Question

How does refraction take place in the atmosphere? Why do stars twinkle but not the planets?

NCERT Class X
Science - Exemplar Problems

Chapter_The Human Eye and
the Colourful World

Answer 1

our atmosphere consist of various layers of air . as we go up in the atmosphere these layers gradually become rarer when light comes from a distant stars and   enter in our atmosphere it refracts 1/1 from these layers of increasing refractive index after every fraction the light bend towards the normal and to the observer on earth the stars appear not only that due to strong wind and convection currents refractive index of these layers keep on changing these changes the apparent position of the star and the observer on the earth observes that the stars appear twinkling
on the other planet do not twinkle because
1. they are not source of light but reflect low intensity light of the sun.
2. they are much closer to the earth and subtemd larger angle on the eyes of the observer

Answer 2

In the atmosphere we have air everywhere but all the air in the atmosphere is not at the same temperature some of the air layers of the atmosphere are cold whereas other layers of the atmosphere are comparatively warm now the cooler air layers of the atmosphere behaves as optically denser medium for light rays where as the warmer are layers of the atmosphere behave as optically rarer medium for the light rays same atmosphere we have areas having different optical density and when light rays pass through the atmosphere having a layers of different optical density is then refraction of light takes place the refraction of light caused by the earth atmosphere is called atmospheric refraction