Ans.
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In the atmosphere, there are different layers of air with different
refractive indices which keep on changing as the physical conditions of
air are not stationary.
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When we observe any object through this air, the light coming from
them refract randomly due to which the apparent position of the object
fluctuates.
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The large scale effect of this phenomenon is the twinkling of stars,
advanced sunrise and delayed sunset.
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Due to change in the refractive index of atmosphere, the intensity of
light that reaches our eyes from the stars varies and hence the stars
appear twinkling at night.
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Advanced sunrise occurs as a ray of light from the sun enters the
earths atmosphere, it follows a curved path due to refraction before
reaching to the observer.
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It appears to the observer as if the rays are coming from the position.
Where the sun is seen by the observer, hence the sun is seen earlier
before it reaches the horizon.
