The twinkling of stars, known as stellar scintillation, is caused by atmospheric refraction. As starlight passes through different layers of the atmosphere with varying densities and temperatures, the light is bent multiple times. Since the atmosphere is constantly moving due to winds and turbulence, the position and brightness of the star appear to shift rapidly to our eyes. ANSWER: (B) Atmospheric Refraction
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When light from a distant star enters our atmosphere, it travels through air of changing refractive indices. These changes are driven by temperature fluctuations and air movement. Because stars are essentially point sources of light, even a small amount of bending (refraction) causes the light to hit the eye from slightly different angles. This causes the star to seem to “dance” or change color and intensity. Planets, being closer and appearing as tiny disks rather than points, twinkle much less because the light from different parts of the disk averages out the refractive interference.