Planets, unlike stars, do not appear to twinkle even though they are also very far away. Give a scientific re…

Question

Planets, unlike stars, do not appear to twinkle even though they are also very far away. Give a scientific reason for this difference in behaviour.

Accepted Answer

## Model Answer Stars appear as **point-sized sources** of light because they are very far away. Due to atmospheric refraction, the amount of starlight entering the eye fluctuates, causing twinkling. Planets, being much closer, appear as **extended sources** (a collection of many point-sized sources). The variations in light from all these individual points average out to zero, nullifying the twinkling effect. Hence, planets do not twinkle. *Source: Chapter 10, Section 10.5 – Twinkling of Stars* --- ## Explanation - The key contrast is **point source (stars) vs. extended source (planets)** — examiners specifically look for this distinction. - Mention "averaging out to zero" for planets — this phrase from the textbook scores well. - Don't just say "planets are closer" without explaining *why* closeness matters (extended source → averaging effect).

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