Center of mass

In astronomy, the barycenter is the center of mass of a system of two or more bodies. For the purposes of most calculations, the system can be considered to be concentrated at the position of the barycenter, with a total mass equal to the sum of the masses of the individual objects. The barycentric radial velocity of an object, such as a star, as measured by a terrestrial observer is calculated relative to the center of mass of the Solar System. This is slightly different from the heliocentric velocity of such a star, which is centered on the Sun and varies slightly with time according to the position of the planets (since the motion of the planets produces slight changes in the Solar System’s barycenter).