- The sky appear blue due to atmospheric refraction and scattering of light through molecules.
- Molecules are called scattering centres.
- The reason to blue sky is due to the molecules $N _{ 2 }$ and $O _{ 2 }$.
- The sizes of these molecules are comparable to the wavelength of blue light.
- In the absence of molecules there will be no scattering of sunlight and the sky will appear dark.
- We should appreciate the molecules which are scattering centres.