Astrophysics (index)about

primary

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

The term primary is used for the central body of a gravitationally-bound system if it has the majority of the 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, it 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.


(astronomy,mass)
http://en.wikipedia.org/wiki/Primary_(astronomy)

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

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