Also found in: Thesaurus, Medical, Encyclopedia, Wikipedia.
Related to periastron: periapsis, Pericenter
n. pl. per·i·as·tra (-trə)
The point at which an object is closest to the center of mass of the star it is orbiting.
(Astronomy) 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
The point in the orbit of an object around a star at which the object is at its closest to the star.