Twinkling of stars is due to

particular frequencies of the starlight.

reflection of starlight from the oceanic surface.

atmospheric refraction of starlight.

magnetic field of Earth.

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This question was previously asked in

UPSC NDA-1 – 2021

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The twinkling of stars is caused by the Earth’s atmosphere. As starlight travels through the atmosphere, it passes through layers of air with varying densities and temperatures. This causes the light to be refracted (bent) multiple times. Since these layers are constantly moving and mixing due to atmospheric turbulence, the path of the starlight changes slightly from moment to moment. This results in fluctuations in the apparent brightness and position of the star, which we perceive as twinkling. This phenomenon is called atmospheric refraction.

Stars appear as point sources of light because they are very distant. The light from a point source is more susceptible to the bending effects of atmospheric turbulence compared to the light from extended sources like planets (which appear as discs). Planets do not typically twinkle for this reason.

Refraction is the bending of light as it passes from one medium to another or through a medium with varying properties. The refractive index of air changes with temperature and pressure, which vary throughout the atmosphere.

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