periastron

American  

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

noun

Astronomy.

periastra plural

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

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periastron British  

/ ˌpɛrɪˈæstrɒn /

noun

1. 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

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periastron Scientific  

/ pĕr′ē-ăs′trən,-trŏn /

periastra plural

1. 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.

2. Compare apastron

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Other Word Forms

• periastral
  adjective

Etymology

Origin of periastron

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

Example Sentences

As the stars move closer, their orbital motion changes more rapidly, including the position of their closest approach, known as periastron.

From Science Daily • Apr. 19, 2026

The pair travel in an orbit from fourteen to forty-two times the radius of the Earth’s orbit; so that when at apastron they are three times as distant from each other as when at periastron.

From The Astronomy of Milton's 'Paradise Lost' by Orchard, Thomas Nathaniel

The last periastron was ninety years ago, and we've only been here for sixty-odd; all we have is verbal accounts from memory from the natives, probably garbled and exaggerated.

From Oomphel in the Sky by Piper, H. Beam

It seems that the government here knew all about the weather conditions they could expect at periastron, and had made plans for them.

From Oomphel in the Sky by Piper, H. Beam

These orbs complete a revolution in 180 years, and when in apastron are seventeen times more remote from each other than when at periastron.

From The Astronomy of Milton's 'Paradise Lost' by Orchard, Thomas Nathaniel