Question

Draw a labeled diagram to show (i) the reddish appearance of the sun at the sunrise or the sunset and (ii) the white appearance of the sun at noon when it is overhead.

Answer 1

(i) The reddish appearance of the sun at sunrise and sunset:

1. During sunrise, light has to travel a longer distance to reach our eyes
2. The scattering of light is inversely proportional to the wavelength of the wave. This phenomenon is called Rayleigh scattering
3. $\frac{I_S}{I_0}=\frac{1}{{\lambda }^4}$ , Here $I_S$ is the intensity of light scattered, $I_0$ is the intensity of light incident, $\lambda$is the wavelength
4. Since blue$(450-500nm)$ has the shortest wavelength it gets scattered and red$(700nm)$ having the longest wavelength gets less scattered
5. The shorter wavelengths of light get scattered and only the longer ones reach our eyes
6. Hence the sun appears red during sunrise

(ii) The white appearance of the sun at noon when it is overhead

1. When the sun is overhead the distance traveled by light is reduced
2. There is very less scattering of blue light
3. All the wavelengths have very less scattering
4. All the wavelengths of different colors combine to form white light.
5. Hence, the sun appears white at noon
6. Given below is a systematic diagram of the sun during sunrise and sunset.

Diagram of the sun at sunset/sunrise and when overhead