from The American Heritage® Dictionary of the English Language, 5th Edition.

  • noun The point on the orbit of a celestial body that is farthest from the sun.

from The Century Dictionary.

  • noun That point of a planet's or of a comet's orbit which is most distant from the sun: opposed to perihelion.

from the GNU version of the Collaborative International Dictionary of English.

  • noun (Astron.) That point of a planet's or comet's orbit which is most distant from the sun, the opposite point being the perihelion.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

  • noun astronomy The point in the elliptical orbit of a planet, comet, etc., where it is farthest from the sun.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • noun apoapsis in solar orbit; the point in the orbit of a planet or comet that is at the greatest distance from the sun


from The American Heritage® Dictionary of the English Language, 4th Edition

[From New Latin aphēlium : Greek apo-, apo- + Greek hēlios, sun; see sāwel- in Indo-European roots.]

from Wiktionary, Creative Commons Attribution/Share-Alike License

Greek form of Latin aphelium, from Ancient Greek ἀπό (apo, "from") + ἥλιος (hēlios, "sun") (modelled after apogaeum). Compare perihelion.


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  • In order for this result to be produced, the earth must reach that part of its orbit known as aphelion, where the distance from its controlling centre is greatest, so that the eccentricity of the moon's orbit is always an indication of the position of the earth in its relation to the sun.

    Aether and Gravitation William George Hooper

  • At the opposite point of its orbit, where it will be in "aphelion," or farthest from the sun, the sun will only appear about 19 minutes in diameter.

    To Mars via The Moon An Astronomical Story Mark Wicks

  • The first colonists arrived only to learn that they had to contend with a winter twenty times the duration of summer and so extreme it froze the atmosphere to the surface well after aphelion to the primary.

    Mandala « A Fly in Amber 2010

  • Criminy, I almost forgot: on July 4th, at roughly 08: 00 UT, the Earth was at aphelion.

    Does the Sun Look Smaller to You? | Disinformation 2008

  • So whether or not Pluto is moving towards perihelion or aphelion that doesn't determine its "spring" or "autumn", does it?

    New Hubble Images Show Pluto is Changing | Universe Today 2010

  • Comets, with their hugely eccentric orbits, may pass far beyond the outer planets to spend their aphelion in the vast interstellar darkness beyond the Kuiper Belt . » artnouveauho: Aphelion 2010

  • When the orbit is more elliptical, the perihelion is closer to the Sun and the aphelion is farther away than when the orbit is more circular.

    Milankovitch cycles 2009

  • Scotsman James Croll combined the eccentricity of the orbit and the precession and in the 1860s and 1870s presented his ideas on the effects of the cycles and how they might influence climate, especially the colder winters when they correspond with the aphelion.

    Milankovitch cycles 2009

  • Figure 1: Position of the equinoxes, solstices, aphelion, and perihelion on the Earth's orbit.

    Earth-Sun geometry 2009

  • In 12,900 years, the North will have colder winters because Earth will be furthest from the Sun (aphelion) in January.

    Milankovitch cycles 2009


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  • Surprisingly, this word is pronounced properly "a-phelion" instead of the common "ap-helion", as in Greek the pi + rough breathing elides to phi. Granted, in the more ancient pronunciation phi *is in fact pronounced as an aspirated pi, but that approaches pedantry. For comparison see ephemeral.

    September 19, 2008

  • "... in astronomy, is that part of a planet's orbit which is at the greatest distance from the sun, being that end of the greater axis of the elliptic orbit of the planet, most remote from the focus wherein the sun is placed; and is, therefore, opposed to Perihelion.

    "The times of the aphelia of the primary planets may be known by their apparent diameter appearing the smallest, and also by their moving with the least velocity, in a given time. They may likewise be found by calculation, which De Lande, De la Caille, and other astronomical writers treat of at large."

    Falconer's New Universal Dictionary of the Marine (1816), 19

    October 13, 2008