apply to our atmosphere.

Some other really smart dead guy named Lord Rayleigh, took the Tyndall Effect one step further.

Lord Rayliegh showed how different wavelengths of light (which is the same thing as saying different colors of light) will scatter or not scatter depending upon the size of the substance they are encountering. It just so happens our atmosphere is good at scattering blue, indigo and violet. Red, Orange and Yellow are not being scattered. This is now called Rayleigh Scattering and explains why the sky is blue.

Note To Self:
Become Smart, discover something, then have it named after me, "Steve Scattering? Stevism? The Steve Effect?".

But I digress,

Some Moms out there know that their kids have selective hearing. You hear what you want to hear and block everything else out. So in this sentence, "Clean up your room, walk the dog, take out the garbage and we're getting Pizza for dinner tonight"...I might only hear the words, "Pizza for dinner tonight". That's because I magically ignored everything else. Well, our atmosphere is similar, it selectively scatters only the bluish colors coming from the sun.

Part of seeing colors also has to do with our eyes, which favor blue over indigo and violet. This is one reason why the blue is dominant in the sky (1).

(1) http://math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html