KnowHow Team explains: The sky appears blue to us because of the scattering of sunlight by gases and particles present in the atmosphere.

As light moves through the atmosphere, it continues to in a straight line until it bumps into dust particles or gas molecules. Then what happens to the light depends on its wave length and the size of the thing it hits. Dust particles and water droplets are much larger than the wavelength of visible light. When light hits these particles, it gets reflected in different directions. The different colours of light are all reflected by the particle in the same way. The reflected light appears white because it still contains all of the same colours.

Gas molecules are smaller than the wavelength of visible light. If light bumps into them, it acts differently. When light hits a gas molecule, some of it may get absorbed. After awhile, the molecule radiates the light in a different direction. The colour that is radiated is the same colour that was absorbed. The different colours of light are affected differently. All of the colours can be absorbed. But the higher frequencies (blues) are absorbed more than the lower frequencies (reds). This process is called Rayleigh scattering, after Lord John Rayleigh, an English physicist, who first described it in the 1870’s.

The old school of thought, however, believed that the sky appeared to be blue due to the reflection of light of that colour by the seawater. However, scientists later proved this was wrong.

The question was sent by Sunil Shrivastava, Jamshedpur