KnowHOW team explains: White light comprises a mixture of seven different colours. The wavelengths of these seven colours present in the visible spectrum (VIBGYOR) vary from one another. When white light falls on an object, it absorbs light of some colours and reflects or transmits light of the rest of the colours. The colour of the object as perceived by us depends on the wavelength of light reaching our eyes after reflection or transmission.

Snowflakes are agglomerates of several ice crystals. The complex structure of ice crystals results in countless tiny surfaces from which visible light is efficiently reflected. When a beam of light enters the snowflake, it gets scattered by the ice crystals. This scattering causes most of the light rays to bounce out of the snow pile. The seven coloured wavelengths present in the visible spectrum when combined in equal measures forms white light. The observer’s eye receives all the seven coloured wavelengths in equal proportion. Hence snow appears white in colour to the observer.

But snow isn’t always white in colour. Sometimes it can be blue in colour. This happens when the layer of snow is about a metre thick. This happens because ice absorbs little amount of blue-coloured light rays. Thus the blue-coloured light rays are scattered by it. This build up of blue wavelengths imparts a bluish hue to deep snow.

The question was sent by Ayon Tarafdar, Asansol