Editing Christopher Columbus (section)

=== Geographical considerations ===
Despite [[Myth of the flat Earth|a popular misconception]] to the contrary, nearly all educated Westerners of Columbus's time knew that the [[Spherical Earth|Earth is spherical]], a concept that had been understood since [[Classical antiquity|antiquity]].{{sfn|Murphy|Coye|2013|p=244}} The techniques of [[celestial navigation]], which uses the position of the Sun and the stars in the sky, had long been in use by astronomers and were beginning to be implemented by mariners.<ref name="Willoz-Egnor2013">{{cite web |last1=Willoz-Egnor |first1=Jeanne |title=Mariner's Astrolabe |url=https://www.ion.org/museum/item_view.cfm?cid=6&scid=13&iid=25 |url-status=live |year=2013 |access-date=5 July 2021 |website=[[Institute of Navigation]] |archive-url=https://web.archive.org/web/20131029202740/http://www.ion.org/museum/item_view.cfm?cid=6&scid=13&iid=25 |archive-date=29 October 2013}}</ref><ref name="Smith2002">{{cite journal |last1=Smith |first1=Ben |title=An astrolabe from Passa Pau, Cape Verde Islands |journal=International Journal of Nautical Archaeology |date=1 January 2002 |volume=31 |issue=1 |pages=99–107 |doi=10.1006/ijna.2002.1021 |bibcode=2002IJNAr..31...99S |url=https://www.academia.edu/31744402}}</ref><!-- Please do not remove url just because the DOI is given; the webpage has a link to a free download, and the very good paper can be read right there. -->

However, Columbus made several errors in calculating the size of the Earth, the distance the continent extended to the east, and therefore the distance to the west to reach his goal.

First, as far back as the 3rd century&nbsp;BC, [[Eratosthenes]] had correctly computed the circumference of the Earth by using simple geometry and studying the shadows cast by objects at two remote locations.<ref>{{cite book |title=The Illustrated Encyclopedia of the Universe |last=Ridpath |first=Ian |publisher=Watson-Guptill |year=2001 |isbn=978-0-8230-2512-1 |location=New York |page=31}}</ref><ref>{{cite book |first=Carl |last=Sagan |author-link=Carl Sagan |title=Cosmos |publisher=[[Random House]] |url=https://archive.org/details/cosmossaga00saga/page/14/mode/2up?q=Eratosthenes |location=New York |year=1980 |isbn=978-0-394-50294-6 |pages=34–35 |access-date=20 February 2022 |url-access=registration}}</ref> In the 1st century&nbsp;BC, [[Posidonius]] confirmed Eratosthenes's results by comparing stellar observations at two separate locations. These measurements were widely known among scholars, but Ptolemy's use of the smaller, old-fashioned units of distance led Columbus to underestimate the size of the Earth by about a third.<ref name="Freely2013">{{cite book |last=Freely |first=John |url=https://books.google.com/books?id=QsWSDwAAQBAJ&pg=PT36 |title=Before Galileo: The Birth of Modern Science in Medieval Europe |publisher=[[Abrams Books]] |location=New York |year=2013 |isbn=978-1-4683-0850-1 |page=36}}</ref>

[[File:ColombusMap.jpg|thumb|upright=1.6|"Columbus map", drawn c.&nbsp;1490 in the [[Lisbon]] mapmaking workshop of Bartholomew and Christopher Columbus<ref>"Marco Polo et le Livre des Merveilles", p. 37. {{ISBN|978-2-35404-007-9}}</ref>]]

Second, three [[cosmographical]] parameters determined the bounds of Columbus's enterprise: the distance across the ocean between Europe and Asia, which depended on the extent of the [[oikumene]], i.e., the Eurasian land-mass stretching east–west between Spain and China; the circumference of the Earth; and the number of miles or [[League (unit)|leagues]] in a degree of [[longitude]], which was possible to deduce from the theory of the relationship between the size of the surfaces of water and the land as held by the followers of [[Aristotle]] in medieval times.<ref name="Randles1990">{{cite journal |last1=Randles |first1=W. G. L. |title=The Evaluation of Columbus' 'India' Project by Portuguese and Spanish Cosmographers in the Light of the Geographical Science of the Period |journal=Imago Mundi |date=January 1990 |volume=42 |issue=1 |page=50 |doi=10.1080/03085699008592691 |s2cid=129588714 |url=http://www.tau.ac.il/~corry/teaching/histint/download/Randles_Columbus.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.tau.ac.il/~corry/teaching/histint/download/Randles_Columbus.pdf |archive-date=9 October 2022 |url-status=live |issn=0308-5694}}</ref>

From [[Pierre d'Ailly]]'s ''{{lang|la|[[Imago Mundi (Pierre d'Ailly)|Imago Mundi]]}}'' (1410), Columbus learned of [[Alfraganus]]'s estimate that a degree of [[latitude]] (equal to approximately a degree of [[longitude]] along the equator) spanned 56.67&nbsp;[[Arabic mile]]s (equivalent to {{convert|66.2|nmi|km|1|abbr=off|sp=us|disp=comma}} or 76.2&nbsp;mi), but he did not realize that this was expressed in the Arabic mile (about {{Convert|1,830|m|mi|abbr=out|sp=us|disp=or}}) rather than the shorter [[Roman mile]] (about 1,480&nbsp;m) with which he was familiar.<ref name="Mahmud2017">{{cite journal |last1=Khairunnahar |last2=Mahmud |first2=Khandakar Hasan |last3=Islam |first3=Md Ariful |title=Error calculation of the selected maps used in the Great Voyage of Christopher Columbus |journal=The Jahangirnagar Review, Part II |year=2017 |volume=XLI |page=67 |url=https://www.researchgate.net/publication/348442261 |access-date=9 January 2022 |publisher=Jahangirnagar University |issn=1682-7422}}</ref> Columbus therefore estimated the size of the Earth to be about 75% of Eratosthenes's calculation.<ref name="McCormick2012">{{cite web |last1=McCormick |first1=Douglas |title=Columbus's Geographical Miscalculations |url=https://spectrum.ieee.org/columbuss-geographical-miscalculations |website=IEEE Spectrum |access-date=9 January 2022 |date=9 October 2012}}</ref>

Third, most scholars of the time accepted Ptolemy's estimate that [[Eurasia]] spanned 180° longitude,<ref name="Gunn2018">{{cite book |last1=Gunn |first1=Geoffrey C. |title=Overcoming Ptolemy: The Revelation of an Asian World Region |date=2018 |publisher=Rowman & Littlefield |isbn=978-1-4985-9014-3 |pages=77–78 |url=https://books.google.com/books?id=xCRyDwAAQBAJ&pg=PA77 |quote=Constructed on a framework of latitude and longitude, the Ptolemy-revival map projections revealed the extent of the known world in relation to the whole. Typically, they displayed a Eurasian landmass extending through 180° of longitude from a prime meridian in the west (variously the Canary Islands or Cape Verde) to a location in the "Far East."}}</ref> rather than the actual 130° (to the Chinese mainland) or 150° (to Japan at the latitude of Spain). Columbus believed an even higher estimate, leaving a smaller percentage for water.<ref name="Zacher2016">{{cite book |last1=Zacher |first1=Christian K. |editor1-last=Bedini |editor1-first=Silvio A. |title=The Christopher Columbus Encyclopedia |year=2016 |publisher=Springer |isbn=978-1-349-12573-9 |pages=676–677 |url=https://books.google.com/books?id=gmmMCwAAQBAJ&pg=PA676}}</ref> In d'Ailly's ''{{lang|la|Imago Mundi}}'', Columbus read [[Marinus of Tyre]]'s estimate that the longitudinal span of Eurasia was 225° at the latitude of [[Rhodes]].<ref name="Dilke2016">{{cite book |last1=Dilke |first1=O. A. W. |editor1-last=Bedini |editor1-first=Silvio A. |title=The Christopher Columbus Encyclopedia |year=2016 |publisher=Springer |isbn=978-1-349-12573-9 |page=452 |chapter-url=https://books.google.com/books?id=gmmMCwAAQBAJ&pg=PA452 |chapter=Marinus of Tyre}}</ref> Some historians, such as [[Samuel Eliot  Morison]], have suggested that he followed the statement in the [[Biblical apocrypha|apocryphal]] book [[2 Esdras]] ([[:wikisource:Bible (King James)/II Esdras#Chapter 6|6:42]]) that "six parts [of the globe] are habitable and the seventh is covered with water."<ref name="Morison1974">{{cite book |last1=Morison |first1=Samuel Eliot |title=The European Discovery of America: The Southern Voyages A.D. 1492–1616 |date=1974 |publisher=Oxford University Press |isbn=978-0-19-501377-1 |page=31 |url=https://books.google.com/books?id=r4sOAQAAMAAJ&q=%222%20Esdras%22}}</ref> He was also aware of Marco Polo's claim that Japan (which he called "Cipangu") was some {{Convert|2414|km|mi|abbr=on}} to the east of China ("Cathay"),<ref name="Butel2002">{{cite book |last1=Butel |first1=Paul |title=The Atlantic |year=2002 |publisher=Routledge |isbn=978-1-134-84305-3 |page=47 |url=https://books.google.com/books?id=sLGIAgAAQBAJ&pg=PA47}}</ref> and closer to the equator than it is. He was influenced by Toscanelli's idea that there were inhabited islands even farther to the east than Japan, including the mythical [[Antillia]], which he thought might lie not much farther to the west than the [[Azores]],{{sfn|Morison|1991|p=}} and the distance westward from the [[Canary Islands]] to the Indies as only 68 degrees, equivalent to {{Convert|3080|nmi|abbr=on}} (a 58% error).<ref name="McCormick2012" />

Based on his sources, Columbus estimated a distance of {{convert|2,400|nmi|abbr=on}} from the Canary Islands west to Japan; the actual distance is {{convert|10600|nmi|abbr=on}}.{{sfn|Phillips|Phillips|1992|p=110}}<ref name="Edson2007">{{cite book |last1=Edson |first1=Evelyn |title=The World Map, 1300–1492: The Persistence of Tradition and Transformation |year=2007 |publisher=JHU Press |isbn=978-0-8018-8589-1 |page=205 |url=https://books.google.com/books?id=dhgYlhXJy_QC&pg=PA205}}</ref> No ship in the 15th century could have carried enough food and fresh water for such a long voyage,<ref name="Taylor2002">{{cite book |last1=Taylor |first1=Alan |title=American Colonies: The Settling of North America (The Penguin History of the United States, Volume 1) |year=2002 |publisher=Penguin |isbn=978-0-14-200210-0 |page=34 |url=https://books.google.com/books?id=NPoAQRgkrOcC&pg=PA34}}</ref> and the dangers involved in navigating through the uncharted ocean would have been formidable. Most European navigators reasonably concluded that a westward voyage from Europe to Asia was unfeasible. The Catholic Monarchs, however, having completed the {{lang|es|[[Reconquista]]}}, an expensive war against the [[Moors]] in the [[Iberian Peninsula]], were eager to obtain a competitive edge over other European countries in the quest for trade with the Indies. Columbus's project, though far-fetched, held the promise of such an advantage.<ref>{{cite book |first=De Lamar |last=Jensen |date=1992 |title=Renaissance Europe |publisher=[[D.C. Heath and Company]] |location=Lexington, Massachusetts |edition=2nd |isbn=978-0-669-20007-2 |page=341}}</ref>
[[File:Christopher Columbus at the gates of the monastery of Santa Maria de la Rabida with his son Diego (cropped).jpg|thumb|upright=0.8|''Christopher Columbus at the gates of the monastery of Santa María de la Rábida with his son [[Diego Columbus|Diego]]'', by [[Benet Mercadé]]]]