Question

Stars twinkle but planets do not twinkle because
A.) Stars emit their own light but planets receive light from the stars.
B.) Stars do not form a part of the solar system.
C.) Stars from a point source of light while planets are considered as a collection of a large number of point sources.
D.) During refraction of star light from the atmosphere, star light bends more towards the normal as compared to other planets.

Answer 1

Hint: The phenomenon of refraction of light is what dictates this question. Try to think what can cause the stars to twinkle. Twinkling can be considered a result of a continuous small change in the apparent source of the light received.

Complete step by step answer:
Refraction works on the basis of different densities of air. If there is a change in the densities of different layers of air, the light passing through them does not move in a straight line. There is an atmosphere around earth which is filled with different gases. Because of the presence of different gases there is a difference in density in between layers present in the atmosphere. Outside of this atmosphere, there is vacuum. So, any light coming from outside the atmosphere is going to be subjected to bending when it enters the Earth’s atmosphere. So, as a result, when the light from the star travels through vacuum before reaching earth’s atmosphere, it travels in a straight line. However, when it reaches the Earth’s atmosphere, it bends and as the density of the layers of atmosphere keeps on changing, it keeps on bending till it reaches our eye. As a result of the continuous bending of light, it appears to us as if the stars twinkle.

Note: Read the options and you will realize that some of them are incorrect factually and thus cannot be the answer. For example, option C. is incorrect as stars are not a point source and planets are not a collection of a large collection of point sources. But, reflect light from stars.