Class 10 Physics Human Eye and Colourful World Atmospheric Refraction

Atmospheric Refraction

Twinkling of Stars

  • The twinkling of stars is also due to atmospheric refraction.
  • The air in the earth's atmosphere is such that it has increasing refractive index
  • When starlight enters earth's atmosphere it undergoes multiple refraction continuously before it reaches the earth
  • Because of the increasing refractive index, the starlight bends downwards (ie towards the normal) and thereby the apparent position of the star is slightly higher than its actual position.
  • Also, this apparent position of the star is not fixed. It keeps on changing slightly since the atmospheric conditions of the earth keep varying
  • But however the stars are so distant that they appear fixed to the naked eye

Early sunset and Delayed sunrise

  • Atmospheric Refraction is the same reason that the sun is seen about 2 minutes before actual sunrise and is seen for about 2 minutes after sunset.
  • The actual position of the sun is slightly shifted from the actual position of the sun

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