What causes the twinkling of stars?
Last updated Jun 24, 2026
Correct Answer:
Option A —
Atmospheric refraction of starlight
Why do stars twinkle?The phenomenon, scientifically known as stellar scintillation, occurs because the Earth's atmosphere is not a uniform vacuum. Instead, it consists of multiple layers of air with varying temperatures and densities.
Varying Refractive Indices: As starlight enters the Earth's atmosphere, it passes through these different layers. Cold air is denser than warm air and has a higher refractive index.
Constant Motion: The atmosphere is turbulent; air is constantly moving and changing temperature. This means the refractive index of the medium through which the light travels is always shifting.
Path Bending: Because the light is being refracted (bent) repeatedly and randomly, the apparent position of the star shifts slightly.
Fluctuating Intensity: This bending causes the light to sometimes focus more toward your eye and sometimes away, making the star appear to change in brightness and position rapidly. This is what we perceive as "twinkling."
Why don't planets twinkle?
Planets are much closer to Earth than stars. While a star is so distant that it appears as a single point source of light, a planet appears as a extended source (a tiny disk).
Even though the light from different points on the planet's disk is being refracted, the variations tend to cancel each other out. When one point dims, another might brighten, resulting in a steady overall brightness.
Answer verified by Quintessence Classes faculty — Karan Nagar, Srinagar.
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