Question

Explain briefly why the sky is blue.

Answer 1

To understand this, we should know the phenomena of scattering. Scattering occurs whenever a polychromatic light strikes an object, some parts of the light is absorbed by the object and the rest is reflected by the object. The reflected light is the colour of the object. Same happens in the case of the sky.

Step by step answer:
We all know about scattering. Scattering is the phenomena by which a ray of polychromatic light strikes a particle of size smaller than its wavelength, it gets re-emitted or redirected in different directions. This is a very common phenomena and is responsible for colour of most of the objects.

Our atmosphere, also called the sky, consists of many small particles like dust, water vapour, etc. the size of some of these particles are less than the wavelength of visible light. Whenever the visible light coming from the sun falls on these particles scattering occurs. The particles scatter light of less wavelength more effectively than light of larger wavelength. The visible light coming from the sun is white light. White light is made up of different colours of light with wavelength in the range of $350nm - 700nm$ . The blue light has a shorter wavelength as compared to red light. So it gets scattered more effectively and comes in our line of sight. This makes the sky look blue.

The diagram shows scattering of white light by atmospheric particles.

Note: While answering any question related to scattering, we should be careful about the wavelength of the light and the size of the particle. Scattering will occur only when the size of the particle is less than the wavelength of the light. Scattering is a very common phenomena and occurs for every particle.