Question

Why do the stars twinkle but planets don't?

Answer 1

The twinkling of a the star is due to atmospheric refraction. Distant stars act like a point source of light. As the beam of starlight keeps deviating from its path, the apparent position of star keeps on changing because physical conditions of earth’s atmosphere are not constant. Hence, the amount of light which enters our eyes fluctuates from bright to faint. This is the “Twinkling effect of star”. But planets are much closer to us than stars, so they are not point-sized objects to our eye. Hence, the fluctuations have a negligible effect and they don’t seem to twinkle.