Why is the sky blue and not any other color like purple or red?
The sky consists of gases that scatter the light. The gas particles are much smaller than the wavelength of the light, meaning the scattering is Rayleigh Scattering. This occurs in all directions, and works best at short wavelengths. Because the blue and purple wavelengths are the shortest, they are scattered most efficiently. However, the gases in the atmosphere, and especially the oxygen and ozone, absorb the purple wavelengths, and therefore the purple is not observed. The other wavelengths (red, yellow and green) are not scattered enough to reach our eyes. Therefore, we see a blue sky. However, the sunlight itself is directed towards us by Mie Scattering, a different form that is not wavelength dependent, and is caused by particles that are larger than the wavelength of light, but still very small (such as dust). This type of scattering projects forwards, and that causes the sunlight to appear white or yellow to our eyes. Mie scattering is also one of the reasons that the evening s
