Do you know, What is Atmospheric Refraction ??


Do you know, What is Atmospheric Refraction ??

Let’s discuss on it ,

1. Atmospheric Refraction

Atmospheric Refraction

Since in the atmosphere, we have air everywhere. But all the air in the atmosphere is not at the same temperature. Some of the air layers of the atmosphere are cold whereas other air layers of the atmosphere are comparatively warm (or hotter). Now,

  • the cooler air layers of the atmosphere behave as optically denser medium for light rays whereas
  • the warmer air layers (or hotter air layers) of the atmosphere behave as optically rarer medium for the light rays.

So, in the same atmosphere we have air layers having different optical densities  and when light rays pass through the atmosphere having air layers of different optical densities, then refraction of light takes place. So, the refraction of light caused by the earth’s atmosphere (having air layers of varying optical densities) is called atmospheric refraction.

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1.1  Some of the optical phenomena in nature which occur due to the atmospheric refraction of light —-

1.1.1  Twinkling of Stars: When the light coming from a star enters the earth’s atmosphere, it undergoes refraction due to the varying optical densities of air at various altitudes. The atmosphere is continuously changing.  The continuously changing atmosphere refracts the light from the stars by different amounts from one moment to the next.

  • When the atmosphere refracts more star-light towards us, the star appears to be bright and
  • when the atmosphere refracts less star-light, then the star appears to be dim.

In this way, the star-light reaching our eyes increases and decreases continuously due to atmospheric refraction. And the star appears to twinkle at night.

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1.1.2  Planets do not twinkle: The stars are very, very far off that’s why the stars appear very, very small to us. So, stars can be considered to be point sources of light.

On the other hand, the planets appear to be quite big to us (because they are much nearer to the earth). So, a planet can be considered to be a collection of a very large number of point sources of light.

The dimming effect produced by some of the point sources of light in one part of the planet is nullified by the brighter effect produced by the point sources of light in its other Thus, on the whole, the brightness of a planet always remains the same and hence it does not appear to twinkle.

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