Question

Atmospheric Refraction . Explain
with eg
1. twinkling of stars
2.Advanced sunrise and delayed sunset

Answer 1

Twinkling effect of stars:-

Starlight on entering the earth’s atmosphere undergoes refraction continuously in different layers of varying densities before it reaches earth. Hence it appears to shimmer as the light passes through varying densities and refractive indices.

Advanced sunrise and delayed sunset

The sunrise is advanced due to atmospheric refraction of sunlight. An observer on the earth sees the sun two minutes before the sun reaches the horizon. A ray of sunlight entering the earth’s atmosphere follows a curved path due to atmospheric refraction before reaching the earth.This happens due to a gradual variation in the refractive index of the atmosphere. For the observer on the earth, the apparent position of the sun is slightly higher than the actual position. Hence, the sun is seen before the sun reaches the horizon.Increased atmospheric refraction of sunlight occurs also at the sunset. In this case, the observer on the earth continues to see the setting sun for two minutes after the sun has dipped below the horizon, thus delaying the sunset.

Answer 2

Twinkling of star is due to the atmospheric refraction of starlight. The atmospheric refraction occur in the medium of light of gradually changes the refractive index

Since the atmosphere bends the star light toward the normal the apparent position of star is slightly different from the actual position these apparent position of star is not stationary but keeps on changing slightly.