What is atmospheric refraction ? Use this phenomenon to explain the following natural events : (i) Twinkling of stars (ii) Advanced sunrise and delayed sunset. Draw diagram to illustrate your answer.

Explanation

The density of the atmosphere goes on decreasing as the distance above the sea level increases. Hence, the refractive index of air also decreases. So, light from the sun or other stars undergo multiple refractions before reaching our eyes. This phenomenon is called as atmospheric refraction.
Variations in refractive index of different regions in the atmosphere due to atmospheric refraction causes the variations in intensity of the star light reaching our eyes. Hencee the stars appear to be twinkling.

Atmospheric refraction causes the light rays coming from the sun to be bent. So, the sun which is actually at a position below the horizon, appears in the position above the horizon to a person on the earth. Thus, the Sun appears to rise early by about 2 minutes and set late by about 2 minutes.