Apastron
| In a binary star system, each star moves around the other in an elliptical orbit. The point of maximum separation between the two stars is called the apastron. This position is the same as the apoapsis of the orbit, but specifically refers to orbits around other stars. The point of closest approach between the two stars is the periastron. |
Viewed from a reference frame where one of the stars is at rest, the secondary star moves in an elliptical orbit. The secondary star is at apastron when the two stars have their greatest separation.
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