The apparent position of the star is always__________.
(A) Fluctuating
(B) Same
(C) Predictable
(D) Increasing

Hint: The light coming from star suffers atmospheric refraction. Atmospheric Refraction is a phenomenon in which the light ray gets deviated from a straight path while passing through the atmosphere as a result of the change in air density due to which the velocity of the light gets changed. This phenomenon is responsible for the twinkling of the star.

Complete step by step answer:
The apparent position of a star is always fluctuating due to atmospheric refraction due to the presence of the earth’s atmosphere between the earth and the star.
The light ray gets deflected towards the normal when it passes through a rarer medium to denser medium and when it passes through a denser medium to a rarer medium the light ray gets deflected away from the normal.
Considering this, we can say that the light ray position changes according to the atmosphere, So sometimes it will propagate towards the normal and sometimes away from the normal. So we can say that its position will fluctuate.

$\therefore $ The apparent position of the star is always Fluctuating. Hence, option (B) is the correct option.

Additional information:
When we see the star from the earth’s surface the light coming from the star gets refracted due to the presence of the earth’s atmosphere between the star and us. Due to this atmospheric refraction, the light coming from the star towards earth undergoes refraction due to which it’s apparent brightness and position keeps on changing. As a result of this refraction, we see stars as twinkling and changing their position continuously. This phenomenon is referred to as scintillation.

Note:
- The fluctuation increases if the refractive index decreases and decreases when the refractive index increases.
- When a ray of light passes through one medium to another medium then it changes its direction this change in direction is due to refraction.
- When a ray of light passes from a denser medium to a rarer medium its speed increases and when it passes through a rarer to denser medium its speed decreases.