Please explain clearly about atmospheric refraction?

Asked by Sanjay Sagar | 6th Mar, 2012, 08:19: PM

Expert Answer:

Stars twinkle because the star light reaching our eyes increases and decreases continuously due to atmospheric refraction. Light from a star travels first in vacuum, and then enters into earth's atmosphere. As optical density of air increases towards the surface of earth, therefore, light from the star travels from rarer to denser layers, bending every time towards normal. Moreover, different layers of atmosphere are mobile. The temperature and optical density of layers of atmosphere changes continuously. Therefore, apparent position of the star and amount of light from the star reaching our eyes, both change continuously. This leads to twinkling of stars.
 
Planets appear bigger than the stars as planets are closer to earth. A planet can be considered to be made up of a no. of point sources of light. Due to atmospheric refraction, when some of the point sources look brighter, others appear dimmer. Therefore, on the whole over all brightness of a planet remains the same always. Hence, the planets do not appear to twinkle.

Answered by  | 6th Mar, 2012, 08:44: PM

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