[per-uh-hee-lee-uhn, -heel-yuhn]
noun, plural perihelia [per-uh-hee-lee-uh, -heel-yuh] . Astronomy.
the point in the orbit of a planet or comet at which it is nearest to the sun.
Compare aphelion.

1660–70; < Greek peri- peri- + hḗli(os) sun + -on neuter noun suffix, on the model of perigee; earlier in the Neo-Latin form perihelium

perihelial, perihelian, adjective Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
perihelion (ˌpɛrɪˈhiːlɪən)
n , pl -lia
Compare aphelion the point in its orbit when a planet or comet is nearest the sun
[C17: from New Latin perihēlium, from peri- + Greek hēlios sun]

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

"point at which a celestial body is nearest the Sun," 1690, coined in Mod.L. (perihelium) by Kepler (1596) from Gk. peri "near" + helios "sun" (see sol), and subsequently re-Grecianized.
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Science Dictionary
perihelion  [%PREMIUM_LINK%]     (pěr'ə-hē'lē-ən)  Pronunciation Key 

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The point at which an orbiting object, such as a planet or a comet, is closest to the Sun. Compare aphelion, perigee.

The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Example sentences
The radius of perihelion can be varied to allow for faster flight times to the target.
The comet is on its way out of the inner solar system, having made perihelion last spring.
Images for perihelion
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