Why does the sky sometimes appear white?

  1. Our atmosphere contains atoms and molecules of different sizes.
  2. According to their sizes, they are able to scatter different wavelengths of light.
  3. For example, the size of the water molecule is greater than the size of the $N _{ 2 }$
    or $O _{ 2 }$.
  4. It acts as a scattering centre for light other frequencies which are lower than the frequency of blue light.
  5. In a hot day due to rise in the temperature, water vapour enters into atmosphere which leads to abundant presence of water molecules in atmosphere. These water molecules scatter the colours of other frequencies (other than blue).
  6. All such colours of other frequencies reaches our eye and white colour is appeared to us.