Why the sky is blue?

Question

The sun rises at due East.

What is the ratio of brightnesses of sky in zenith
and near horizon due South immediately after
sunrise?

Answer 1

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.

Answer 2

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.

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Answer 3

The sky is blue because of the greater dispersion of blue light in air. The dispersion goes as the frequency of the light to the fourth power. The blue light disperses so much that we see it coming from every direction, while the red light only comes from the direction of the Sun.

Calculating the answer to your second question would be more difficult than simply going outside and measuring it using a telescope and photometer.

Answer 4

If you want to provide/look up/compute all the cross sections for Raleigh scattering as a function of angle and frequency and the partial pressures/densities of all atmospheric gasses as a function of altitude and the solar irradiance as a function of frequency, then maybe I'll take a crack at answering.

Answer 5

The sky is blue due to an effect known as raleigh scattering where the blue component of white light is scattered more than the red component and therefore more reaches your eye instead of hitting the ground.