Question

Explain, why during dusk and dawn, the sun appears red in colour?

Answer 1

HintThis question can be answered with the concept of scattering of light using “Rayleigh criteria”. Just compare the wavelengths of different colours in white light and how it scatters when coming in contact with air particles. And you will get your answer.

 Complete step-by-step solution:The rays of the sun are white in colour and as we know white colour consists of seven different colours, all having different wavelengths.
Rayleigh scattering: According to Rayleigh scattering criteria, the light came in contact with small particle scatters, and scattering is inversely proportional to fourth power of wavelength, i.e. \[{\lambda ^4}\].
So, scattering $\propto \dfrac{1}{{{\lambda ^4}}}$
Now, As We know that white coloured light of sun disperses when come in contact with small air particles in the atmosphere.
The wavelength $(\lambda )$ of white light are in order:
VioletHere, we see that violet is of minimum wavelength and red is of maximum wavelength. This means, maximum scattering will be suffered by the violet colour and minimum scattering will be suffered by red colour. Because of higher scattering of violet and blue colour, the sky appears blue to our eyes, because our eyes are touchier towards blue light than violet.
During the rising or setting time of sun, the sun is at the horizon that is at the maximum distance from the earth.as the blue colour has high scattering power, it losses almost it’s complete intensity before reaching to our eyes, but red colour, because of its minimum scattering power, doesn’t lose its intensity and that’s why during dusk or dawn sky appears red in colour (which is almost combination of yellow orange and red colour).

Note:- This Rayleigh scattering criteria is only applicable for dispersion with respect to small particles. You cannot apply this criteria with larger particles. And always remember the sequence of wavelengths. You can remember it as VIBGYOR, here this indicates violet, indigo, blue, green, yellow, red. And remember scattering is inversely proportional to ${\lambda ^4}$