Which of the following happens due to atmospheric refraction? I. Twinkling of stars II. Advanced sunrise and delayed sunset

Which of the following happens due to atmospheric refraction? I. Twinkling of stars II. Advanced sunrise and delayed sunset Correct Answer Both I and II

The correct answer is Both I and II.

Key Points

• The refraction of light by the Earth’s atmosphere is known as the atmospheric refraction of light.
• The phenomena of atmospheric refraction are:
  • twinkling of stars
  • early Sunrise
  • delayed sunset
  • stars seem higher than actual height.

Important Points

• Twinkling of stars: 
  • As the movements of air and convection currents cause a change in the density of the layers of air.
  • As a result, the position of the image of the star goes on to change after every short interval.
  • These different positions of the images formed at short intervals of time give the impression that the star is twinkling. 
• Advanced sunrise and delayed sunset
  • ​The Sun is visible a little before the actual sunrise and until a little after the actual sunset due to the refraction of light through the atmosphere.
  • The layers of air nearer to earth are denser than those above it.
  • At sunrise and sunset when the sun is below the horizon, the light rays starting from the sun are incident on these layers.
  • They pass through successively denser layers and thus get bent more and more towards the normal until they fall upon the eye of the observer.
  • To the observer, these rays appear to come from S’ which is above the horizon. It is for this reason that the sun is visible to us a little before it rises above the horizon and so also till a little later it sets below the horizon.
  • The difference in time is about 2 minutes each for an early rise and late setting of the Sun.