APSES

(Yunanca köken — orijinale bakınız.) The t\vo points of the orbit of a planet or satellite, at which it is moving at right angles to the straight line joining it with the primary. These two points of the orbit are the two extremities of the major axis, or the points at which a planet is at its greatest and least distance from the sun. The point at the greatest distance is called the higher apsis; that at the least is called the lower apsis; consequently, the higher apsis corresponds with the aphelion, and the lower apsis with the perihelion. The line joining these two points, which is the transverse axis of the orbit, is called the line of the apsides. It has a slow angular motion in the plane of the planet's orbit; and the time which the planet employs in completing a revolution with regard to its apsides is called the anomalistic period. {See Aphelion. Anomajly.) [s. 82]