Blue sky, something which we see every day, isn’t it? When it is not a cloudy day, then the sky appears blue. If it is clear sky immediately after rain then the color is stronger. Something which we are observing daily. It may be the case that we just notice difference in brightness of this blue color, but we do not go and dig deep to find out reason behind it. Let us try to find it out.
Again it is physics which is going to answer our question. There are a couple of physics principles which explain this. Rayleigh’s principle and Tyndall Effect justify the color. Here is the core of these principles. Blue color is result of scattering of light due to atmospheric gases. As the percentage of Nitrogen and Oxygen is more in atmosphere, you can attribute this effect to these to gases happily. These gases scatter shorter wavelength light more. Violet and blue are the light wavelengths getting more scattered. Our eyes differentiate these colors less, hence finally it boils down to blue only.
Next is why it appears more blue when the sky has cleared just now after rain? Here the dust and water molecules come in picture. After rain, there are less number of dust particles and so the water molecules to do the second scattering in our eye line. When there are more particles and molecules, then the blue light scattered by gases gets scattered again by these elements. It results in hazy blue color. Generally, the sky is less blue on horizon, this is because of same reason, that the dust and water particles are more in our eye line there.
