Question

Give reasons for the following:

The stars twinkle but the planets do not twinkle.

Answer 1

1. Although stars twinkle at night but planets do not twinkle.
2. The star is situated very distantly from the earth and behaves approximately as a point-sized source of light.
3. As the path of light rays coming from the star, behaving like a point source, goes on varying slightly due to atmospheric refraction, the amount of light entering the eye flickers, and the star twinkles.
4. The planets are much closer to the earth and thus seen as extended sources.
5. So, a planet may be considered as a collection of a large number of point-sized sources of light.
6. Although the amount of light coming from each point-sized source flickers on account of atmospheric refraction.
7. The total amount of light entering our eye from all the individual point-sized sources of the extended source will practically remain unchanged.
8. Therefore, the planets do not twinkle.