The reason for the red color of sun at sunrise or sunset is __________.

CONCEPT:

Rayleigh's law of scattering:

• According to Rayleigh's law of scattering, the intensity of light of wavelength λ present in the scattered light is inversely proportional to the fourth power of λ, provided the size of the scattering particles is much smaller than λ. Mathematically,

• Thus the scattered intensity is maximum for shorter wavelength.

EXPLANATION:

• The sun looks reddish at the time of sunrise and sunset:

• At the time of sunrise and sunset, the sun is near the horizon. The rays from the sun have to travel a larger part of the atmosphere.
•  As the wavelength of red colour is more than that of blue colour (λ_b≪< λ_r) and the intensity of scattered light is  , therefore, most of the blue light is scattered away.
• Only a red colour, which is least scattered enters our eyes and appears to come from the sun. Hence the sun looks red, both at the time of sunrise and sunset.
• The red color of the sun at sunset and sunrise is due to the scattering of sunlight. Therefore option 2 is correct.