- Due to the motion of atmospheric air and change in density and temperature, the atmosphereis not steady. As a result, refractive index of air in given region changes continuously andrandomly.
- Due to this, the position and brightness of the star keep changing continuously and the starappears to be twinkling.
- The rays of light from a planet pass through the atmosphere of the earth. As compared to stars,planets are nearer to earth. So a planet can be considered as a collection of large number of point sources of light.
- If the intensity of light from one point source decreases, it increases from the other source.
- Thus, the average intensity remains the same. Hence, stars twinkle but we do not see the twinkling of planets.
