Editing Earth radius (section)

==History==
{{See also|History of geodesy|Spherical Earth#History|Earth's circumference#History|Meridian arc#History}}

The first published reference to the Earth's size appeared around 350&nbsp;[[Anno Domini|BC]], when [[Aristotle]] reported in his book ''[[On the Heavens]]''<ref>{{cite book|last=Aristotle|author-link=Aristotle|title=On the Heavens|volume=Book II 298 B|url=http://classics.mit.edu/Aristotle/heavens.html|access-date=5 November 2017}}</ref> that mathematicians had guessed the circumference of the Earth to be 400,000 [[Stadia (length)|stadia]]. Scholars have interpreted Aristotle's figure to be anywhere from highly accurate<ref>
{{ cite journal
| journal = The Classical Journal
| title = On the Science of the Egyptians and Chaldeans, Part I
| volume = 16
| page = 159
| first = William
| last = Drummond
| year = 1817
}}</ref> to almost double the true value.<ref>
{{Cite EB1911|wstitle= Earth, Figure of the |volume= 8 |last1= Clarke |first1= Alexander Ross |author1-link= Alexander Ross Clarke |last2= Helmert |first2= Friedrich Robert |author2-link= Friedrich Robert Helmert | pages = 801&ndash;813 }}</ref> The first known scientific measurement and calculation of the circumference of the Earth was performed by [[Eratosthenes]] in about 240&nbsp;BC. Estimates of the error of Eratosthenes's measurement range from 0.5% to 17%.<ref>
{{cite encyclopedia
| encyclopedia = Britannica.com
| title = Eratosthenes, the Greek Scientist
| url = https://www.britannica.com/biography/Eratosthenes
| year = 2016
}}</ref> For both Aristotle and Eratosthenes, uncertainty in the accuracy of their estimates is due to modern uncertainty over which stadion length they meant.

Around 100&nbsp;BC, [[Posidonius of Apamea]] recomputed Earth's radius, and found it to be close to that by Eratosthenes,<ref>Posidonius, [http://www.attalus.org/translate/poseidonius.html#202.K fragment 202]</ref> but later [[Strabo]] incorrectly attributed him a value about 3/4 of the actual size.<ref>Cleomedes ([http://adsabs.harvard.edu/abs/1975QJRAS..16..152F in Fragment 202]) stated that if the distance is measured by some other number the result will be different, and using 3,750 instead of 5,000 produces this estimation: 3,750 x 48 = 180,000; see Fischer I., (1975), ''Another Look at Eratosthenes' and Posidonius' Determinations of the Earth's Circumference'', Ql. J. of the Royal Astron. Soc., Vol. 16, p. 152.</ref> [[Claudius Ptolemy]] around 150&nbsp;[[Anno Domini|AD]] gave empirical evidence supporting a [[spherical Earth]],<ref>{{Cite book|title=Early astronomy|last=Thurston|first=Hugh|publisher=Springer-Verlag New York|year=1994|isbn=0-387-94107-X|location=New York|page=138}}</ref> but he accepted the lesser value attributed to Posidonius. His highly influential work, the ''[[Almagest]]'',<ref>{{Cite web |title=Almagest – Ptolemy (Elizabeth) |url=https://projects.iq.harvard.edu/predictionx/almagest-ptolemy-elizabeth |access-date=2022-11-05 |website=projects.iq.harvard.edu |language=en}}</ref> left no doubt among medieval scholars that Earth is spherical, but they were wrong about its size.

By 1490, [[Christopher Columbus]] believed that traveling 3,000 miles west from the west coast of the [[Iberian Peninsula]] would let him reach the eastern coasts of [[Asia]].<ref>[[John Freely]], [https://books.google.com/books?id=MfhjAAAAQBAJ ''Before Galileo: The Birth of Modern Science in Medieval Europe''] (2013), {{ISBN|978-1468308501}}</ref> However, the 1492 enactment of that voyage [[Voyages of Christopher Columbus| brought his fleet to the Americas]]. The [[Magellan expedition]] (1519–1522), which was the first [[circumnavigation]] of the World, soundly demonstrated the sphericity of the Earth,<ref>{{Cite book|author=Nancy Smiler Levinson|title=Magellan and the First Voyage Around the World|url=https://books.google.com/books?id=1PbBzjBuW8IC&pg=PA39|access-date=31 July 2010|year=2001|publisher=Houghton Mifflin Harcourt|isbn=978-0-395-98773-5}}</ref> and affirmed the original measurement of {{convert|40000|km|mi|abbr=on}} by Eratosthenes.

Around 1690, [[Isaac Newton]] and [[Christiaan Huygens]] argued that Earth was closer to an [[Spheroid#Oblate spheroids | oblate spheroid]] than to a sphere. However, around 1730, [[Jacques Cassini]] argued for a [[Spheroid#Prolate spheroids | prolate spheroid]] instead, due to different interpretations of the [[Newtonian mechanics]] involved.<ref>{{cite book |last=Cassini |first=Jacques |title=Méthode de déterminer si la terre est sphérique ou non |date=1738 |url=https://bibnum.obspm.fr/items/show/41044#?c=0&m=0&s=0&cv=0&z=-0.0556%2C-0.339%2C1.1111%2C1.9323 |language=fr |access-date=2023-02-09 |archive-date=2018-01-27 |archive-url=https://web.archive.org/web/20180127004440/https://bibnum.obspm.fr/items/show/41044#?c=0&m=0&s=0&cv=0&z=-0.0556%2C-0.339%2C1.1111%2C1.9323 |url-status=dead }}</ref> To settle the matter, the [[French Geodesic Mission]] (1735–1739) measured one degree of [[latitude]] at two locations, one near the [[Arctic Circle]] and the other near the [[equator]]. The expedition found that Newton's conjecture was correct:<ref>{{Cite web|url=https://gallica.bnf.fr/ark:/12148/bpt6k5470853s|title=La Vie des sciences|last=Levallois|first=Jean-Jacques|date=1986|website=Gallica|pages=277–284, 288|access-date=2019-05-22}}</ref> the Earth is flattened at the [[Geographical pole|poles]] due to rotation's [[centrifugal force]].