Why do stars twinkle?

Hint: In this question, we will know why stars twinkle, the main reason behind this if the phenomena ‘refraction’. This will help us to know what happens to the light rays falling from planets to our eyes. Further, we will study why planets do not twinkle, for our better understanding.

Complete answer:
As we know that the twinkling of stars is due to atmospheric refraction of light from the star when it approaches us on the earth.

Our earth’s atmosphere is made of several layers and the refractive indices which keep on changing continuously. Due to this path of light rays or the radiations from the star to us keep on changing their path continuously. This leads to the consequence that the number of rays entering, the pupil of our eye goes on changing with time period and thus the stars appear to us twinkling.

Therefore, we get the required reason for the twinkling of stars.

Additional information:
$\bullet$ Here, we know that planets shine more steadily because they are closer to Earth and so appear not as pinpoints like stars, but they appear as tiny disks in our sky. We can see planets as disks if we look through a telescope, while stars remain pinpoints.
$\bullet$ We know that the light from these little disks is also refracted by Earth’s atmosphere, when it travels toward our eyes. While the light from one edge of the planet’s disk might be forced to ‘zig’ one way and light from the opposite edge of the disk might be ‘zagging’ in an opposite way. So, these zigs and zags of light from a planetary disk cancel out each other, and this is the reason why planets appear to shine steadily, or not twinkle like stars.

Note:
Here we note that refraction is the reason for twinkling of stars. Further, we should know the difference between reflection and refraction i.e., reflection is the change of the direction of wave or light to back to its original medium whereas, in refraction light slightly bends towards the normal when the medium is changed.