Stars twinkle because

Answers (1)

The twinkling of a star is due to atmospheric refraction of starlight. The starlight, on entering the earth's atmosphere, undergoes refraction continuously before it reaches the earth. Since the temperature of air and its humidity are not the same everywhere in the atmosphere, the refractive index of air varies between different masses (or pockets) of air, even at the same altitude. So we can say the atmospheric refraction occurs in a medium of gradually changing refractive index.

  1. When a ray of light passes through such a pocket of air, it bends due to refraction towards the normal, so the apparent position of the star is slightly different from its actual position. 

  2. The star appears slightly higher (above) than its actual position when viewed near the horizon. Further, this apparent position of the star is not stationary, but keeps on changing slightly as the physical conditions of the earth's atmosphere are not stationary. 

  3. As the path of rays of light coming from the star goes on varying slightly, the apparent position of the star fluctuates and the amount of starlight entering the eye flickers - the star sometimes appears brighter, and at some other time, fainter, which is the twinkling effect.

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