Why sky is blue?

     Well you know, There is gases and particles available in earth's atmosphere. When the sunlight reaches atmosphere of the earth, it scattered in all the direction due to all the available particles and gases available in atmosphere of the earth. All the colors scattered in atmosphere with the different wavelength. Red light have the longest wavelength while blue light have the smallest and shorter wavelength. Because of blue colour have shorter wavelength, our eyes captures blue colour in the sky. 

     Rayleigh law states that, The intensity of a scattered light is inversely proportional to the fourth power of wavelength.
     If one reaches the high altitude, They can see a black sky because of absence of earth's atmosphere(no scattering of any colour takes place).

     Scattering light examples are,
                                                  Blue sky, 
                                                  Sunset & Sunrise, 
                                                  Colour of water in deep sea.
     The colour of the scattered light depends on the size of the scattering particles, very fine particles scatters shorter wavelength while larger particles scatters longer wavelength. 
     At the sunrise, The light rays coming from the sun have to travel a greater distance in earth's atmosphere before reaching our eyes. So, shorter waves scattered out by particles and only longer waves survives and reach our eyes.


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