- One of the two points of an orbit, as of a planet or
satellite, which are at the greatest and least distance from the
central body, corresponding to the aphelion and perihelion of a planet,
or to the apogee and perigee of the moon. The more distant is called
the higher apsis; the other, the lower apsis; and the line joining
them, the line of apsides. - In a curve referred to polar coordinates, any point for
which the radius vector is a maximum or minimum. - Same as Apse.