apsis

apsis

[ap-sis]
noun, plural apsides [ap-si-deez] .
1.
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.
2.
Architecture. an apse.

Origin:
1595–1605; < Latin < Greek hapsís (felloe of) a wheel, arch, vault, orig., fastening, equivalent to háp(tein) to fasten + -sis -sis

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World English Dictionary
apsis (ˈæpsɪs)
 
n , pl apsides
1.  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
2.  another name for apse
 
[C17: via Latin from Greek; see apse]
 
apsidal
 
adj

Collins English Dictionary - Complete & Unabridged 10th Edition
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Etymonline
Word Origin & History

apsis
"perigree of the moon, perihelion of a planet" (plural apsides), 1650s, from L. apsis "arch, vault" (see apse).
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Science Dictionary
apsis  [%PREMIUM_LINK%]     (āp'sĭs)  Pronunciation Key 
Plural apsides (āp'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.

The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Encyclopedia Britannica
Encyclopedia

apsis

in astronomy, either of the two points on an elliptical orbit that are nearest to, and farthest from, the focus, or centre of attraction. The line of apsides, connecting the two points, is the major axis of the orbit. The point nearest the focus is the pericentre, or periapsis, and that farthest from it is the apocentre, or apoapsis. Specific terms can be used for individual bodies: if the Sun is the centre, the specific terms perihelion and aphelion are generally used; if the Earth, perigee and apogee. Periastron and apastron refer to an orbit around a star, and perijove and apojove refer to an orbit around Jupiter

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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