Question

Why does the sky appears blue?

Answer 1

Earth's atmosphere is full of particles, small enough that you can't see them. When the sun rays enter the atmosphere they encounter these particles & molecules. This encounter leads to change in the direction of sun rays known as scattering.
The light is made up of different wavelengths, each wavelength corresponding to a particular color. The scattering of a particular color wavelength depends on size of molecule that it encounters, this process of selective scattering is also known as Rayleigh scattering.
The air is perfect scatterer agent for blue & violet color. That is the reason why we see sky blue.




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When the sun's light reaches the Earth's atmosphere it is scattered, or deflected, by the tiny molecules of gas (mostly nitrogen and oxygen) in the air. Because these molecules are much smaller than the wavelength of visible light, the amount of scattering depends on the wavelength. This effect is called Rayleigh scattering,
Shorter wavelengths (violet and blue) are scattered the most strongly, so more of the blue light is scattered towards our eyes than the other colours. You might wonder why the sky doesn't actually look purple, since violet light is scattered even more strongly than blue. This is because there isn't as much violet in sunlight to start with, and our eyes are much more sensitive to blue.
The blue light that gives the sky its colour, is sufficiently bright to make all the stars that we see at night disappear since the light they emit is much dimmer.