Earth

=== Size and shape ===
{{Main|Figure of the Earth}}
{{Further|Earth radius|Earth's circumference|Spherical Earth{{!}}Earth curvature|Geomorphology}}
{{See also|List of highest mountains on Earth}}
[[File:Earth2014shape SouthAmerica small.jpg|thumb|upright=1.3|Earth's western hemisphere showing topography relative to Earth's center instead of to [[mean sea level]], as in common topographic maps]]
[[Figure of the Earth|Earth has a rounded shape]], through [[hydrostatic equilibrium]],<ref name="Horner 2021">{{cite web | last=Horner | first=Jonti | title=I've always wondered: why are the stars, planets and moons round, when comets and asteroids aren't? | website=The Conversation | date=2021-07-16 | url=https://theconversation.com/amp/ive-always-wondered-why-are-the-stars-planets-and-moons-round-when-comets-and-asteroids-arent-160541 | access-date=2023-03-03}}</ref> with an average diameter of {{convert|12742|km|mi|sp=us}}, making it the [[List of Solar System objects by size|fifth largest]] [[Planet#Planetary-mass object|planetary sized]] and largest [[terrestrial planet|terrestrial object]] of the [[Solar System]].<ref>{{Cite web |last=Lea |first=Robert |date=2021-07-06 |title=How big is Earth? |url=https://www.space.com/17638-how-big-is-earth.html |archive-url=https://web.archive.org/web/20240109225632/https://www.space.com/17638-how-big-is-earth.html |archive-date=2024-01-09 |access-date=2024-01-11 |website=Space.com |language=en}}</ref>

Due to [[Earth's rotation]] it has the shape of an [[Earth ellipsoid|ellipsoid]], [[equatorial bulge|bulging at its Equator]]; its diameter is {{convert|43|km|mi|sp=us}} longer there than at its [[Geographical pole|poles]].<ref name="ngdc2006" /><ref name="milbert_smith96" />
Earth's shape furthermore has local [[topography|topographic]] variations. Though the largest local variations, like the [[Mariana Trench]] ({{convert|10925|m|ft|disp=or|abbr=|sp=us}} below local sea level),<ref>{{Cite journal|last1=Stewart|first1=Heather A.|last2=Jamieson|first2=Alan J.|date=2019|title=The five deeps: The location and depth of the deepest place in each of the world's oceans|journal=Earth-Science Reviews|language=en|volume=197|pages=102896|doi=10.1016/j.earscirev.2019.102896|bibcode=2019ESRv..19702896S|issn=0012-8252|doi-access=free}}</ref> only shortens Earth's average radius by 0.17% and [[Mount Everest]] ({{convert|8848|m|ft|disp=or|sp=us}} above local sea level) lengthens it by only 0.14%.{{refn|group=n| If Earth were shrunk to the size of a [[billiard ball]], some areas of Earth such as large mountain ranges and oceanic trenches would feel like tiny imperfections, whereas much of the planet, including the [[Great Plains]] and the [[abyssal plain]]s, would feel smoother.<ref>{{cite web |url=http://billiards.colostate.edu/bd_articles/2013/june13.pdf |title=Is a Pool Ball Smoother than the Earth? |publisher=Billiards Digest |date=1 June 2013 |access-date=26 November 2014}}</ref>}}<ref>{{cite web|url=https://serc.carleton.edu/quantskills/activities/botec_himalayas.html|title=Back-of-the-Envelope Calculations: Scale of the Himalayas|work=[[Carleton University]]|last1=Tewksbury|first1=Barbara|access-date=19 October 2020}}</ref> Since Earth's surface is farthest out from Earth's [[center of mass]] at its equatorial bulge, the summit of the volcano [[Chimborazo]] in Ecuador ({{Convert|6384.4|km|mi|1|abbr=on|disp=or}}) is its farthest point out.<ref name=ps20_5_16 /><ref>{{cite web |url=https://www.npr.org/templates/story/story.php?storyId=9428163 |title=The 'Highest' Spot on Earth |last1=Krulwich|first1=Robert|author-link=Robert Krulwich|work=NPR |date=7 April 2007 |access-date=31 July 2012}}</ref>
Parallel to the rigid land topography [[Ocean surface topography|the Ocean exhibits a more dynamic topography]].<ref>{{Cite web |title=Ocean Surface Topography |url=https://sealevel.jpl.nasa.gov/ocean-observation/ocean-surface-topography |access-date=16 June 2022 |website=Ocean Surface Topography from Space |publisher = NASA |language=en}}</ref>

To measure the local variation of Earth's topography, [[geodesy]] employs an idealized Earth producing a shape called a [[geoid]]. Such a geoid shape is gained if the ocean is idealized, covering Earth completely and without any perturbations such as tides and winds. The result is a smooth but gravitational irregular geoid surface, providing a mean sea level (MSL) as a reference level for topographic measurements.<ref>{{Cite web|title=What is the geoid?|url=https://oceanservice.noaa.gov/facts/geoid.html|access-date=10 October 2020|publisher=[[National Ocean Service]]|language=EN-US}}</ref>