Question

4. Assertion: The twinkling of a star is to atmosphere refraction of star light.
Reason: The refraction of light by the earth's atmosphere is due to the gradually changing
refractive index of air layers.
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Answer 1

Answer: The refraction of light by the earth's atmosphere is due to the gradually changing refractive index of air layers.

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Answer 2

The correct answer is (a) Both  assertion and reason are correct and the reason is the correct explanation of the assertion

• As the sunlight passes from the atmosphere with varying densities, it undergoes refraction.
• The refraction of starlight is done as per the refractive index of the air layers.
• Now, the air is continuous in motion and air densities are subject to change. When the next ray of light comes, then it suffers different bending.
• Owing to this reason, the position of the star seems to be changing slightly, hence the stars appear to be twinkling.
• Thus, the stars twinkle because of the atmospheric refraction of starlight and the gradually changing refractive index of air layers. Thus, both the statements are correct and the reason correctly explains the assertion.