- Scattering of sunlight through molecules of atmosphere is the reason for the blue of the sky.
- Our atmosphere contains atoms and molecules of different sizes.
- According to their sizes they are able to scatter different wavelength of light.
- For example, the size of the water molecule is greater than the size of the $N _{ 2 }$ or
$O _{ 2 }$ - It acts as scattering centre for other frequencies which are lower than the
frequency of blue light. - Blue colour scatters more than other colours.
- That is why sky appears blue.