Refraction At The Time Of Sun Rise And Sun Set

Refraction At The Time Of Sun Rise And Sun Set :

Sun becomes visible about two minutes before the actual sun rise and remains visible for two minutes even after  sun set. Thus duration of the day is approximately increased by 4 minutes.

          
          

As the sun rays enter the atmosphere of earth, they travel from rarer to denser medium i.e., from vacuum to air (µ ≈ 1.003) and density of air go on increasing towards the surface of earth, hence rays of light when enter earth's atmosphere go on bending (Refracting) towards the normal and finally meet at a point i.e., observer on earth.

                          When these refracted rays are produced backward from observer, then it appears that as if they are coming from sun at a position above the horizon, both at the time of sun rise as well as sun set.

                          That is why sun rises 2 minutes early and sets 2 minute late. Also the surface of sun appears flattened at the time of sun rise and sun set due to refraction of light through atmosphere.

Courtesy:.radicesolutions.
                 R.A.Banwat.