Stars twinkle because:

Correct option is C

The correct answer is (c) the refractive index of the different layers of the earth's atmosphere changes continuously

Explanation:
• Twinkling of stars is due to atmospheric refraction.
• The Earth's atmosphere has layers of varying densities and temperatures, which are constantly moving.
• As a result, the refractive index changes, causing the path of light from the star to vary slightly, making the star appear to flicker or twinkle.

Information Booster:
• Planets do not twinkle because they are much closer to Earth and act as extended sources of light, averaging out the refraction effects.
• Refraction also causes the star to appear slightly higher than its actual position.

Additional Knowledge:
Motion of earth (Option a)
• Causes the stars to appear to move across the sky, but not the twinkling.
Distance changes (Option b)
• Changes are negligible on the scale required for twinkling.
Intensity changes (Option d)
• Most stars have relatively constant luminosity; the perceived change is purely an atmospheric effect.

So the correct answer is (c)