Two stars have the same luminosity (or absolute magnitude). One star is spectral class B and the other is spectral class K. From this information, one knows that the
A) K-type star is larger than the B-type star.
B) B-type star is larger than the K-type star.
C) B-type star is hotter but can be larger, smaller, or the same size as the K-type star.
D) K-type star is hotter but can be larger, smaller, or the same size as the B-type star.

Question

Quizplus · Accepted Answer

Given the same luminosity, the cooler K-type star must be larger to compensate for its lower temperature compared to the hotter B-type star, as luminosity is a function of both size and temperature.

Two Stars Have the Same Luminosity (Or Absolute Magnitude)