why is the sky blue

The atmosphere is the mixture of gas molecules and other materials
surrounding the earth. It is made mostly of the gases nitrogen (78%), and
oxygen (21%). Argon gas and water (in the form of vapor, droplets and ice
crystals) are the next most common things. There are also small amounts of
other gases, plus many small solid particles, like dust, soot and ashes,
pollen, and salt from the oceans. The blue color of the sky is due to
Rayleigh scattering. As light moves through the atmosphere, most of the
longer wavelengths pass straight through. Little of the red, orange and
yellow light is affected by the air. However, much of the shorter
wavelength light is absorbed by the gas molecules. The absorbed blue light
is then radiated in different directions. It gets scattered all around the
sky. Whichever direction you look, some of this scattered blue light
reaches you. Since you see the blue light from everywhere overhead, the sky
looks blue. As you look closer to the horizon, the sky appears much paler
in color. To reach you, the scattered blue light must pass through more
air. Some of it gets scattered away again in other directions. Less blue
light reaches your eyes. The color of the sky near the horizon appears
paler or white.


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