Question

Which phenomenon is responsible for the twinkling of stars?
(A) Atmospheric reflection
(B) Atmospheric refraction
(C) Reflection
(D) Total internal reflection

Answer 1

Hint: The atmosphere of Earth is divided into different layers – Troposphere, Stratosphere, Mesosphere, Thermosphere, and Exosphere. It is important for this problem to understand that every layer of the atmosphere has different density and temperature.

Complete step by step answer:
The stars twinkle due to our atmosphere. If we go beyond our atmosphere, then stars do not twinkle. When our astronaut goes into space, they find the stars do not twinkle.
Because of the atmosphere, two things happened – first, the position of stars seen by us shifts from the original position, This means the light coming from stars bend at the atmosphere; This is because the light is entering from vacuum to atmosphere, so the speed of light slows down, and refraction occurs. So the shifting position of stars is due to atmospheric refraction.
Second the stars twinkle. When light bends in the atmosphere, then light does not come to us in a straight path. It always changes its path. This light travels a curved path, and this is because our atmosphere is not of uniform density. Every level of the atmosphere has a different density because of these changes in density; the speed of the light changes at a different level of atmosphere. The light rays coming from stars continuously change their path because the density of the atmosphere changes continuously, so the number of light rays that fall into our eyes is also changing because of which the brightness of light fluctuates. Thus the stars also twinkle due to atmospheric refraction.

Correct answer is (B).

Note: The twinkling can only be observed for the stars, since their distance from the Earth is very far, making them appear like a point object. This is not the case for other planets or moons, since they are relatively closer to the Earth than the stars. This fact, also, serves as a means to identify planets from the stars.