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Railways PYQCBT 1 2016

RRB NTPC · Question 45

The theory behind stars twinkling is that

  1. The refractive index of the different layers of earth’s atmosphere changes continuously; consequently the position of the star’s image changes with time.

  2. The intensity of light emitted by them changes with time

  3. The light from the star is scattered by the dust particles and air molecules in the earth’s atmosphere

  4. The distance of the stars from the earth changes with time

Show answer & explanation

Answer: (A) The refractive index of the different layers of earth’s atmosphere changes continuously; consequently the position of the star’s image changes with time.

Explanation

Starlight passes through layers of air whose temperature and density, and so refractive index, keep changing. The light is bent by varying amounts, so the star's apparent position and brightness flicker.