Why does light at sunset appear red?

1 Answer

Explanation is given below


The sun light has almost all wavelengths of Electromagnetic spectrum from shortest wavelength X-rays to longest wavelength radio waves. But we can see only visible spectrum ranging from #4000\ \text{to} \ 8000 A^\circ#.

According to Rayleigh's elastic scattering, the degree scattering is inversely proportional to #4#th power of wavelength. In this way, the longest visible wavelength i.e. red light scatters less.

During the sunset or sunrise, the sun is at horizon hence the visible light coming sun has to travel the longest distance through the atmosphere undergoing repeated collisions with gas atoms or molecules. Thus, all other colors (except red color) are scattered to greater extent than red light thus red light is dominant during sunset or sunrise. This makes sun appear red.