How did astronomers discover the relationship between spectral type and mass for main sequence stars?

Question

Quizplus · Accepted Answer

Astronomers discovered the relationship between spectral type and mass for main sequence stars by measuring the masses and spectral types of main-sequence stars in binary systems. By observing the orbits of binary stars, astronomers can determine the masses of the stars and also measure their spectral types, allowing them to establish the relationship between spectral type and mass for main-sequence stars.

How Did Astronomers Discover the Relationship Between Spectral Type and Mass