With the help of a labelled diagram, explain why the sun appears reddish at the sun-rise and the sun-set.
At sunrise and sunset, the Sun is near the horizon and its rays cover a larger part of the atmosphere. As the intensity of the scattered light is inversely proportional to the wavelength of the colour, therefore, most of the blue light and other components of shorter wavelength are scattered away by the particles. The wavelength of the red colour is the longest among all the components of white light; therefore, it is least scattered and appears to come from the sun. Hence, the Sun looks red at the time of sunrise and sunset.