Question

write short note why stars twinkle while planets do not?

Answer 1

Twinkling of celestial bodies such as stars is caused by the scattering of light produced by them in the earth’s atmosphere. The stars are very far from earth that is why they appear as twinkling point sources of light. The light produced by stars undergoes multiple refractions travelling through multiple layers of atmosphere and deviates from its path and so the stars appear to twinkle.
Planets are very close to us (earth) as compared to the stars and so appear much bigger than stars and send more light to us. They do not produce their own light. They reflect the light from the sun. They appear as small discs of light. Each tiny point in this disc can be considered as point sources of light. These different points produce either brighter or dimmer effect in such a way that the average of brighter and dimmer effect is zero. Hence, the twinkling effects of the planets are nullified and they do not twinkle. You can also understand in this way, that if some of the light beams from planets are scattered away, others still get through to us, so planets don 't usually twinkle.
Exceptions:
Sometimes in a very stable atmosphere, the stars do not seem to twinkle, whereas in a very disturbed atmosphere, even a planet may appear to twinkle because of the disturbance in the air through which the light is travelling.