Explain how twinkling of stars is an effect of atmospheric conditions on refraction of light.

Explanation

i. Stars are point sources of light as they are very far away from us.
ii. The apparent position of star is slightly higher than its actual position due to refraction of starlight from the atmosphere. The starlight travels from rarer medium to denser medium and continuously bends towards the normal.

iii. Due to the motion of atmospheric air and change in density and temperature, the atmosphere is not steady. As a result, refractive index of air in given region changes continuously and randomly.
iv. Hence, the apparent position of star and its brightness is not stationary but changes slightly.
v. In this way, due to change in refractive index of atmosphere, the stars appear twinkling at night.