The apparent position of a star keeps on changing slightly because:

Correct option is B

The correct answer is (B) the physical conditions of the atmosphere keep changing.

Explanation:

The apparent position of a star changes slightly due to a phenomenon called atmospheric refraction, which occurs because the Earth's atmosphere is not uniform. The refractive index of the atmosphere varies due to:

• Temperature changes: Different layers of the atmosphere have varying temperatures, causing the density and refractive index to fluctuate.
• Air pressure variations: Changes in air pressure also affect the density of the atmosphere.
• Wind and turbulence: Movement of air masses introduces irregularities, bending the path of starlight inconsistently.

This constant change in atmospheric conditions causes the light from the star to refract slightly differently, making the star appear to "twinkle" or change position.