Astronomical optics: Why do planets not twinkle like stars? State the physical reason based on apparent size and atmospheric scintillation effects.
IIT JEE
Physics
Difficulty: Easy
Choose an option
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APlanets are self-luminous while stars are not
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BPlanets are much closer and have appreciable apparent disks, so atmospheric fluctuations average out
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CPlanets emit radio waves only
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DPlanets have no atmosphere
Answer
Correct Answer: Planets are much closer and have appreciable apparent disks, so atmospheric fluctuations average out
Explanation
ConceptTwinkling (scintillation) is due to random refraction by atmospheric turbulence. A point-like source fluctuates strongly.
ReasonPlanets subtend a finite angle; light from different parts averages through the turbulent cells, so brightness appears steady.
Final AnswerPlanets are much closer and have appreciable apparent disks, so atmospheric fluctuations average out