See APHELION, APOGEE, PERIHELION, and PERIGEE.
The Apsides are also called Apogees. See APOGEE. The Diameter which joins these two Points is called the Line of the Apsides, and passes through the Center of the Orbit of the Planet, and the Center of the Earth,—which is the Line AP, (Tab. Astronomy, fig. 1.) drawn from the Aphelion A to the Perihelion P.
See ORBIT and PLANET.
The Eccentricity is reckoned in the Line of the Apsides: being the Distance between the Center of the Orbit of the Planet C, and the Center of the Sun or Earth S, according as the Copernican or the Ptolemaic System is followed. See ECCENTRICITY. For the Motion of the Line of the Apsides, see Apogee, etc. The Word comes from the Greek ἀψίς (apsis), an Arch, or Vault.
Apsides were also anciently used for a kind of private Oratories, or Chapels in great Churches; otherwise called Doxologia, or Doxalia. See ORATORY. They were thus called, because arched or vaulted over. The Word still obtains in the Low Countries, where it denotes a kind of Choir, or Place beyond the Altar; where the Religious sit, and sing the Office, separate from the People, and without being seen by them.