# How are the masses of stars measured?

Determination of the masses of stars turned out to be possible on the basis of the application of Kepler’s third law to binary stars. This law, after its derivation by Newton as a consequence of the law of universal gravitation, has a refined form

(m + M) T ^ 2 / a ^ 3 = 4n ^ 2 / C

Where T is the period of circulation of bodies of masses m and M around a common center of mass; a is the average distance between bodies. Using Kepler’s third law, from the measured values of the binary’s orbital period and the average distance a between stars, we can calculate the sum of the masses of the binary’s components. After determining L from the orbits of the stars, the position of the center of mass of the system, we can find the mass of each of the stars.