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What is atmospheric refraction? Use this phenomenon to explain the following natural events:(a) Twinkling of stars(b) Advanced sun-rise and delayed sun-set. Draw diagrams to illustrate your answers.
The refraction of light due to the earth's atmosphere is called atmospheric refraction. Atmospheric refraction is caused by the bending of light rays when they pass through the layers of the earth's atmosphere having different optical densities.
(a) Stars twinkles due to atmospheric refraction.
When the light coming from the star enters the earth's atmosphere, it gets refracted (bent), due to varying optical densities of air at various altitudes. The atmosphere keeps changing continuously due to which light from the stars gets refracted by different amounts from one moment to the next.
When the atmosphere refracts more star-light towards us, the star appears to be bright, whereas when it refracts less star-light, then it appears to be dim. In this way, the star-light reaching our eyes increases and decreases continuously due to refraction, and thus star appears to twinkle at night.
Image is posted for reference only
(b) Advanced sun-rise and delayed sun-set is also due to atmospheric refraction.
Due to the refraction of sunlight caused by the atmosphere, we can see the sun 2 minutes before it's actually above the horizon (advanced sunrise), and 2 minutes even after the actual sunset (delayed sunset).
This happens because when the sun is slightly below the horizon, then the sun's light coming from the less dense air to more dense air is refracted downwards as it passes through the atmosphere. Thus, due to this atmospheric refraction, the sun appears to be raised above the horizon when actually it is slightly below the horizon.
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