apastron

noun, plural ap·as·tra [uh–pas-truh] /əˈpæs trə/. Astronomy.

1. the point at which the stars of a binary system are farthest apart (opposed to periastron).

1. The point at which an object, such as a planet or comet, is farthest from the center of mass of the star it is orbiting. Compare periastron.