Question: Why is the sky blue???

Sara Imari Walker answered on 15 Jun 2011:

Hi alex, crunchijelly and rachel!! Drew and Julia are correct!! The scattering process they describe which produces the beautiful color of our sky is called Rayleigh scattering. All atoms absorb light at different wavelengths, and they can re-emitt that light at the same wavelengths as it is absorbed. Our atmosphere is mostly made of Nitrogen which absorbs light strongly in blue wavelengths. Therefore, as light moves through the atmosphere, most of the longer wavelengths like red, orange, and yellow pass straight through. However, much of the shorter wavelength light, like blues and purples, is absorbed by the Nitrogen gas molecules (and other molecules such as oxygen!). The absorbed blue light is then re-emitted in different directions and gets scattered all around the sky. So wherever you look at our sky – blue light reaches you so the sky looks blue. This is also why sunsets look red/orange. When we look at the sky with the sun on the horizon we see light reaching us more along a straight line – so the sky looks reddish! Fun stuff =)