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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