Why does the sky look blue on a clear day?
Here you go...
Sky looks blue due the scattering of light by the Earth’s atmosphere. Light scattering is a very strong function of the frequency of light. Blue light scatters much more than red light. Because of this scattering the blue light is removed from the solar spectrum which makes the sun appear yellowish and the blue scattered light appears as the beautiful blue sky above you. The scattering by the molecules in the atmosphere is called Rayleigh scattering. This type of light scattering is more effective at short wavelengths- the blue end of the visible spectrum. The scattering function is proportional to the fourth power of the frequency of light. So, blue light will scatter about nine times more than red light.