Astronomy, a term used indifferently for either of the two points of a planet's orbit, where it is at the greatest or least distance from the sun or earth; and hence the line connecting those points is called the line of the apsides. The word is Greek, and derived from ἀπόσις, I connect. The apsis, at the greatest distance from the sun, is called the aphelion, and at the greatest distance from the earth the apogee; while that at the least distance from the sun is termed the perihelion, and at the least distance from the earth the perigee.