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n. pl. ap·si·des (-sĭ-dēz′)
1. Architecture An apse.
2. Astronomy The point of greatest or least distance of the orbit of a celestial body from the center of mass of the system.

[Late Latin, from Latin, arch, vault, from Greek hapsis, from haptein, to fasten.]
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
References in periodicals archive ?
A generic AV-EGA maneuver can be labeled as K : L(M) [+ or -], where K and L indicate the number of revolutions that moon and probe complete, respectively, before the next encounter; M [less than or equal to] L denotes the spacecraft orbit where DSM occours; the sign [+ or -] is used to distinguish between the possible encounter locations: just before (-) or after (+) traversing the line of apsides.
The creeps and jitters in the orbital period may reveal mass loss and/or mass-swapping --both continuous and abrupt--or slow, one-way effects of stellar evolution, rotation of the line of apsides, or the orbital influence of unseen bodies.
Breiter [16] studies the third-body effects in the resonance of the apsides for satellites in low altitude, determining the resonant eccentricities between the secular motion of a satellite in terrestrial orbit and the longitudes of the Moon and the Sun.
Isimtimi bendroje simetriskoje kompozicijoje galima laikyti varpines boksta, kuris ikomponuotas ties baznycios kampu, salia apsides. Visai kitoks sprendimu budas pasirinktas kuriant Domeikavos Lietuvos Kankiniu baznycia (archit.: K.
Baznycios lubos--suformuotas cilindrinis skliautas (R 5,60 m), nedaug nuzemejantis apsides zonoje, is vidaus visas dengtas medinemis dailylentemis, visiskai paslepiant baznycios dvislaicio stogo konstrukcija.