The Sun's absolute magnitude is about +5. The brightest stars in the sky have absolute magnitudes of about -10. What is the luminosity of these stars compared with that of the Sun, assuming that they have similar spectral light distributions?
A) 1 million times less
B) 5 times less
C) 1 million times greater
D) 15 times greater

Question

Quizplus · Accepted Answer

The luminosity of a star compared to another can be calculated using the difference in their absolute magnitudes. A difference of 5 magnitudes corresponds to a factor of 100 in brightness. Since the brightest stars have absolute magnitudes about 15 magnitudes brighter than the Sun's (+5 to -10 = 15), they are $100^{(15/5)} = 100^3 = 1,000,000$ times more luminous than the Sun.

The Sun's Absolute Magnitude Is About +5