The plural form of apse.
The points where the major axis of an elliptical orbit meets the orbital path. The periapse (or pericentre) is the point of closest approach to the primary body; the apoapse (or apocentre) is the point of greatest distance.
The points in the orbit of a planet or moon which are the nearest and farthest from the center of attraction. In the Earth's orbit these are called perihelion and aphelion, and in the Moon's orbit, perigee and apogee. The line passing through the apsides of an orbit is called the line of apsides.
Plural of Apsis. According to The Aphorisms of Cardan, "changes of the Absides of the Planets cause mutations in governments and laws, which is a point very much to be regarded".