Why does the sun seem to rise two minutes before the actual sunrise and set minutes after the actual sunset ? Explain with the help of a labelled diagram.

Explanation

The temperature, density, and hence refractive index in different regions of the earth.s atmosphere change continuously. With increasing altitude, the refractive index of the earth.s atmosphere goes on decreasing due to decreasing density of air. This causes atmospheric refraction which results in the bending of sunlight reaching the earth, towards the normal. So, to an observer on the earth, the sun appears to be slightly above its actual position as shown in the figure. Thus the sun appears to rise early by about two minutes and for the same reason, it appears to set late by about two minutes.