Why is the sky blue?

Eeek! An article specific to color but a yellow Sun is the graphic color choice?

Heliochromology encourages more appropriate use of crayons, especially in grade school where the root of the color conundrum begins. ;)

There is an excellent book, "Why the Sky is Blue" (Gotz Hoeppe) that addresses this along with some very interesting history.

This article was meant to be short, so I'll add a little for those who might be interested:

The blue sky abounds also because of the size (no. of particles) in our atmosphere. If a planet has a more massive atmosphere then more scattering will occur. This would cause more blue light to scattering away from the surface, thus, given enough atmosphere, the net effect would cause the atmosphere to appear as the color of the host star.

Our atmosphere allows for an average scattering number of under 2, IIRC. This, surprisingly, helped Lord Rayleigh calculate what we call Avogadro's number.

The article mentions that our eyes are more sensitive to blue, but are greatest sensitivity is more in the green. Remarkably, only 2% of our eye's color cones are the "blue" color cones. So there are some amplifying effects that take place to bump our blue perception.
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