Consider the following statements Assertion A The apparent position of the star on earth is sl...........

Geography Space

Consider the following statements.

Assertion (A): The apparent position of the star on earth is slightly different from its actual position.

Reason (R): The starlight, on entering the earth’s atmosphere, undergoes refraction continuously before it reaches the earth.

In the context of the above, which of these is correct?

A is correct, and R is an appropriate explanation of A.

A is correct, but R is not an appropriate explanation of A.

A is correct, but R is incorrect.

Both A and R are incorrect.

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Explanation:

Justification: The atmospheric refraction occurs in a medium of gradually changing refractive index. Since the atmosphere bends starlight towards the normal, the apparent position of the star is slightly different from its actual position.
The star appears slightly higher (above) than its actual position when viewed near the horizon.
• Further, this apparent position of the star is not stationary, but keeps on changing slightly, since the physical conditions of the earth’s atmosphere are not stationary.
• Since the stars are very distant, they approximate point-sized sources of light.
• As the path of rays of light coming from the star goes on varying slightly, the apparent position of the star fluctuates and the amount of starlight entering the eye flickers – the star sometimes appears brighter, and at some other time ,fainter, which is the twinkling effect