Question

Which of the following points can be attributed as a reason for deviation of apparent position of a star from its actual position?

• A. Stars are farther than the Sun
• B. Starlight undergo refraction while entering atmosphere
• C. Changing refractive index of atmosphere
• D. Effect of moonlight

Answer 1

Answer: (B), (C)

The correct options are
B

Starlight undergo refraction while entering atmosphere

C

Changing refractive index of atmosphere

It is due to the atmospheric refraction of starlight. We know that the temperature and density of the different layers of atmosphere keep varying.

So, when a light from the distant star(a point source of light) enters the earth’s atmosphere, it undergoes refraction continuously due to the changing refractive index (i.e. from rarer to denser) and thus the light rays keep bending in earth's atmosphere. Due to this, the apparent position of star appears different from the actual position.