Editing Prime meridian (section)

== History ==
{{See also|History of longitude}}

[[File:Ptolemy-World Vat Urb 82.jpg|right|thumb|upright=1.3|[[Ptolemy]]'s 1st projection, redrawn under [[Maximus Planudes]] around 1300, using a prime meridian through the [[Canary Islands]] west of Africa, at the left-hand edge of the map. (The obvious central line shown here is the junction of two sheets).]]

The notion of longitude for Greeks was developed by the [[Greeks|Greek]] [[Eratosthenes]] (c.{{nbsp}}276{{snd}}195{{nbsp}}BCE) in [[Alexandria]], and [[Hipparchus]] (c.{{nbsp}}190{{snd}}120{{nbsp}}BCE) in [[Rhodes]], and applied to a large number of cities by the [[geographer]] [[Strabo]] (64/63{{nbsp}}BCE{{snd}}c.{{nbsp}}24{{nbsp}}CE). [[Ptolemy]] (c.{{nbsp}}90{{snd}}168{{nbsp}}CE) was the first geographer to use a consistent meridian for a world map, in his ''[[Geography (Ptolemy)|Geographia]]''.

Ptolemy used as his basis the "[[Fortunate Isles]]", a group of islands in the [[Atlantic Ocean|Atlantic]], which are usually associated with the [[Canary Islands]] (13°W to 18°W), although his maps correspond more closely to the [[Cape Verde|Cape Verde islands]] (22°W to 25°W). The main point is to be comfortably west of the western tip of [[Africa]] (17°30′W) as negative numbers were not yet in use. His prime meridian corresponds to 18°40′ west of [[Winchester]] (about 20°W) today.{{sfn|Norgate|Norgate|2006}} At that time the chief method of determining longitude was by using the reported times of [[lunar eclipse]]s in different countries.

One of the earliest known descriptions of ''standard time'' in India appeared in the 4th century CE [[Hindu astronomy|astronomical]] treatise [[Surya Siddhanta]]. Postulating a [[spherical Earth]], the book described the thousands years old customs of the [[Prime Meridian|prime meridian]], or zero longitude, as passing through ''[[Avanti (India)|Avanti]]'', the ancient name for the historic city of [[Ujjain]], and ''Rohitaka'', the ancient name for [[Rohtak]] ({{Coord|28|54|N|76|38|E|type:city|name=Rohitaka (Rohtak)}}), a city near the [[Kurukshetra]].<ref>{{cite journal|last=Schmidt|first=Olaf H.|year=1944|title=The Computation of the Length of Daylight in Hindu Astronomy|url=https://www.jstor.org/stable/330729|url-status=live|archive-url=https://web.archive.org/web/20220126062053/https://www.jstor.org/stable/330729|archive-date=26 January 2022|access-date=|journal=Isis|volume=35|issue=3|pages=205–211|publisher=The University of Chicago Press|doi=10.1086/358709|jstor=330729|s2cid=145178197}}</ref>{{Better source needed|reason=Cited work discusses latitude not longitude.|date=July 2021}}

[[File:Propaganda Map.jpg|thumb|right|upright=1.4|[[William Griggs (inventor)|William Grigg]]'s facsimile of the 1529 [[Spanish Empire|Spanish]] [[Padron Real]], from the copy made by [[Diogo Ribeiro (cartographer)|Diogo Ribeiro]] and held by the [[Vatican Library]].]]
Ptolemy's ''Geographia'' was first printed with maps at [[Bologna]] in 1477, and many early globes in the 16th century followed his lead, but there was still a hope that a "natural" basis for a prime meridian existed. [[Christopher Columbus]] reported (1493) that the compass pointed due north somewhere in mid-Atlantic, and this fact was used in the important [[Treaty of Tordesillas]] of 1494, which settled the territorial dispute between [[Spain]] and [[Portugal]] over newly discovered lands. The Tordesillas line was eventually settled at 370 [[League (unit)|leagues]] (2,193 kilometers, 1,362 statute miles, or 1,184 nautical miles) west of [[Cape Verde]].{{efn| These figures use the ''legua náutica'' (nautical league) of four [[Roman mile]]s totalling {{convert|5.926|km|abbr=on}}, which was used by Spain during the 15th, 16th, and 17th centuries for navigation.<ref>{{cite journal |first=Roland |last=Chardon |title=The linear league in North America |journal=Annals of the Association of American Geographers |volume=70 |issue=2 |year=1980 |pages=129–153 [pp. 142, 144, 151] |jstor=2562946 |doi=10.1111/j.1467-8306.1980.tb01304.x}}</ref> In 1897 Henry Harrise noted that Jaime Ferrer, the expert consulted by King Ferdinand and Queen Isabella, stated that a league was four miles of six [[Stadion (unit of length)|stades]] each.<ref>{{cite book |first=Henry |last=Harrisse |url=https://books.google.com/books?id=7I4cAAAAMAAJ&pg=PA85  |title=The Diplomatic History of America: Its first chapter 1452—1493—1494 |location= London |publisher=Stevens |date=1897|pages=85–97, 176–190 |isbn=9780697000071 |oclc=1101220811}}</ref> Modern scholars agree that the geographic stade was the Roman or Italian stade, not any of several other Greek stades, supporting these figures.<ref>{{cite journal |first=Donald |last=Engels |title=The length of Eratosthenes' stade |journal=[[American Journal of Philology]] |volume=106 |issue=3 |year=1985 |pages=298–311 |jstor=295030 |doi=10.2307/295030}}</ref> Harrise is in the minority when he uses the stade of {{convert|192.27|m|abbr=on}} marked within the stadium at [[Olympia, Greece]], resulting in a league (32 stades) of {{convert|6.153|km|abbr=on}}, 3.8% larger.}} This is shown in the copies of Spain's [[Padron Real]] made by [[Diogo Ribeiro (cartographer)|Diogo Ribeiro]] in 1527 and 1529. [[São Miguel Island]] (25°30′W) in the [[Azores]] was still used for the same reason as late as 1594 by [[Christopher Saxton]], although by then it had been shown that the zero [[magnetic declination]] line did not follow a line of longitude.{{sfn|Hooker|2006}}

[[File:Atlas Ortelius KB PPN369376781-006av-006br.jpg|thumb|upright=1.3|1571 Africa map by [[Abraham Ortelius]], with [[Cape Verde]] as its prime meridian.]]
[[File:CEM-36-Regno-della-China-2355.jpg|thumb|upright=1.3|1682 map of East Asia by [[Giacomo Cantelli]], with Cape Verde as its prime meridian; [[Japan]] is thus located around 180° E.]]
In 1541, [[Gerardus Mercator|Mercator]] produced his 41&nbsp;cm terrestrial globe and drew his prime meridian precisely through [[Fuerteventura]] (14°1′W) in the Canaries. His later maps used the Azores, following the magnetic hypothesis, but by the time that [[Abraham Ortelius|Ortelius]] produced the first modern atlas in 1570, other islands such as Cape Verde were coming into use. In his atlas longitudes were counted from 0° to 360°, not 180°W to 180°E as is usual today. This practice was followed by navigators well into the 18th century.<ref>e.g. [[Jacob Roggeveen]] in 1722 reported the longitude of [[Easter Island]] as 268°45′ (starting from Fuerteventura) in the Extract from the Official log of Jacob Roggeveen reproduced in {{citation|title=The voyage of Don Felipe Gonzalez to Easter Island in 1770-1 |editor=Bolton Glanville Corney |date=1908 |page=3 |publisher=Hakluyt Society |url=https://archive.org/stream/voyagecaptaindo00unkngoog#page/n88/mode/2up |access-date=13 January 2013}}</ref> In 1634, [[Cardinal Richelieu]] used the westernmost island of the Canaries, [[El Hierro]], 19°55′ west of Paris, as the choice of meridian. The geographer [[Guillaume Delisle|Delisle]] decided to round this off to 20°, so that it simply became the meridian of Paris disguised.<ref>Speech by Pierre Janssen, director of the Paris observatory, at the first session of the [https://www.gutenberg.org/files/17759/17759-h/17759-h.htm#Page_73 Meridian Conference.] {{Webarchive|url=https://web.archive.org/web/20211218082731/https://www.gutenberg.org/files/17759/17759-h/17759-h.htm#Page_73 |date=18 December 2021 }}</ref>

In the early 18th century, the battle was on to improve the determination of longitude at sea, leading to the development of the [[marine chronometer]] by [[John Harrison]]. The development of accurate star charts, principally by the first British [[Astronomer Royal]], [[John Flamsteed]] between 1680 and 1719 and disseminated by his successor [[Edmund Halley]], enabled navigators to use the [[Lunar distance (navigation)|lunar method]] of determining longitude more accurately using the [[Octant (instrument)|octant]] developed by [[Thomas Godfrey (inventor)|Thomas Godfrey]] and [[John Hadley]].{{sfn|Sobel|Andrewes|1998|pp=110–115}}

In the 18th century most countries in [[Europe]] adapted their own ''prime'' meridian, usually through their capital, hence in [[France]] the [[Paris meridian]] was prime, in [[Kingdom of Prussia|Prussia]] it was the [[Berlin]] meridian, in [[Denmark]] the [[Copenhagen]] meridian, and in [[United Kingdom]] the [[Greenwich meridian]].

Between 1765 and 1811, [[Nevil Maskelyne]] published 49 issues of the [[The Nautical Almanac|''Nautical Almanac'']] based on the meridian of the [[Royal Observatory, Greenwich]]. "Maskelyne's tables not only made the lunar method practicable, they also made the [[Prime meridian (Greenwich)|Greenwich meridian]] the universal reference point. Even the French translations of the ''Nautical Almanac'' retained Maskelyne's calculations from Greenwich – in spite of the fact that every other table in the ''[[Connaissance des Temps]]'' considered the [[Paris meridian]] as the prime."{{sfn|Sobel|Andrewes|1998|pp=197–199}}

In 1884, at the [[International Meridian Conference]] in [[Washington, D.C.]], 22 countries voted to adopt the Greenwich meridian as the prime meridian of the world.<ref name="who decided">{{cite web |url=https://www.rmg.co.uk/stories/topics/what-prime-meridian-why-it-greenwich |title=What is the Prime Meridian - and why is it in Greenwich? {{!}} Who decided that the Prime Meridian should be in Greenwich? |publisher=Royal Museums Greenwich |date=n.d. |access-date=28 December 2021 |archive-date=5 January 2022 |archive-url=https://web.archive.org/web/20220105211313/https://www.rmg.co.uk/stories/topics/what-prime-meridian-why-it-greenwich |url-status=live }}</ref> The French argued for a neutral line, mentioning the Azores and the [[Bering Strait]], but eventually abstained and continued to use the [[Paris meridian]] until 1911.

The current international standard Prime Meridian is the [[IERS Reference Meridian]]. The  [[International Hydrographic Organization]] adopted an early version of the IRM in 1983 for all nautical charts.<ref>{{cite web |url= http://www.iho.shom.fr/publicat/free/files/S-51_Ed4-EN.pdf |title= A manual on the technical aspects of the United Nations Convention on the Law of the Sea – 1982 |access-date= 23 July 2008 |archive-date= 10 September 2008 |archive-url= https://web.archive.org/web/20080910223739/http://www.iho.shom.fr/publicat/free/files/S-51_Ed4-EN.pdf |url-status= live }}&nbsp;{{small|(4.89 MB)}} Section 2.4.4.</ref> It was adopted for air navigation by the [[International Civil Aviation Organization]] on 3 March 1989.<ref>[http://www.icao.int/pbn/docs/eurocontrolwgsman24.pdf WGS 84 Implementation Manual] {{Webarchive|url=https://web.archive.org/web/20081003102629/http://www.icao.int/pbn/docs/eurocontrolwgsman24.pdf |date=3 October 2008 }} page i, 1998</ref>