aph·​elion | \ a-ˈfēl-yən How to pronounce aphelion (audio) , ˌap-ˈhēl- How to pronounce aphelion (audio) \
plural aphelia\ a-​ˈfēl-​yə How to pronounce aphelia (audio) , ˌap-​ˈhēl-​ \

Definition of aphelion

: the point farthest from the sun in the path of an orbiting celestial body (such as a planet) — compare perihelion

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Did You Know?

Aphelion and perihelion are troublesome terms. Which one means a planet is nearest to the sun and which means it is farthest away? An etymology lesson may help you keep those words straight. Just remember that the "ap" of aphelion derives from a Latin prefix that means "away from" (the mnemonic "'A' for 'away'" can help too); peri-, on the other hand, means "near." And how are aphelion and perihelion related to the similar-looking astronomical pair, apogee and perigee? Etymology explains again. The "helion" of aphelion and perihelion is based on the Greek word hēlios, meaning "sun," while the "gee" of apogee and perigee is based on gaia, meaning "earth." The first pair describes distance in relation to the sun, the second in relation to the earth.

Examples of aphelion in a Sentence

Recent Examples on the Web The closest of these run-ins occurs when Earth reaches aphelion, or its farthest point from the sun, and when Mars reaches perihelion, its closest point to the sun. Jennifer Leman, Popular Mechanics, "How to Get an Absolutely Perfect View of Mars This Week," 5 Oct. 2020 Apart from Mercury, no other natural object in our solar system is known to have a smaller aphelion—the point at which an orbiting body is farthest from the sun. Katherine J. Wu, Smithsonian Magazine, "Astronomers Spot First Asteroid Nearer to the Sun Than Venus," 21 Jan. 2020 Mars’ orbit is more elliptical than Earth’s, so the difference between perihelion and aphelion is greater. Dave Epstein, BostonGlobe.com, "Mars is going to be really bright for the rest of the summer," 11 July 2018 Over the past centuries, Mars’ orbit has been getting more and more elongated, carrying the planet even nearer to the sun at perihelion and even farther away at aphelion. Dave Epstein, BostonGlobe.com, "Mars is going to be really bright for the rest of the summer," 11 July 2018 Image On Friday, Earth will swing toward the outermost point in its orbit, known as aphelion. Shannon Hall, New York Times, "Never Mind the Summer Heat: Earth Is at Its Greatest Distance From the Sun," 5 July 2018 After orbiting the Earth for 6 hours, a third-stage burn-to-depletion was completed at approximately 02:30 UTC Feb 7, placing the dummy payload in a heliocentric orbit having a perihelion of 0.99 au and aphelion ~1.7 au. Joe Pappalardo, Popular Mechanics, "We Know Exactly Where Musk’s Space Tesla Is Going," 8 Feb. 2018 Confirming the rocket firing, SpaceX released initial data indicating the Roadster was headed for an elliptical orbit around the sun with a high point, or aphelion, out in the asteroid belt, well beyond the orbit of Mars. William Harwood, CBS News, ""Starman" and Tesla heading for deep space," 7 Feb. 2018 Each year, during wintertime in the northern hemisphere, the Earth reaches its closest point to the sun, or perihelion, and during the northern hemisphere summer the Earth hits the farthest point from the sun, or aphelion. Jay Bennett, Popular Mechanics, "One Day There Will Be No More Total Solar Eclipses," 18 Aug. 2017

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'aphelion.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of aphelion

1656, in the meaning defined above

History and Etymology for aphelion

New Latin, from apo- + Greek hēlios sun — more at solar

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Time Traveler for aphelion

Time Traveler

The first known use of aphelion was in 1656

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Last Updated

13 Oct 2020

Cite this Entry

“Aphelion.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/aphelion. Accessed 29 Nov. 2020.

More from Merriam-Webster on aphelion

Britannica.com: Encyclopedia article about aphelion

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