Stars twinkle because:
- AOf the motion of the Earth
- BThe distance of the stars from the Earth changes with time
- CThe refractive index of the different layers of the Earth's atmosphere changes continuously
- DThe intensity of the light emitted by them changes with time
Show answer and explanation
Correct answer: (c) The refractive index of the different layers of the Earth's atmosphere changes continuously
Explanation
Stars twinkle because of atmospheric refraction. Starlight passes through layers of air whose temperature and density keep changing, so their refractive index changes continuously. The starlight is bent by slightly different amounts from moment to moment.
Stars are so far away that they act as point sources, so these small changes make their apparent position and brightness flicker. Planets are much nearer and look like small discs. The flicker from different points of the disc averages out, so planets do not twinkle.