Why is the sky blue?
When light from the sun comes in contact with the molecules of our Atmosphere it scatters in colors of shortest wavelengths, blue and violet. Our eyes are more sensitive to see blue that's why we see the blue sky.
As the light waves enter the atmosphere the waves are bent (refracted ) by the higher density of the atmosphere.
Blue light waves have the shortest wave length so they are refracted the most. Red light waves have the longest wave length and penetrate further into the atmosphere.
What is left to observe is the higher energy short wavelength blue light in the the sky.
Refraction can be observed by placing a pencil in a glass of water at an angle. The pencil will appear to be bent as it "enters" the water.
The reason the sky is blue is the greater refraction of blue light waves.