Astrophysics (Index)About


(gravitational primary, primary body, central body)
(central body of a system such as the Sun in the solar system)

A use of the term primary within astronomy is to indicate a central body of a gravitationally-bound system that has a substantial majority of the system's total mass, e.g., sufficient mass that the barycenter is within the body itself. The Sun is the primary of the solar system and the Earth is the primary of the Earth/Moon system. However, the term is not generally used for the supermassive black hole at the center of the Milky Way, which does not have nearly such a high fraction of the galaxy's mass.

Further reading:

Referenced by pages:
Keplerian disk
Kepler's laws
Roche limit
SS 433