why is the sky blue

• the sky looks blue (most days in california, at least) due to the scattering of sunlight off air molecules in the atmosphere
• this scattering is called Rayleigh scattering & this scattering is more effective at short wavelengths of the visible spectrum of light (colors that are at the end of ROYGBIV)
• so when air molecules bend sunlight off its straight path and down toward the ground, most of that redirected light is blue.

• the blue of the sky is more saturated the farther you look away from the sun. the sky near the sun is a more white color due to mie scattering, which is not wavelength dependent

• bigger particles scatter differently than smaller particules. the blue in the sky comes from Rayleigh scatter that happens from particles much smaller than the wavelength of light (380-750 nano meters). so effectively this is the oxygen and nitrogen in our atmosphere. particles larger than the wavelength of light cause mie scattering, which affects all colors equally, so it makes the sky look whiter or hazier.

  

http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/blusky.html#c2