Twinkling of Stars

example

Effects of atmospheric refraction

Some effects of atmospheric refraction are:
  • Twinkling of stars.
  • Red coloured sun during sunrise and sunset.
  • Blue coloured sky and water bodies.
  • Formation of mirage.

definition

Twinkling of Stars

In reality stars do not twinkle but it appears to twinkle when seen from the surface of the Earth.
Twinkling of stars take place due to atmospheric refraction. In simple terms, twinkling of stars is caused by the passing of light through different layers. These layers have different densities and temperatures. Due to this, light rays bent (refracted) many times in random direction.
As a result stars appear to twinkle. 

diagram

atmospheric refraction

When the light rays pass through the atmosphere having layers of different densities and refractive indices, then refraction of light takes place. This refraction of light by the earth's atmosphere is called "atmospheric refraction".

E.g. At sunrise and sunset the light coming from the sun has to travel a longer distance through the atmosphere to reach us. Therefore the blue and green components of white light are gets scattered away (removed) almost completely leaving the longer wavelength. Hence, during sunrise and sunset the sun appears reddish.