[uh-fee-lee-uhn, uh-feel-yuhn, ap-hee-lee-uhn]
noun, plural aphelia [uh-fee-lee-uh, uh-feel-yuh, ap-hee-lee-uh] .
Astronomy. the point in the orbit of a planet or a comet at which it is farthest from the sun.
Compare perihelion.

1650–60; Hellenized form of Neo-Latin aphēlium < Greek *aphḗlion (diástēma) off-sun (distance), neuter of *aphḗlios (adj.), equivalent to ap- ap-2 + hḗli(os) sun + -os adj. suffix. See apogee

aphelian, adjective
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World English Dictionary
aphelion (æpˈhiːlɪən, əˈfiː-)
n , pl -lia
Compare perihelion the point in its orbit when a planet or comet is at its greatest distance from the sun
[C17: from New Latin aphēlium (with pseudo-Greek ending -ion) from ap- + Greek hēlios sun]

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

"point farthest from the sun" (of a celestial body's orbit), 1670s, from Mod.L. aphelium, the modern form an alteration by Johannes Kepler, based on Gk. apo heliou "away from the sun," from apo "away from" + heliou, gen. of helios "sun" (see sol). The whole was formed on the
model of Ptolemaic apogæum (see apogee) to reflect the new helio-centric model of the universe.
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Science Dictionary
aphelion  [%PREMIUM_LINK%]     (ə-fē'lē-ən)  Pronunciation Key 

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The point at which an orbiting body, such as a planet or comet, is farthest away from the Sun. Compare apogee, perihelion.

The American Heritage® Science Dictionary
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