INSIGHT UPSC QUIZ

Science & Technology General Science
Q.

Which of the following phenomena are caused due to ‘atmospheric refraction’?

1. Flickering of objects seen through a turbulent stream of hot air rising above a fire.

2. The reddening of the sun at sunrise and the sunset.

3. The apparent flattening of the Sun’s disc at sunrise and sunset.

4. The Sun is visible to us about 2 minutes before the actual sunrise, and about 2 minutes after the actual sunset.

Select the correct answer using the code given below.

Explanation:

ANSWER: (D) 

  • The apparent random wavering or flickering of objects seen through a turbulent stream of hot air rising above a fire or a radiator is caused due to atmospheric refraction. 
  • The air just above the fire becomes hotter than the air further up. The hotter air is lighter (less dense) than the cooler air above it, and has a refractive index slightly less than that of the cooler air. 
  • Since the physical conditions of the refracting medium (air) are not stationary, the apparent position of the object, as seen through the hot air, fluctuates. 
  • This wavering is thus an effect of atmospheric refraction (refraction of light by the earth’s atmosphere) on a small scale in our local environment. 
  • The twinkling of stars is a similar phenomenon on a much larger scale.
  • The Sun is visible to us about 2 minutes before the actual sunrise, and about 2 minutes after the actual sunset because of atmospheric refraction. 
  • The apparent flattening of the Sun’s disc at sunrise and sunset is also due to the same phenomenon.
  • The reddening of the sun at sunrise and the sunset is due to the scattering of light.

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