Explain why stars twinkle while planets do not.

(N/A) The twinkling of a star is due to atmospheric refraction of starlight. As starlight enters the Earth's atmosphere,it undergoes continuous refraction before reaching the observer. This refraction occurs in a medium with a gradually changing refractive index. Because the atmosphere bends starlight towards the normal,the apparent position of the star is slightly different from its actual position. When viewed near the horizon,the star appears slightly higher than its actual position.
Furthermore,this apparent position is not stationary but keeps changing slightly because the physical conditions of the Earth's atmosphere are dynamic. Since stars are extremely distant,they act as point-sized sources of light. As the path of light rays from the star varies slightly,the apparent position fluctuates,and the amount of starlight entering the eye flickers. This causes the star to appear brighter at one moment and fainter at another,which is the twinkling effect.
Planets are much closer to the Earth and are seen as extended sources of light. If we consider a planet as a collection of a large number of point-sized sources,the total variation in the amount of light entering our eye from all these individual sources averages out to zero,thereby nullifying the twinkling effect.