Why is the sky blue?

Why is the sky blue?

The earth is surrounded by an atmosphere. 

The atmosphere (i.e., air, one of the four elements) is a mixture of gasses, mostly nitrogen and oxygen.

The way the sun’s light travels through the atmosphere makes the sky look blue.

White light is made of several different colours, like you see in a rainbow. Each of these colours travel in a wave, but the wavelength (distance between the tops of each wave) varies. Red light has a long wavelength, while blue light has a much shorter wavelength.

When light from the sun enters our atmosphere, the waves collide with gas molecules. The longer wavelengths, like red and yellow, pass straight through and appear to us as “regular” sunlight.

Shorter wavelengths, like blue, bump into the gas molecules and scatter in different directions. Some of it still makes it through directly, but the rest is reflected back to our eyes from all directions, so the whole sky looks blue.