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A mass-luminosity relation relates a star's mass with its luminosity:
L / LSun = ( M / MSun )a
Such a relation is thought to hold (roughly) within various classifications of stars: a value of a = 3.5 is often used for a very rough estimate for main sequence stars (which demonstrates the huge variation found in the luminosity of stars):
| solar masses | solar luminosities suggested by a = 3.5 |
| 0.5 | 0.088 |
| 2 | ~11 |
| 10 | ~3200 |
| 20 | ~36,000 |
| 50 | ~880,000 |
Better values of a can be determined for classes of stars, e.g., based on the characteristics of their convection, and/or their general mass range. Stars close to the Eddington luminosity have a close to 1. Eclipsing binaries and parallax measurements help confirm the relation(s).
More reliable relations have been devised by including additional factors, e.g., age and/or radius.
Analogous mass-luminosity relations have been determined for galaxies, which offer means of estimating the masses of distant galaxies.