Question

why planets do not twinkle?

Answer 1

because planet are not luminous so they do not send light toward earth so that it cant be refracted by atmosphere

Answer 2

Planets when seen from Earth's surface don't twinkle. The reason is the planets are much closer to the Earth and are thus seen as extended sources of light.

Consider this.Take a torchlight and flash it on your palm by keeping it at a long distance from your palm..........You will see a clear small dot of light on your palm...Now bring the torchlight closer to your palm, you will see that the light gets blurred and appears bigger.

Same is the case for the planets and the stars. If we consider a planet as a collection of a large number of point-sized sources of light, the total variation in the amount of light entering our eye from individual point-sized sources will average out to zero, thereby nullifying the twinkling effect..