Question

Why are stars considered as point sources of light while planets are considered as extended sources of light?​

Answer 1

Stars twinkle because they are so far from Earth that they appear as point sources of light easily disturbed by Earth's atmospheric turbulence which acts like lenses and prisms diverting the light's path while the planets are much closer to the earth and are thus seen as extended sources where as stars are very distant, the approximate point-sized sources of light.

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