Definitions for "Periastron"
That point, in the real or apparent orbit of one star revolving around another, at which the former is nearest to the latter.
means the least separation of the principals in a binary. Similarly, its homologues are perigee and perihelion when orbiting the Earth or the Sun. Elsewhere, the term pericentron is used to describe the closest approach between two bodies in orbit.
The near point of the orbit of a body to the star around which it is orbiting.