2 Answers

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This particular phenomenon is due to the dispersion of light.

Dispersion of light is the phenomenon of bending of light as it travels from one medium to another medium. As white light consists of seven different colors .i.e abbreviated as VIBGYOR [ Violet, Indigo, Blue, Green, Yellow, Orange and Red], when it passes through the glass prism, the phenomenon of dispersion of light occurs.

Here, the light signifies the colors.

According to the Cauchy formula, the one with largest wavelength deviates less and one with smallest wavelength deviates more.

So, we see the red light in the top with less deviation and the violet on the bottom with most deviation.

Talking about your problem, why is sky blue? It is so because the most of light scattered in the sky is blue. That's why we see the sky blue.

Hope this will solve your eager.

Note: This phenomenon also explains why we see the rainbow during the rainy day opposite to the direction of Sun.