Question

Why do stars twinkle but planets do not?

Answer 1

Hint: Refraction of light through the various layers of earth’s atmosphere causes the twinkling.

Complete answer:
Whenever we look at the sky at night, we see the twinkling of the stars. One might definitely have this thought in mind that if stars twinkle why the planets don’t. This can be explained as follows:
Stars are farther than the planets from the Earth’s surface. When viewed from the earth’s surface using a telescope the stars appear like pin-point objects whereas the planets appear as disc objects.
The light coming from the stars appears to be coming from a single point. Further, when the light comes from the stars it undergoes numerous refractions due to the presence of the Earth’s atmosphere and leads to the zig-zag pathway of the star-light. This refraction is responsible for the light becoming brighter and then dimming again. This flickering of the stars is known as twinkling. But in case of the planets, the light undergoes refraction but as they are quite closer, the brightening and dimming does not occur. Thus, the planets shine steadily.

Note:
This twinkling of the stars is technically known as astronomical scintillation. The twinkling occurs due to the Earth’s atmosphere. Both the planets and the stars would have shined steadily if there was no atmosphere.