Why is the Sky Blue ?

Why is the sky blue? This is a very common question that comes in mind very often. As we know light consists of seven colors having different wavelengths. These seven colors are: Violet, Indigo, Blue, Green, Yellow, Orange and Red. Amongst these seven colors of light, red has the longest wavelength and violet has the shortest wavelength.

During daytime, light from sun travels through atmosphere and reaches the surface of earth. While its journey to the surface of the earth, it encounters the molecules of air, water vapor, dust particles and many other suspended particles. As it strikes any of these particles the components of light containing higher wavelengths like red and orange passes through them directly without any deviation while the components of light comprising of shorter wavelengths like blue and violet  gets scattered. Thus, the scattering of blue light makes the sky appear blue.

However during sunset and sunrise the sky looks red. This is due to the fact that the sunlight has to travel relatively a longer distance during sunrise and sunset to reach the surface of earth. The blue light mostly scatters away in the upper layers of the atmosphere and the red and orange light get scattered near lower layers of the atmosphere near the surface of the earth.