[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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Based on the Random House Dictionary, © Random House, Inc. 2014.
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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
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Example sentences
What it says is that the neighborhood is what goes from perihelion to aphelion.
The presence of these was originally inferred by looking at the aphelion of short and long period comets respectively.
Images for aphelion
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