A star has absolute luminosity equal to that of the Sun (1.5 × 10⁸ km from the Earth) but is 10 pc away from the Earth. By what factor will it appear dimmer than the Sun? A)2 × 10^-⁹ B)2 × 10^-¹¹ C)2 × 10^-¹³ D)2 × 10^-¹⁵ E)2 × 10^-¹⁷

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Quizplus · Accepted Answer

The apparent brightness of a star is inversely proportional to the square of its distance. The Sun is 1 AU (1.5 × 10^8 km) away, and 10 pc is about 2.06 × 10^6 AU. The factor is (1 AU / 2.06 × 10^6 AU)^2 ≈ 2 × 10^-13.

A Star Has Absolute Luminosity Equal to That of the Sun