Why is the sky blue and not the clouds?

"Why is the sky blue?" This question might look difficult but the reason and physics behind it is not at all difficult. So here is the reason for our sky appearing blue.

There are two things which play an important role in giving color to the sky. First is earth's atmosphere and second is sunlight. So let us know these things first.
The white light coming from the sun is made up of seven colors that are violets, indigo, blue, green, yellow, orange and red. Each of this colored light have a corresponding frequency and wave length associated with it. The violet colored light have the shortest wave length of all and red have the longest.

We know that the earth's atmosphere is formed by different type of gases, water vapor and dust particles. We also know that this component of atmosphere are made up if molecules. So when the sunlight falls on these molecules of the atmosphere it gets scattered. Scattering is a process in which air molecules absorb sunlight and reemit it in various directions. However not all the light is scattered equally. The amount of light that will be scattered is given by Rayleigh law of scattering. This law says that “the intensity of scattered light is inversely proportional to the fourth wavelength of a wave. In simple words if the wavelength increases than the scattering will be less and if the wavelength decreases the scattering will be more. So light of color with smallest wavelength will scatter the more. This includes violet, indigo and blue.  Violet have the shortest wavelength but sky appear blue?
The answer of this is given in the image below

Also check: how named Earth as Earth?

The graph above shows how much of a particular wavelength is emitted by the sun. As you can see in the graph that sun emits more blue and light-bluish light compared to the violet light. Hence more blue light is scattered by the molecules and the sky appears blue. Another reason why we can't see the violet sky is because our eyes are more sensitive to blue color than the violet. So this is how gases scatter light and the sky appears blue.

Now the question comes "do water droplets scatter light?” Well, yes they do but there size is much bigger than the light wave so the scatter all colors of light in equal amount. So the light passing through clouds and dust particles emerges out as white light again. This is the reason why clouds appear white.


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