EXPLAIN : TWINKLING OF STARS

ANS:




The density of the atmosphere is not uniform everywhere as the atmosphere consists of layers of different densities.


The layer at the lower altitude (near earth's surface) is colder and denser than the layer at higher altitude.


Due to this , the refractive index of atmosphere decreases continuously as we move up from the surface.


The star light keeps on bending towards the normal at every point of the atmosphere till it reaches our eyes.


Thus, as shown in the figure(refer to the figure given in the answer for TOTAL INTERNAL REFLECTION) the position of the star appears different from its actual position.


Moreover, the atmosphere is not stationary, i.e. the physical condition of the refractive medium keeps on changing every moment.


This results in continuous shifting of the apparent position of the star as well as variation in the intensity of its light.


This leads to TWINKLING OF STARS.


Unlike stars the planets do not twinkle because they are far closer than stars. Therefore, we can consider stars as point-sized source of light and planets as a collection of large number of point-sized sources (extended objects) of light such that they nullify twinkling effect.