Any elliptical orbit has two apsides.
Similarly, in the orbit of the earth or another planet around the sun, the perihelion is the point of closest approach and the aphelion is the point of farthest recession. In the orbit of the stars in a binary star system, the periastron is the point of closest approach and the apastron the point of farthest recession. This line may precess because of gravitational influences of other bodies or relativistic effects. Licensed from Columbia University Press. All rights reserved.