why is the sky blue?

Question

What chemicals in the atmosphere make the sky appear blue?

Answer 1

I would like to add to answers something for you to think about. Why the sky is not violet? It is true that the shorter the wavelength, the stronger the scattering is. Then the sky shall be violet, since the violet light has shorter wavelength than the blue light. So why not?

Answer 2

I would like to add that it also has to do with the makeup of the Earth's atmosphere.  Earth's atmosphere is made up of mostly nitrogen and the blue light is affected by the gas more than other (ROYG) colors. - Just as the others said.

But, if the atmosphere was made of other elements the color would/could be different.

So I would say the answer to the question you asked is - the nitrogen.

It turns out that one (or more) of the energy transitions of nitrogen is in the blue range.  So this is why when the light passes through the atmosphere nitrogen absorbs and re-emits the blue.

 

There is a sci-fi show <<I wish I could remember which one>> where when the humans arrived the sky looked more violet.  One of the people in the expedition commented on it and the scientist gave a short answer to it.  On this planet the blue light was making it through the atmosphere but the violet light was being scattered due to Rayleigh scattering.

Answer 3

The sky is blue because of Raleigh scattering  of the sunlight  in the Earth atmosphere. This type of scattering (while the other portion of the light reaches the Earth's surface) is described by the function inversely proportional to fourth degree of the light wavelength: ∼λ^-4). Because the wavelength of blue rays is shorter compared with wavelengths of other parts of the visible light, this proportionality means that blue rays are more sensitive to the scattering than other parts of the visible light. This effect makes the sky blue just because in daytime the sunlight travels short distances in the atmosphere.  

Answer 4

Why is the Sky Blue?

The blue color of the sky is due to Rayleigh scattering. blue skyAs 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.

 

obtained from http://www.sciencemadesimple.com/sky_blue.html