In astronomy, the distance to a visual binary star may be estimated from the masses of its two components, the angular size of their orbit, and the period of their orbit about one another.
To calculate a dynamical parallax, the angular semi-major axis of the orbit of the stars is observed, as is their apparent brightness.
By using Newton's generalisation of Kepler's Third Law, which states that the total mass of a binary system multiplied by the square of its orbital period is proportional to the cube of its semi-major axis,[2] together with the mass–luminosity relation, the distance to the binary star can then be determined.
Then, using Kepler's laws of celestial mechanics, the distance between the stars is calculated.
These masses are used to re-calculate the separation distance, and the process is repeated.