The twinkling of a star is due to :

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atmospheric reflection of starlight.

atmospheric refraction of starlight.

continuous change in the position of the star.

oscillation of starlight.

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This question was previously asked in

UPSC CDS-1 – 2022

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The twinkling of a star is due to atmospheric refraction of starlight.

Starlight travels through the Earth’s atmosphere before reaching our eyes. The atmosphere is composed of layers with different densities and temperatures, causing the refractive index to vary continuously. As starlight passes through these varying layers, it is refracted or bent slightly in different directions. This continuous change in the path of light causes fluctuations in the apparent brightness and position of the star, leading to the twinkling effect.

Planets, being much closer, appear as discs rather than point sources of light. Although their light is also refracted, the light from different parts of the disc averages out the effect, which is why planets do not typically twinkle as much as stars. Reflection (bouncing light off a surface) is not the cause of twinkling.

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