Thursday, September 24, 2020

Why sky is blue in colour | What is Scattering of light


When the sunlight travels in the Earth's circle, it is scattered by the particles in the atmosphere. Light of shorter wavelengths is far more visible than that of larger wavelengths. The amount of scattering is inversely proportional to the 4th power of wavelength. 
(This is called Raleigh scattering.)

This is why the blue character shows the most prominence in the clear sky because the blue character has a lower wavelength than the red one, and its scattering is more Predominantly. In fact, because of the lower wavelength of the violet character, it is more strongly scattering than the blue character. But our eyes are more sensitive to blue than purple, so sky is blue in colour. 

Large particles present in the atmosphere such as dust and microscopic drops of water exhibit different behavior. Here the relevant amount in this context is the relative wavelength of light, λ, and the scatter (assuming their typical size is a). For a << λ, there is a Rayleigh scattering that is proportional to (1 / λ) ^ 4. 

For a >> λ, that is, a scattering object of large size (for example a drop of rain, a large size dust particle or a snow particle) does not have such scattering; All wavelengths are almost uniformly scattered. That's why clouds that contain a >> λ 

There are tiny water droplets of size, usually appearing white. At sunrise and sunset, the sun's rays have to travel relatively far through the atmosphere. Most of the blue and short-wavelength light is separated from this light by scattering. 

Therefore, the least scattering part of the light that reaches our eyes appears to be red. This is why the Sun and the Full Moon appear red when near the horizon.