Why the sky is BLUE?

 

During the day, Rayleigh scattering, a phenomenon, gives the sky its blue appearance. Sunlight strikes air molecules like oxygen and nitrogen when it enters the atmosphere of the planet. Blue light, which has shorter wavelengths than other colors, is scattered more than other colors by these gas molecules in all directions.  This causes the blue light to be more widely dispersed and visible from all angles, giving the appearance that the sky is blue. As the sun is lower in the sky at sunrise and sunset, more of the Earth's atmosphere must be traversed by the light, which scatters even more of the shorter blue wavelengths and causes the sky to seem more red, orange, or yellow.