[uh-pas-truhn, -tron]
noun, plural apastra [uh-pas-truh] . Astronomy.
the point at which the stars of a binary system are farthest apart (opposed to periastron ).

< Neo-Latin < Greek ap- ap-2 + ástron star, constellation; on the model of apogee

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apastron   (ə-pās'trən)  Pronunciation Key 
  1. The point at which two stars orbiting each other in a binary star system are farthest apart.

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

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