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).

---

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

---

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

---

Other Word Forms

Derived Forms

• periastral
  adjective

Inflected Forms

Nouns

• periastra
  plural

Etymology

Origin of periastron

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

Example Sentences

See Examples For:

periastron

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 eccentricity of their orbit approaches in form that of Faye’s comet, which travels round the Sun; consequently the stars, when at apastron, are twice their periastron distance.

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

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

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

From Oomphel in the Sky by Piper, H. Beam

There was a project to provide shelters for the periastron storms set up ten years ago.

From Oomphel in the Sky by Piper, H. Beam