gs1medium

Consider the following phenomena:

  1. 1.Size of the sun at dusk
  2. 2.Colour of the sun at dawn
  3. 3.Moon being visible at dawn
  4. 4.Twinkle of stars in the sky
  5. 5.Polestar being visible in the sky

Which of the above are optical illusions?

  1. A.1, 2 and 3
  2. B.3, 4 and 5
  3. C.1, 2 and 4
  4. D.2, 3 and 5
▶ Answer & Explanation

Correct answer: C. 1, 2 and 4

The apparent larger size of the sun at dusk or dawn is an optical illusion due to the relative comparison with terrestrial objects and atmospheric refraction. Similarly, the reddish colour of the sun during sunrise and sunset is caused by the scattering of sunlight by atmospheric particles, making shorter wavelengths scatter away. The twinkling of stars is due to the atmospheric refraction of starlight as it passes through various layers of the atmosphere with different densities and temperatures. The moon and polestar are actual celestial bodies visible due to their position and luminosity, not illusions.

Source: UPSC gs1 2013

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