[ per-ee-as-truh n, -tron ]
/ ˌpɛr iˈæs trən, -trɒn /

noun, plural per·i·as·tra [per-ee-as-truh] /ˌpɛr iˈæs trə/. Astronomy.

the point at which the stars of a binary system are closest (opposed to apastron).

Origin of periastron

1850–55; < peri- + Greek ástron star; modeled on perihelion

Related forms

per·i·as·tral, adjective Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for periastron

  • At least, the periastron effects; there was another angle to it.

    Oomphel in the Sky|Henry Beam Piper

British Dictionary definitions for periastron


/ (ˌpɛrɪˈæstrɒn) /


astronomy the point in the orbit of a body around a star when it is nearest to the star, esp applied to double-star systems
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Science definitions for periastron


[ pĕr′ē-ăstrən, -trŏn ]

Plural periastra

The point at which an object, such as a planet or comet, is closest to the center of mass of the star it is orbiting. Compare apastron.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.