Astronomical optics: Why do planets not twinkle like stars? State the physical reason based on apparent size and atmospheric scintillation effects.

Difficulty: Easy

Planets are self-luminous while stars are not
Planets are much closer and have appreciable apparent disks, so atmospheric fluctuations average out
Planets emit radio waves only
Planets have no atmosphere

Correct Answer: Planets are much closer and have appreciable apparent disks, so atmospheric fluctuations average out

Explanation:

Concept
Twinkling (scintillation) is due to random refraction by atmospheric turbulence. A point-like source fluctuates strongly.

Reason
Planets subtend a finite angle; light from different parts averages through the turbulent cells, so brightness appears steady.

Final Answer
Planets are much closer and have appreciable apparent disks, so atmospheric fluctuations average out

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