- See under apsis.
noun, plural ap·si·des [ap-si-deez] /ˈæp sɪˌdiz/.
- Astronomy. either of two points in an eccentric orbit, one (higher apsis) farthest from the center of attraction, the other (lower apsis) nearest to the center of attraction.
- Architecture. an apse.
noun plural apsides (æpˈsaɪdiːz, ˈæpsɪˌdiːz)
- Also called: apse either of two points lying at the extremities of an eccentric orbit of a planet, satellite, etc, such as the aphelion and perihelion of a planet or the apogee and perigee of the moon. The line of apsides connects two such points and is the principal axis of the orbit
- another name for apse (def. 1)
“perigree of the moon, perihelion of a planet” (plural apsides), 1650s, from Latin apsis “arch, vault” (see apse).
Plural apsides (ăp′sĭ-dēz′)
- In the path of an orbiting body, either of the two points at which it is closest to or farthest away from the body it is orbiting. See also apoapsis periapsis.