The sky is blue because of how the light from the sun reflects off of our atmosphere. White light (like that from our sun) is actually comprised of all of the colors of the rainbow. When the sun's light hits the particles of our atmosphere, it is scattered into its different colors. Because blue light is of a shorter wavelength, it "scatters" more than the other colors. The different wavelengths of light can be visualized here:
Click the waves to pause.
