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Q: The apparent position of a star keeps on changing slightly because:
  • A. the atmosphere scatters star light
  • B. the physical conditions of the atmosphere keep changing
  • C. the atmosphere consists of a mixture of gases
  • D. the physical conditions of the atmosphere are stationary
Correct Answer: Option B - The apparent position of a star keeps on changing because the refractive index of the different layers of gases changes in the atmosphere due to the change in physical conditions (temperature & pressure) of gases. Change in refractive index in atmospheric gases bents the light rays, coming from the star, many times and this in the reason behind the apparent position change of a star.
B. The apparent position of a star keeps on changing because the refractive index of the different layers of gases changes in the atmosphere due to the change in physical conditions (temperature & pressure) of gases. Change in refractive index in atmospheric gases bents the light rays, coming from the star, many times and this in the reason behind the apparent position change of a star.

Explanations:

The apparent position of a star keeps on changing because the refractive index of the different layers of gases changes in the atmosphere due to the change in physical conditions (temperature & pressure) of gases. Change in refractive index in atmospheric gases bents the light rays, coming from the star, many times and this in the reason behind the apparent position change of a star.