Question

Explain in brief the reason for the following:

Twinkling of stars

Answer 1

Light coming from the stars undergoes refraction on entering the Earth’s atmosphere. This refraction continues until it reaches the Earth’s surface. This happens because of the temperature variation of atmospheric air. Hence, the atmospheric air has a changing refractive index at various altitudes. In this case, light from the stars continuously travels from a rarer medium to a denser medium. Hence, it continuously bends towards the normal.

The refractive index of the air medium gradually increases with a decrease in altitude. The continuous bending of starlight towards the normal results in a slight rise in the apparent position of the star.

Since the physical conditions of the Earth’s atmosphere keep changing, the apparent position of the star is not stationary. The star changes its position continuously, which makes it twinkle. This happens because light from the stars travels a very large distance before reaching the observer. However, the path varies continuously because of uneven atmospheric conditions. Hence, the stars seem to be fluctuating, sometimes appearing bright and sometimes dull. All this, together, causes the twinkling of stars.