Perihelion and aphelion - wikipedia Perihelion and aphelion This is the current revision of this page, as edited by Geoffrey. landis ( talk contribs ) at 18 : 06, 28 July 2017 ( rephrased cause of deviation from ellipse ). The present address ( URL ) is a permanent link to this version. Revision as of 18 : 06, 28 July 2017 by Geoffrey. landis ( talk contribs ) ( rephrased cause of deviation from ellipse ) ( diff ) ← Previous revision Latest revision ( diff ) Newer revision → ( diff ) This article is about astronomy. For the image analysis software suite, see Aphelion ( software ). For other uses, see Aphelion ( disambiguation ). For a more general treatment of the subject, see Apsis. The perihelion and aphelion are the nearest and farthest points ( apsides ) of a body 's direct orbit around the Sun. The perihelion is the point in the orbit of a celestial body where it is nearest to its orbital focus, generally a star. It is the opposite of aphelion, which is the point in the orbit where the celestial body is farthest from its focus. The word `` perihelion '' stems from the Ancient Greek words `` peri '', meaning `` around '' or `` surrounding '', and `` helios '', meaning `` the Sun ''. `` Aphelion '' derives from the preposition `` apo '', meaning `` away, off, apart ''. ( The similar words `` perigee '' and `` apogee '' refer to the nearest and furthest points in some object 's orbit around the Earth. ) According to Kepler 's first law of planetary motion, all planets, comets, and asteroids in the Solar System have approximately elliptical orbits around the Sun. ( It is only approximate because of perturbations due to the gravity of other bodies. ) Hence, an orbiting body has a closest and a farthest point from its parent object, that is, a perihelion and an aphelion. Each extreme is known as an apsis. Orbital eccentricity measures the flatness ( departure from a perfect circle ) of the orbit. Contents 1 Etymology 2 Application to Earth 3 See also 4 References 5 External links Etymology The words perihelion and aphelion were coined by Johannes Kepler to describe the orbital motion of the planets. The words are formed from the prefixes peri - ( Greek : περί, near ) and apo - ( Greek : ἀπό, away from ) affixed to the Greek word for the sun, ήλιος. Application to Earth Earth is about 147.1 million kilometers ( 91.4 million miles ) from the Sun at perihelion around January 3, in contrast to about 152.1 million kilometers ( 94.5 million miles ) at aphelion around July 4 -- a difference of about 5.0 million kilometers ( 3.1 million miles ). ( These dates change over time due to precession and other orbital factors, which follow cyclical patterns known as Milankovitch cycles. For a table of these dates for various years, see Apsis. ) Because of the increased distance at aphelion, only 93.55 % of the solar radiation from the Sun falls on a given area of land as does at perihelion. However, this fluctuation does not account for the seasons, as it is summer in the northern hemisphere when it is winter in the southern hemisphere and vice versa. Instead, seasons result from the tilt of Earth 's axis, which is 23.4 degrees away from perpendicular to the plane of Earth 's orbit around the sun. Winter falls on the hemisphere where sunlight strikes least directly, and summer falls where sunlight strikes most directly, regardless of the Earth 's distance from the Sun. In the northern hemisphere, summer occurs at the same time as aphelion. Despite this, there are larger land masses in the northern hemisphere, which are easier to heat than the seas. Consequently, summers are 2.3 ° C ( 4 ° F ) warmer in the northern hemisphere than in the southern hemisphere under similar conditions. See also Astronomy portal Solar System portal Apsis Ellipse Solstice References Jump up ^ `` Perihelion and Aphelion ''. National Earth Science Teachers Association ( NESTA ). Retrieved 2015 - 09 - 19. Jump up ^ `` Introductory Astronomy : Ellipses ''. Washington State University. Jump up ^ Klein, Ernest, A Comprehensive Etymological Dictionary of the English Language, Elsevier, Amsterdam, 1965. ( Archived version ) Jump up ^ Since the Sun, Ἥλιος in Greek, begins with a vowel ( H is considered a vowel in Greek ), the final o in `` apo '' is omitted from the prefix. The pronunciation `` Ap - helion '' is given in many dictionaries ( 1 ), pronouncing the `` p '' and `` h '' in separate syllables. However, the pronunciation / əˈfiːliən / ( 2 ) is also common ( e.g., McGraw Hill Dictionary of Scientific and Technical Terms, 5th edition, 1994, p. 114 ), since in late Greek, ' p ' from ἀπό followed by the ' h ' from ἥλιος becomes phi ; thus, the Greek word is αφήλιον. ( see, for example, Walker, John, A Key to the Classical Pronunciation of Greek, Latin, and Scripture Proper Names, Townsend Young 1859 ( 3 ), page 26. ) Many ( 4 ) dictionaries give both pronunciations Jump up ^ `` Solar System Exploration : Science & Technology : Science Features : Weather, Weather, Everywhere ? ''. NASA. Retrieved 2015 - 09 - 19. Jump up ^ `` Earth at Aphelion ''. Space Weather. July 2008. Retrieved 7 July 2015. External links Dates and times of Earth 's perihelion and aphelion, 2000 -- 2025 from the United States Naval Observatory Retrieved from `` https://en.wikipedia.org/w/index.php?title=Perihelion_and_aphelion&oldid=792790411 '' Categories : Orbits Stars Planets Minor planets Comets Talk Article Talk More Contents About Wikipedia Bân - lâm - gú فارسی हिन्दी עברית Scots සිංහල اردو Edit links This page was last edited on 28 July 2017, at 18 : 06. Text is available under the Creative Commons Attribution - ShareAlike License ; additional terms may apply. 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Question: the point at which a planet is the greatest distance away from the sun
Answer: aphelion