Editing Prime meridian

{{Short description|Line of longitude, at which longitude is defined to be 0°}}
{{Redirect|Prime Meridian|Earth's prime meridian, often called the Prime Meridian|IERS Reference Meridian|the historical meridian it is based on|Prime meridian (Greenwich)}}
{{Use dmy dates|date=September 2019}}
{{Location map-line|lon=0|caption=Modern [[IERS Reference Meridian]] on Earth}}

A '''prime meridian''' is an arbitrarily chosen<!--This does not mean "on a whim", it means that there is no geodesic basis for it, as there is for the equator. Perhaps comparison with prime meridian of Mars may make the point clearer? --> [[meridian (geography)|meridian]] (a line of [[longitude]]) in a [[geographic coordinate system]] at which longitude is defined to be 0°. On a spheroid, a prime meridian and its anti-meridian (the [[180th meridian]] in a [[degree (angle)|360°-system]]) form a [[great ellipse]]. This divides the body (e.g. [[Earth]]) into [[hemispheres of Earth|two hemispheres]]: the [[Eastern Hemisphere]] and the [[Western Hemisphere]] (for an east-west notational system). For Earth's prime meridian, various conventions have been used or advocated in different regions throughout history.{{sfn|Norgate|Norgate|2006}} Earth's current [[international standard]] prime meridian is the [[IERS Reference Meridian]]. It is derived, but differs slightly, from the [[Prime meridian (Greenwich)|Greenwich Meridian]], the previous standard.<ref>{{cite web |title=What is the Prime Meridian and why is it in Greenwich? |url=https://www.rmg.co.uk/stories/topics/what-prime-meridian-why-it-greenwich |website=Royal Museums Greeenwich |access-date=13 December 2021 |quote=The IRM is the only meridian that may now be described as the prime meridian of the world, as it defines 0° longitude by international agreement. The IRM passes 102.5 metres (112 yards) to the east of the historic Prime Meridian of the World at the latitude of the Airy Transit Circle here. The entire Observatory and the historic Prime Meridian now lie to the west of the true prime meridian. |archive-date=13 December 2021 |archive-url=https://web.archive.org/web/20211213045150/https://www.rmg.co.uk/stories/topics/what-prime-meridian-why-it-greenwich |url-status=live }}</ref>

[[File:Atlas Cosmographicae (Mercator) 033.jpg|thumb|upright=1.3|right|[[Gerardus Mercator]] in his ''[[Atlas Cosmographicae]]'' (1595) used a prime meridian somewhere close to [[25th meridian west|25°W]], passing just to the west of [[Santa Maria Island]] in the [[Azores]] in the [[Atlantic Ocean]]. His 180th meridian runs along the [[Strait of Anián]] (Bering Strait)]]

Longitudes for the Earth and [[Moon]] are measured from their prime meridian (at 0°) to 180° east and west. For all other [[Solar System]] bodies, longitude is measured from 0° (their prime meridian) to 360°. West longitudes are used if the rotation of the body is [[Retrograde and prograde motion|prograde]] (or 'direct', like Earth), meaning that its direction of rotation is the same as that of its orbit. East longitudes are used if the rotation is [[Retrograde and prograde motion|retrograde]].<ref name=cartographic>{{citation |last=Archimal |first=B. A. |title=Report of the IAU Working Group on Cartographic Coordinates and Rotational Elements: 2015 |url=https://astropedia.astrogeology.usgs.gov/download/Docs/WGCCRE/WGCCRE2015reprint.pdf |year=2015 |page=27 of 46 |quote=[W]est longitudes are used when the rotation is direct, and east longitudes are used when the rotation is retrograde. ... The Earth, Sun, and Moon do not traditionally conform to this definition. Their rotations are direct and longitudes run both east and west 180°, or positive to the east 360°. [footnotes omitted] |access-date=6 August 2019 |archive-date=6 August 2019 |archive-url=https://web.archive.org/web/20190806225003/https://astropedia.astrogeology.usgs.gov/download/Docs/WGCCRE/WGCCRE2015reprint.pdf |url-status=live }}</ref>

== 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>

==International prime meridian==
Since 1984, the international standard for the  Earth's prime meridian is the IERS Reference Meridian. Between 1884 and 1984, the meridian of Greenwich was the world standard. These meridians are very close to each other.

===Prime meridian at Greenwich{{anchor|Greenwich}}===
[[File:Prime meridian.jpg|thumb|upright=1.2|The line of the [[Prime meridian (Greenwich)|Greenwich meridian]] at the [[Royal Observatory, Greenwich]], England]]
{{Main|Prime meridian (Greenwich)}}
In October 1884 the Greenwich Meridian was selected by delegates (forty-one delegates representing twenty-five nations) to the [[International Meridian Conference]] held in [[Washington, D.C.]], [[United States]] to be the common zero of longitude and standard of time reckoning throughout the world.<ref name=imc>{{cite book|title=International Conference Held at Washington for the Purpose of Fixing a Prime Meridian and a Universal Day. October, 1884. Protocols of the proceedings|url=https://www.gutenberg.org/files/17759/17759-h/17759-h.htm|publisher=Project Gutenberg|access-date=30 November 2012|date=1884|archive-date=18 December 2021|archive-url=https://web.archive.org/web/20211218082731/https://www.gutenberg.org/files/17759/17759-h/17759-h.htm|url-status=live}}</ref>{{efn|Voting took place on 13 October and the resolutions were adopted on 22 October 1884.<ref>{{harvnb|Howse|1997|pp=12, 137}}</ref> The modern prime meridian, the IERS Reference Meridian, is placed very near this meridian.<ref name="who decided" />}}

The position of the historic prime meridian, based at the [[Royal Observatory, Greenwich]], was established by [[George Biddell Airy|Sir George Airy]] in 1851. It was defined by the location of the [[Meridian circle#19th century|Airy Transit Circle]] ever since the first observation he took with it.<ref name="Greenwich Observatory p.10">{{cite book  |title=Greenwich Observatory ... the story of Britain's oldest scientific institution, the Royal Observatory at Greenwich and Herstmonceux, 1675–1975 |volume=1  |first=Eric Gray |last=Forbes |page=10 |publisher=Taylor & Francis |date=1975 |isbn=9780850660937}}</ref> Prior to that, it was defined by a succession of earlier transit instruments, the first of which was acquired by the second [[Astronomer Royal]], [[Edmond Halley]] in 1721. It was set up in the extreme north-west corner of the Observatory between Flamsteed House and the Western Summer House. This spot, now subsumed into Flamsteed House, is roughly 43 metres (47 yards) to the west of the Airy Transit Circle, a distance equivalent to roughly 2 seconds of longitude.{{sfn|Dolan|2013a}} It was Airy's transit circle that was adopted in principle (with French delegates, who pressed for adoption of the [[Paris meridian]] abstaining) as the Prime Meridian of the world at the 1884 International Meridian Conference.<ref name="Time">{{cite book|
title=TIME from Earth Rotation to Atomic Physics
|last1=McCarthy
|first1=Dennis
|author-link1=Dennis McCarthy (scientist)
|last2=Seidelmann
|first2=P. Kenneth
|pages=244–5
|location=Weinheim
|publisher=Wiley-VCH
|date=2009}}</ref><ref name="RMG">{{cite web|url= http://www.rmg.co.uk/explore/astronomy-and-time/astronomy-facts/history/the-prime-meridian-at-greenwich|title= The Prime Meridian at Greenwich|author= ROG Learning Team|date= 23 August 2002|work= Royal Museums Greenwich|access-date= 14 June 2012|archive-date= 7 November 2015|archive-url= https://web.archive.org/web/20151107023957/http://www.rmg.co.uk/explore/astronomy-and-time/astronomy-facts/history/the-prime-meridian-at-greenwich|url-status= live}}</ref>

All of these Greenwich meridians were located via an astronomic observation from the surface of the Earth, oriented via a [[plumb line]] along the direction of gravity at the surface. This astronomic Greenwich meridian was disseminated around the world, first via the [[lunar distance method]], then by chronometers carried on ships, then via telegraph lines carried by [[submarine communications cable]]s, then via radio time signals. One remote longitude ultimately based on the Greenwich meridian using these methods was that of the [[North American Datum#North American Datum of 1927|North American Datum 1927]] or NAD27, an ellipsoid whose surface best matches [[mean sea level]] under the [[United States]].

===IERS Reference Meridian===
{{Main|IERS Reference Meridian}}

Beginning in 1973 the [[International Time Bureau]] and later the [[International Earth Rotation and Reference Systems Service]] changed from reliance on optical instruments like the Airy Transit Circle to techniques such as [[Lunar Laser Ranging experiment|lunar laser ranging]], [[satellite laser ranging]], and [[very-long-baseline interferometry]]. The new techniques resulted in the IERS Reference Meridian, the plane of which passes through the centre of mass of the Earth. This differs from the plane established by the Airy transit, which is affected by [[vertical deflection]] (the local vertical is affected by influences such as nearby mountains).  The change from relying on the local vertical to using a meridian based on the centre of the Earth caused the modern prime meridian to be [[Minute and second of arc#Symbols and abbreviations|5.3{{pprime}}]] east of the astronomic Greenwich prime meridian through the Airy Transit Circle. At the latitude of Greenwich, this amounts to 102 metres (112 yards).<ref>{{cite journal| title = Why the Greenwich meridian moved | first1 = Stephen | last1 = Malys | first2 = John H. | last2 = Seago | first3 = Nikolaos K. | last3 = Palvis | first4 = P. Kenneth | last4 = Seidelmann | first5 = George H. | last5 = Kaplan | journal = Journal of Geodesy | volume = 89 | issue = 12 | pages = 1263 | date = 1 August 2015 | doi = 10.1007/s00190-015-0844-y|bibcode = 2015JGeod..89.1263M | doi-access = free }}</ref> This was officially accepted by the [[Bureau International de l'Heure]] (BIH) in 1984 via its BTS84 (BIH Terrestrial System) that later became WGS84 (World Geodetic System 1984) and the various [[International Terrestrial Reference Frame]]s (ITRFs).

Due to the movement of Earth's [[Plate tectonics|tectonic plates]], the line of 0° longitude along the surface of the Earth has slowly moved toward the west from this shifted position by a few centimetres (inches); that is, towards the Airy Transit Circle (or the Airy Transit Circle has moved toward the east, depending on your point of view) since 1984 (or the 1960s). With the introduction of satellite technology, it became possible to create a more accurate and detailed global map. With these advances there also arose the necessity to define a reference meridian that, whilst being derived from the Airy Transit Circle, would also take into account the effects of plate movement and variations in the way that the Earth was spinning.{{sfn|Dolan|2013b}}
As a result, the [[IERS Reference Meridian]] was established and is commonly used to [[Denotation (semiotics)|denote]] the Earth's prime meridian (0° longitude) by the [[International Earth Rotation and Reference Systems Service]], which defines and maintains the link between longitude and time. Based on observations to satellites and celestial compact radio sources (quasars) from various coordinated stations around the globe, Airy's [[transit circle]] drifts northeast about 2.5 centimetres (1 inch) per year relative to this Earth-centred 0° longitude.

It is also the reference meridian of the [[Global Positioning System]] operated by the [[United States Department of Defense]], and of [[WGS84]] and its two formal versions, the ideal [[International Terrestrial Reference System]] (ITRS) and its realization, the [[International Terrestrial Reference Frame]] (ITRF).<ref name="GPS">{{Cite web|url=http://gpsinformation.net/main/greenwich.htm|title=Greenwich Meridan, Tracing its History|website=gpsinformation.net|access-date=29 November 2006|archive-date=19 December 2017|archive-url=https://web.archive.org/web/20171219193541/http://www.gpsinformation.net/main/greenwich.htm|url-status=live}}</ref><ref name="IRM">[http://www.gearthblog.com/images/images2006/primemeridian.jpg IRM on grounds of Royal Observatory from Google Earth] {{Webarchive|url=https://web.archive.org/web/20161014021413/http://www.gearthblog.com/images/images2006/primemeridian.jpg |date=14 October 2016 }} Accessed 30 March 2012</ref>{{efn|The astronomic latitude of the Royal Observatory is 51°28{{prime}}38{{pprime}}N whereas its latitude on the European Terrestrial Reference Frame (1989) [[datum (geodesy)|datum]] is 51°28{{prime}}40.1247{{pprime}}N.}} A current convention on the Earth uses the line of longitude 180° opposite the IRM as the basis for the [[International Date Line]].

====List of places====
{{geoGroup}}
On Earth, starting at the [[North Pole]] and heading south to the [[South Pole]], the IERS Reference Meridian (as of 2016) passes through 8 countries, 4 seas, 3 oceans and 1 channel:

[[File:Meridian-International.svg|thumb|The prime meridian on a globe]]
[[File:Panneau du méridien de Greenwich à Parnay .jpg|thumb|The prime meridian sign in [[Parnay, Maine-et-Loire]], France.]]
[[File:Prime Meridian Line, Longitude 0.jpg|thumb|Prime meridian sign near [[Somanya]], Ghana.]]
{| class="wikitable plainrowheaders"
! scope="col" width="125" | Co-ordinates<br />(approximate)
! scope="col" | Country, territory or sea
! scope="col" | Notes
|- 
| style="background:#b0e0e6;" | {{Coord|90|0|N|0|0|E|type:waterbody|name=North Pole}}
! scope="row" style="background:#b0e0e6;" | [[North Pole]] and [[Arctic Ocean]]
| style="background:#b0e0e6;" |
|- 
| style="background:#b0e0e6;" | {{Coord|85|46|N|0|0|E|type:waterbody|name=EEZ of Greenland (Denmark)}}
! scope="row" style="background:#b0e0e6;" | [[EEZ|Exclusive Economic Zone (EEZ)]] of [[Greenland]] ([[Danish Realm|Denmark]])
| style="background:#b0e0e6;" |
|- 
| style="background:#b0e0e6;" | {{Coord|81|39|N|0|0|E|type:waterbody|name=Greenland Sea}}
! scope="row" style="background:#b0e0e6;" | [[Greenland Sea]]
| style="background:#b0e0e6;" |
|- 
| style="background:#b0e0e6;" | {{Coord|80|29|N|0|0|E|type:waterbody|name=EEZ of Svalbard (Norway)}}
! scope="row" style="background:#b0e0e6;" | [[EEZ]] of [[Svalbard]] ([[Norway]])
| style="background:#b0e0e6;" |
|- 
| style="background:#b0e0e6;" | {{Coord|76|11|N|0|0|E|type:waterbody|name=International waters}}
! scope="row" style="background:#b0e0e6;" | [[International waters]]
| style="background:#b0e0e6;" |
|- 
| style="background:#b0e0e6;" | {{Coord|73|44|N|0|0|E|type:waterbody|name=EEZ of Jan Mayen}}
! scope="row" style="background:#b0e0e6;" | [[EEZ]] of [[Jan Mayen]] ([[Norway]])
| style="background:#b0e0e6;" |
|- 
| style="background:#b0e0e6;" | {{Coord|72|53|N|0|0|E|type:waterbody|name=Norwegian Sea}}
! scope="row" style="background:#b0e0e6;" | [[Norwegian Sea]]
| style="background:#b0e0e6;" |
|- 
| style="background:#b0e0e6;" | {{Coord|69|7|N|0|0|E|type:waterbody|name=International waters}}
! scope="row" style="background:#b0e0e6;" | [[International waters]]
| style="background:#b0e0e6;" |
|- 
| style="background:#b0e0e6;" | {{Coord|64|42|N|0|0|E|type:waterbody|name=EEZ of Norway}}
! scope="row" style="background:#b0e0e6;" | [[EEZ]] of [[Norway]]
| style="background:#b0e0e6;" |
|- 
| style="background:#b0e0e6;" | {{Coord|63|29|N|0|0|E|type:waterbody|name=EEZ of Great Britain}}
! scope="row" style="background:#b0e0e6;" | [[EEZ]] of [[Great Britain]]
| style="background:#b0e0e6;" |
|-
| style="background:#b0e0e6;" | {{Coord|61|0|N|0|0|E|type:waterbody|name=North Sea}}
! scope="row" style="background:#b0e0e6;" | [[North Sea]]
| style="background:#b0e0e6;" |
|- 
| {{Coord|53|46|N|0|0|E|type:country|name=United Kingdom}}
! scope="row" | {{UK}}
| From [[Tunstall, East Riding of Yorkshire|Tunstall in East Riding]] to [[Peacehaven]], passing through [[Greenwich]]
|- 
| style="background:#b0e0e6;" | {{Coord|50|47|N|0|0|E|type:waterbody|name=English Channel}}
! scope="row" style="background:#b0e0e6;" | [[English Channel]]
| style="background:#b0e0e6;" | [[EEZ]] of Great Britain
|- 
| style="background:#b0e0e6;" | {{Coord|50|14|N|0|0|E|type:waterbody|name=EEZ of France}}
! scope="row" style="background:#b0e0e6;" | [[English Channel]]
| style="background:#b0e0e6;" | [[EEZ]] of [[France]]
|- 
| {{Coord|49|20|N|0|0|E|type:country|name=France}}
! scope="row" | {{FRA}}
| From [[Villers-sur-Mer]] to [[Gavarnie]]
|- 
| {{Coord|42|41|N|0|0|E|type:country|name=Spain}}
! scope="row" | {{ESP}}
| From [[Cilindro de Marboré]] to [[Castellón de la Plana]]
|- 
| style="background:#b0e0e6;" | {{Coord|39|56|N|0|0|E|type:waterbody|name=Mediterranean Sea}}
! scope="row" style="background:#b0e0e6;" | [[Mediterranean Sea]]
| style="background:#b0e0e6;" | [[Gulf of Valencia]]; [[EEZ]] of [[Spain]]
|- 
| {{Coord|38|52|N|0|0|E|type:country|name=Spain}}
! scope="row" | {{ESP}}
| From [[El Verger]] to [[Calp]]
|- 
| style="background:#b0e0e6;" | {{Coord|38|38|N|0|0|E|type:waterbody|name=Mediterranean Sea}}
! scope="row" style="background:#b0e0e6;" | [[Mediterranean Sea]]
| style="background:#b0e0e6;" | [[EEZ]] of [[Spain]]
|- 
| style="background:#b0e0e6;" | {{Coord|37|1|N|0|0|E|type:waterbody|name=EEZ of Algeria}}
! scope="row" style="background:#b0e0e6;" | [[Mediterranean Sea]]
| style="background:#b0e0e6;" | [[EEZ]] of [[Algeria]]
|- 
| {{Coord|35|50|N|0|0|E|type:country|name=Algeria}}
! scope="row" | {{DZA}}
|From [[Stidia]] to Algeria-Mali border near [[Bordj Badji Mokhtar]]
|- 
| {{Coord|21|52|N|0|0|E|type:country|name=Mali}}
! scope="row" | {{MLI}}
| Passing through [[Gao]]
|- 
| {{Coord|15|00|N|0|0|E|type:country|name=Burkina Faso}}
! scope="row" | {{BFA}}
| For about {{Convert|432|km|abbr=on}}, running through [[Cinkassé]].
|- 
| {{Coord|11|7|N|0|0|E|type:country|name=Togo}}
! scope="row" | {{TOG}}
| For about {{Convert|3.4|km|abbr=on}}
|- 
| {{Coord|11|6|N|0|0|E|type:country|name=Ghana}}
! scope="row" | {{GHA}}
| For about {{Convert|16|km|4=0|abbr=on}}
|- 
| {{Coord|10|58|N|0|0|E|type:country|name=Togo}}
! scope="row" | {{TOG}}
| For about {{Convert|39|km|abbr=on}}
|- 
| {{Coord|10|37|N|0|0|E|type:country|name=Ghana}}
! scope="row" | {{GHA}}
| From the Togo-Ghana border near [[Bunkpurugu]] to [[Tema]]<br>Passing through [[Lake Volta]] at {{coord|7|46|N|0|0|E|type:waterbody_region:GH|name=Lake Volta}}
|- 
| style="background:#b0e0e6;" | {{Coord|5|37|N|0|0|E|type:waterbody|name=EEZ of Ghana in Atlantic Ocean}}
! scope="row" style="background:#b0e0e6;" rowspan="5" | [[Atlantic Ocean]]
| style="background:#b0e0e6;" | [[EEZ]] of [[Ghana]]
|- 
| style="background:#b0e0e6;" | {{Coord|1|58|N|0|0|E|type:waterbody|name=International waters}}
! scope="row" style="background:#b0e0e6;" | [[International waters]]
|- 
| style="background:#b0e0e6;" | {{Coord|0|0|N|0|0|E|type:landmark|name=Equator}}
| scope="row" style="background:#b0e0e6;" | Passing through the [[Equator]] (see [[Null Island]])
|- 
| style="background:#b0e0e6;" | {{Coord|51|43|S|0|0|E|type:waterbody|name=EEZ of Bouvet Island}}
! scope="row" style="background:#b0e0e6;" | [[EEZ]] of [[Bouvet Island]] ([[Norway]])
|- 
| style="background:#b0e0e6;" | {{Coord|57|13|S|0|0|E|type:waterbody|name=International waters}}
! scope="row" style="background:#b0e0e6;" | [[International waters]]
|- 
| style="background:#b0e0e6;" | {{Coord|60|0|S|0|0|E|type:waterbody|name=Southern Ocean}}
! scope="row" style="background:#b0e0e6;" | [[Southern Ocean]]
! scope="row" style="background:#b0e0e6;" | [[International waters]]
|- 
| {{Coord|69|36|S|0|0|E|type:country|name=Antarctica}}
! scope="row" | [[Antarctica]]
| [[Queen Maud Land]], [[List of Antarctic territorial claims|claimed]] by {{NOR}}
|- 
| {{Coord|90|0|S|0|0|E|type:city|name=Amundsen–Scott South Pole Station}}
! scope="row" | [[Antarctica]]
| [[Amundsen–Scott South Pole Station]], [[South Pole]]
|- 
|}

==Prime meridian on other celestial bodies{{anchor|Planets}}==
{{See also|Longitude (planets)}}
{{Redirect-distinguish|Prime meridian (planets)|Central meridian (planets)}}

As on the Earth, prime meridians must be arbitrarily defined. Often a landmark such as a crater is used; other times a prime meridian is defined by reference to another celestial object, or by [[magnetic fields]]. 
The prime meridians of the following planetographic systems have been defined:

* Two different [[Solar coordinate systems#Heliographic|heliographic coordinate systems]] are used on the Sun. The first is the Carrington heliographic coordinate system. In this system, the prime meridian passes through the center of the solar disk as seen from the Earth on 9 November 1853, which is when the English astronomer [[Richard Christopher Carrington]] started his observations of [[sunspots]].<ref>{{Cite web|url=http://www.encyclopedia.com/doc/1O80-Carringtonheligrphccrdnts.html|title=Carrington heliographic coordinates|access-date=27 July 2009|archive-date=28 June 2011|archive-url=https://web.archive.org/web/20110628232407/http://www.encyclopedia.com/doc/1O80-Carringtonheligrphccrdnts.html|url-status=live}}</ref> The second is the [[Stonyhurst Observatory#Stonyhurst heliographic coordinates|Stonyhurst heliographic coordinates]] system, originated at [[Stonyhurst Observatory]] in [[Lancashire]], England.
* In 1975 the prime meridian of [[Mercury (planet)|Mercury]] was defined<ref>[[Merton E. Davies]], "Surface Coordinates and Cartography of Mercury," Journal of Geophysical Research, Vol. 80, No. 17, 10 June 1975</ref><ref>[[Merton E. Davies]], S. E. Dwornik, D. E. Gault, and R. G. Strom, NASA Atlas of Mercury, NASA Scientific and Technical Information Office, 1978.</ref> to be 20° east of the crater [[Hun Kal (crater)|Hun Kal]].<ref name="IAU09">{{Cite journal
| doi = 10.1007/s10569-010-9320-4
| title = Report of the IAU Working Group on Cartographic Coordinates and Rotational Elements: 2009
| url = http://astropedia.astrogeology.usgs.gov/alfresco/d/d/workspace/SpacesStore/28fd9e81-1964-44d6-a58b-fbbf61e64e15/WGCCRE2009reprint.pdf <!--
| url = http://astropedia.astrogeology.usgs.gov/download/Docs/WGCCRE/WGCCRE2009reprint.pdf -->
| journal = Celestial Mechanics and Dynamical Astronomy
| volume = 109
| issue = 2
| pages = 101–135
| year = 2010
| last1 = Archinal
| first1 = Brent A.
| last2 = A'Hearn
| first2 = Michael F.
| last3 = Bowell
| first3 = Edward G.
| last4 = Conrad
| first4 = Albert R.
| last5 = Consolmagno
| first5 = Guy J.
| display-authors = 5
| last6 = Courtin
| first6 = Régis
| last7 = Fukushima
| first7 = Toshio
| last8 = Hestroffer
| first8 = Daniel
| last9 = Hilton
| first9 = James L.
| last10 = Krasinsky
| first10 = George A.
| last11 = Neumann
| first11 = Gregory A.
| last12 = Oberst
| first12 = Jürgen
| last13 = Seidelmann
| first13 = P. Kenneth
| last14 = Stooke
| first14 = Philip J.
| last15 = Tholen
| first15 = David J.
| last16 = Thomas
| first16 = Paul C.
| last17 = Williams
| first17 = Iwan P.
| bibcode = 2011CeMDA.109..101A
| s2cid = 189842666
| access-date = 26 September 2018
| archive-url = https://web.archive.org/web/20160304065344/http://astropedia.astrogeology.usgs.gov/alfresco/d/d/workspace/SpacesStore/28fd9e81-1964-44d6-a58b-fbbf61e64e15/WGCCRE2009reprint.pdf
| archive-date = 4 March 2016
| url-status = dead
}}</ref> This meridian was chosen because it runs through the point on Mercury's equator where the average temperature is highest (due to the planet's rotation and orbit, the sun briefly [[Apparent retrograde motion|retrogrades]] at noon at this point during [[perihelion]], giving it more sunlight).<ref>Davies, M. E., "Surface Coordinates and Cartography of Mercury," Journal of Geophysical Research, Vol. 80, No. 17, June 10, 1975.</ref><ref name="ArchinalA’Hearn2010">{{cite journal |last1=Archinal |first1=Brent A. |display-authors=4 |last2=A'Hearn |first2=Michael F. |last3=Bowell |first3=Edward L. |last4=Conrad |first4=Albert R. |last5=Consolmagno |first5=Guy J. |last6=Courtin |first6=Régis |last7=Fukushima |first7=Toshio |last8=Hestroffer |first8=Daniel |last9=Hilton |first9=James L. |last10=Krasinsky |first10=George A. |last11=Neumann |first11=Gregory A. |last12=Oberst |first12=Jürgen |last13=Seidelmann |first13=P. Kenneth |last14=Stooke |first14=Philip J. |last15=Tholen |first15=David J. |last16=Thomas |first16=Peter C. |last17=Williams |first17=Iwan P. |title=Report of the IAU Working Group on Cartographic Coordinates and Rotational Elements: 2009 |journal=Celestial Mechanics and Dynamical Astronomy |volume=109 |issue=2 |date=2010 |pages=101–135 |issn=0923-2958 |doi=10.1007/s10569-010-9320-4 |bibcode=2011CeMDA.109..101A|s2cid=189842666 }}</ref><ref name="usgs">{{cite web |url=https://astrogeology.usgs.gov/Projects/WGCCRE/constants/iau2000_table1.html |access-date=October 22, 2009 |title=USGS Astrogeology: Rotation and pole position for the Sun and planets (IAU WGCCRE) |archive-url=https://web.archive.org/web/20111024101856/http://astrogeology.usgs.gov/Projects/WGCCRE/constants/iau2000_table1.html |archive-date=October 24, 2011 |url-status=dead}}</ref>
* Defined in 1992,<ref>[[Merton E. Davies]]; Colvin, T. R.; Rogers, P. G.; Chodas, P. G.; Sjogren, W. L.; Akim, W. L.; Stepanyantz, E. L.; Vlasova, Z. P.; and Zakharov, A. I.; "The Rotation Period, Direction of the North Pole, and Geodetic Control Network of Venus", ''Journal of Geophysical Research'', vol. 97, no. 8, 1992, pp. 1–14, 151</ref> the prime meridian of [[Venus]] passes through the central peak in [[Ariadne (crater)|the crater Ariadne]], chosen arbitrarily.<ref>{{cite web |url=https://astrogeology.usgs.gov/Projects/WGCCRE/constants/iau2000_table1.html |access-date=22 October 2009 |title=USGS Astrogeology: Rotation and pole position for the Sun and planets (IAU WGCCRE) |archive-url=https://web.archive.org/web/20111024101856/http://astrogeology.usgs.gov/Projects/WGCCRE/constants/iau2000_table1.html |archive-date=24 October 2011 |url-status=dead }}</ref>
* The prime meridian of the [[Moon]] lies directly in the middle of the face of the Moon visible from Earth and passes near the crater [[Bruce (crater)|Bruce]].{{cn|date=March 2025}}
* The prime meridian of [[Mars]] was established in 1971<ref>[[Merton E. Davies]], and Berg, R. A.; "Preliminary Control Net of Mars", ''Journal of Geophysical Research'', vol. 76, no. 2, 10 January 1971, pp. 373–393</ref> and passes through the center of the crater [[Airy-0]], although it is fixed by the longitude of the [[Viking 1#Lander|''Viking 1'' lander]], which is defined to be 47.95137°W.<ref>{{ Citation | last1 = Archinal | first1 = Brent A. | last2 = Acton  | first2 = C. H. | last3 = A'Hearn | first3 = Michael F. | author3-link = Michael A'Hearn | last4 = Conrad | first4 = Albert R.  |display-authors=etal| date = 2018 | title = Report of the IAU Working Group on Cartographic Coordinates and Rotational Elements: 2015 | journal = Celestial Mechanics and Dynamical Astronomy | volume = 130 | issue = 22 | pages = 22 | doi = 10.1007/s10569-017-9805-5 | bibcode = 2018CeMDA.130...22A | s2cid = 189844155 }}</ref>
*The prime meridian on [[Ceres (dwarf planet)|Ceres]] runs through the Kait crater, which was arbitrarily chosen because it is near the equator (about 2° south).<ref>{{cite web|title= New Maps of Ceres Reveal Topography Surrounding Mysterious 'Bright Spots'|author= Marc Reyman|publisher=NASA|date=30 October 2015|url=https://www.jpl.nasa.gov/blog/2015/10/new-maps-of-ceres-reveal-topography-surrounding-mysterious-bright-spots|accessdate=13 September 2022}}</ref>
*The prime meridian on [[4 Vesta]] is 4 degrees east of the crater [[Claudia (crater)|Claudia]], chosen because it is sharply defined.<ref name=IAUcoordinates>{{cite web|url=https://astrogeology.usgs.gov/search/details/Docs/WGCCRE/IAU-WGCCRE-Coordinate-System-for-Vesta/pdf |title=IAU WGCCRE Coordinate System for Vesta {{pipe}} USGS Astrogeology Science Center |publisher=Astrogeology.usgs.gov |date=2013-11-15 |access-date=2014-06-25}}</ref>
*[[Jupiter]] has several coordinate systems because its cloud tops—the only part of the planet visible from space—rotate at different rates depending on latitude.<ref>{{cite web |url=https://reference.wolfram.com/legacy/applications/astronomer/AdditionalInformation/PlanetographicCoordinates.html |title=Planetographic Coordinates |access-date=24 May 2017 |archive-date=15 April 2012 |archive-url=https://web.archive.org/web/20120415120251/http://reference.wolfram.com/legacy/applications/astronomer/AdditionalInformation/PlanetographicCoordinates.html |url-status=live }}</ref> It is unknown whether Jupiter has any internal solid surface that would enable a more Earth-like coordinate system. System I and System II coordinates are based on atmospheric rotation, and System III coordinates use Jupiter's magnetic field. The prime meridians of Jupiter's four [[Galilean moons]] were established in 1979.<ref>[[Merton E. Davies]], Thomas A. Hauge, et al.: Control Networks for the Galilean Satellites: November 1979 R-2532-JPL/NASA</ref>
**[[Europa (moon)|Europa]]'s prime meridian is defined such that [[Cilix (crater)|the crater Cilix]] is at 182° W.<ref name="IAU09"/> The 0° longitude runs through the middle of the face that is always turned towards Jupiter.
**[[Io (moon)|Io]]'s prime meridian, like that of Earth's moon, is defined so that it runs through the middle of the face that is always turned towards Jupiter (the near side, known as the subjovian hemisphere).<ref name="Lopes2005">{{cite journal |title=Io after ''Galileo'' |journal=[[Reports on Progress in Physics]] |last1=Lopes |first1=R. M. C. |author1-link=Rosaly Lopes |first2=D. A. |last2=Williams |pages=303–340 |volume=68 |issue=2 |date=2005 |doi=10.1088/0034-4885/68/2/R02 |bibcode=2005RPPh...68..303L|s2cid=44208045 }}</ref>
**[[Ganymede (moon)|Ganymede]]'s prime meridian is defined such that [[Anat (crater)|the crater Anat]] is at 128° W, and the 0° longitude runs through the middle of the subjovian hemisphere.<ref name="iau.table2">{{cite web |url=https://astrogeology.usgs.gov/Projects/WGCCRE/constants/iau2000_table2.html |title=USGS Astrogeology: Rotation and pole position for planetary satellites (IAU WGCCRE) |access-date=August 28, 2017 |archive-url=https://web.archive.org/web/20111024101848/http://astrogeology.usgs.gov/Projects/WGCCRE/constants/iau2000_table2.html |archive-date=October 24, 2011 |url-status=dead }}</ref>
**[[Callisto (moon)|Callisto]]'s prime meridian is defined such that [[Saga (crater)|the crater Saga]] is at 326° W.<ref>''Satellites of Jupiter''.&nbsp;(1982:912).&nbsp;United States:&nbsp;University of Arizona Press.</ref>
*[[Titan (moon)|Titan]] is the largest moon of [[Saturn]] and, like the Earth's moon, is tidally locked and always has the same face towards Saturn. The middle of that face is 0 longitude.{{cn|date=March 2025}}
*Like Jupiter, [[Neptune]] is a gas giant, so any surface is obscured by clouds. The prime meridian of its largest moon, [[Triton (moon)|Triton]], was established in 1991.<ref>[[Merton E. Davies]], P. G. Rogers, and T. R. Colvin, "A Control Network of Triton," Journal of Geophysical Research, Vo l. 96, E l, pp. 15,675-15,681, 1991.</ref>
*[[Pluto]]'s prime meridian is defined as the meridian passing through the center of the face that is always towards [[Charon (moon)|Charon]], its largest moon, as the two are tidally locked to each other. Charon's prime meridian is similarly defined as the meridian always facing directly toward Pluto.

==List of historic prime meridians on Earth==

{| class="wikitable"
|-
! Locality
! Modern longitude
! style="width:200px;"| Meridian name
!Image
! Comment
|-
| [[Bering Strait]] || 168°30′ W
|
|{{Location map-line|lon=-168}}
| Offered in 1884 as possibility for a neutral prime meridian by [[Pierre Janssen]] at the International Meridian Conference<ref>[https://www.gutenberg.org/files/17759/17759-h/17759-h.htm International Conference Held at Washington for the Purpose of Fixing a Prime Meridian and a Universal Day. October, 1884] {{Webarchive|url=https://web.archive.org/web/20211218082731/https://www.gutenberg.org/files/17759/17759-h/17759-h.htm |date=18 December 2021 }}, pp. 43&ndash;51. Project Gutenberg</ref>
|- 
| rowspan="4" | [[Washington, D.C.]] || 77°03{{prime}}56.07{{pprime}} W (1897) or 77°04{{prime}}02.24{{pprime}} W (NAD 27){{clarify|date=December 2016}} or 77°04{{prime}}01.16{{pprime}} W (NAD 83)
| [[New Naval Observatory meridian]]
| rowspan="4" |{{Location map-line|lon=-77}}
|
|-
|  77°02{{prime}}48.0{{pprime}} W, 77°03{{prime}}02.3{{pprime}}, 77°03{{prime}}06.119{{pprime}} W or 77°03{{prime}}06.276{{pprime}} W (both presumably NAD 27). If NAD27, the latter would be 77°03{{prime}}05.194{{pprime}} W (NAD 83)
| [[Old Naval Observatory meridian]]
|
|-
| 77°02{{prime}}11.56299{{pprime}} W (NAD 83),{{sfn|NGS|2016|loc = PID: HV1847}} 77°02{{prime}}11.55811{{pprime}} W (NAD 83),{{sfn|NGS|2016|loc = PID: HV1846}} 77°02{{prime}}11.58325{{pprime}} W (NAD 83){{sfn|NGS|2016|loc = PID: AH7372}} (three different monuments originally intended to be on the White House meridian)
| [[White House meridian]]
|
|-
| 77°00{{prime}}32.6{{pprime}} W (NAD 83)
| [[Capitol meridian]]
|
|-
| [[Philadelphia, Pennsylvania|Philadelphia]] || 75° 10{{prime}} 12{{pprime}} W 
|
|{{Location map-line|lon=-75}}
|{{sfn|Hooker|2006|loc=introduction}}<ref name="WIRED">[https://www.wired.com/2010/10/1013greenwich-prime-meridian/ Oct. 13, 1884: Greenwich Resolves Subprime Meridian Crisis] {{Webarchive|url=https://web.archive.org/web/20181201141846/https://www.wired.com/2010/10/1013greenwich-prime-meridian/ |date=1 December 2018 }}, ''WIRED'', 13 October 2010.</ref>
|- 
| [[Rio de Janeiro]] || 43° 10{{prime}} 19{{pprime}} W 
|
|{{Location map-line|lon=-43}}
|<ref>[http://www.maproom.org/00/49/index.php Atlas do Brazil] {{Webarchive|url=https://web.archive.org/web/20140616011924/http://www.maproom.org/00/49/index.php |date=16 June 2014 }}, 1909, by Barão Homem de Mello e Francisco Homem de Mello, published in Rio de Janeiro by F. Briguiet & Cia.</ref>
|-
| [[Fortunate Isles]] / Azores || 25° 40{{prime}} 32{{pprime}} W
|
|{{Location map-line|lon=-25}}
| Used until the Middle Ages, proposed as one possible neutral meridian by [[Pierre Janssen]] at the International Meridian Conference<ref name="gutenberg.org">{{cite web |url=https://www.gutenberg.org/files/17759/17759-h/17759-h.htm |title=The Project Gutenberg eBook of International Conference Held at Washington for the Purpose of Fixing a Prime Meridian and a Universal Day |publisher=Gutenberg.org |date=12 February 2006 |access-date=28 March 2016 |archive-date=18 December 2021 |archive-url=https://web.archive.org/web/20211218082731/https://www.gutenberg.org/files/17759/17759-h/17759-h.htm |url-status=live }}</ref>
|- 
| [[El Hierro|El Hierro (Ferro)]], <br> Canary Islands || 18° 03{{prime}} W, <br> {{nowrap|later redefined as}} <br> 17° 39{{prime}} 46{{pprime}} W 
| [[Ferro meridian]]
|{{Location map-line|lon=-18}}
|<ref>Ancient, used in [[Ptolemy]]'s ''[[Geographia]]''. Later redefined 17° 39{{prime}} 46{{pprime}} W of Greenwich to be exactly 20° W of Paris. French "submarin" at Washington 1884.</ref>
|-
| [[Tenerife]] || 16°38{{prime}}22{{pprime}} W
| [[Tenerife meridian]]
|{{Location map-line|lon=-16}}
| Rose to prominence with Dutch cartographers and navigators after they abandoned the idea of a magnetic meridian<ref>A.R.T. Jonkers;  [https://livrepository.liverpool.ac.uk/3000739/1/PARAMER.pdf Parallel meridians: Diffusion and change in early modern oceanic reckoning] {{Webarchive|url=https://web.archive.org/web/20180126070923/https://livrepository.liverpool.ac.uk/3000739/1/PARAMER.pdf |date=26 January 2018 }}, in ''Noord-Zuid in Oostindisch perspectief'', The Hague, 2005, p. 7. Retrieved 2 February 2015.</ref> 
|-
| [[Lisbon]] || 9° 07{{prime}} 54.862{{pprime}} W
|
|{{Location map-line|lon=-9}}
|<ref name="Bartky">{{cite book|last=Bartky|first=Ian R.|title=One Time Fits All: The Campaigns for Global Uniformity|url=https://books.google.com/books?id=rC6sAAAAIAAJ&pg=PA98|year=2007|publisher=Stanford University Press|isbn=978-0-8047-5642-6|page=98|access-date=8 December 2018|archive-date=22 January 2023|archive-url=https://web.archive.org/web/20230122160000/https://books.google.com/books?id=rC6sAAAAIAAJ&pg=PA98|url-status=live}}</ref>
|-
| [[Cadiz]] ||  6° 17{{prime}} 35.4" W  
| Cadiz meridian
|{{Location map-line|lon=-6}}
| Royal Observatory in southeast tower of [[:es:Castillo de la Villa (Cádiz)|Castillo de la Villa]], used 1735–1850 by Spanish Navy.<ref name="Cadiz1">[https://elpais.com/elpais/2017/01/02/inenglish/1483355711_147804.html "In search of the lost meridian of Cadiz"] {{Webarchive|url=https://web.archive.org/web/20191130014945/https://elpais.com/elpais/2017/01/02/inenglish/1483355711_147804.html |date=30 November 2019 }}, ''El País'', 23 December 2016. Retrieved 8 November 2018.</ref><ref name=Cadiz2>Antonio Lafuente and Manuel Sellés, [https://scholar.google.com/scholar?hl=en&as_sdt=0%2C10&q=El+Meridiano+de+C%C3%A1diz&btnG= El Observatorio de Cádiz (1753–1831)] {{Webarchive|url=https://web.archive.org/web/20200602035018/https://scholar.google.com/scholar?hl=en&as_sdt=0%2C10&q=El+Meridiano+de+C%C3%A1diz&btnG= |date=2 June 2020 }}, Ministerio de Defensa, 1988, p.144, {{isbn|84-505-7563-X}}. {{in lang|es}}</ref>
|- 
| [[Madrid]] || 3° 41{{prime}} 16.58{{pprime}} W 
|
|{{Location map-line|lon=-3}}
|<ref name="Bartky" />
|-
| [[Kew]] || 0° 00{{prime}} 19.0{{pprime}} W
| Prime Meridian (prior to Greenwich)
| rowspan="4" |{{Location map-line|lon=0}}
| Located at King George III's [[Kew Observatory]]
|-
| rowspan="3" | Greenwich || 0° 00{{prime}} 05.33{{pprime}} W 
| [[United Kingdom Ordnance Survey Zero Meridian]]
| [[James Bradley|Bradley]] Meridian{{sfn|Dolan|2013a}}
|-
| 0° 00{{prime}} 05.3101{{pprime}} W
| [[Prime meridian (Greenwich)|Greenwich meridian]]
| Airy Meridian{{sfn|Dolan|2013a}}
|-
| 0° 00{{prime}} 00.00{{pprime}} 
| [[IERS Reference Meridian]]
|
|- 
| [[Paris]] || 2° 20{{prime}} 14.025{{pprime}} E 
| [[Paris meridian]]
|{{Location map-line|lon=2}}
|
|- 
| [[Brussels]] || 4° 22{{prime}} 4.71{{pprime}} E 
|
| rowspan="3" |{{Location map-line|lon=4}}
|<ref name="Bartky" />
|- 
| [[Antwerp]] || 4° 24{{prime}} E 
| [[Antwerp meridian]]
| 
|- 
| [[Amsterdam]] || 4° 53{{prime}} E 
|
| Through the [[Westerkerk]] in Amsterdam; used to define the legal time in the Netherlands from 1909 to 1937<ref>{{in lang|nl}}[http://www.staff.science.uu.nl/~gent0113/wettijd/wt_text3d.htm Eenheid van tijd in Nederland (Unity of time in the Netherlands)] {{Webarchive|url=https://web.archive.org/web/20150210095902/http://www.staff.science.uu.nl/~gent0113/wettijd/wt_text3d.htm |date=10 February 2015 }}, Utrecht University website, retrieved 28 August 2013.</ref>
|- 
| [[Pisa]] || 10° 24{{prime}} E 
|
| rowspan="2" |{{Location map-line|lon=10}}
|{{sfn|Hooker|2006|loc=introduction}}
|- 
| [[Oslo|Oslo (Kristiania)]] || 10° 43{{prime}} 22.5{{pprime}} E
|
|{{sfn|Hooker|2006|loc=introduction}}<ref name="WIRED" />
|- 
| [[Florence]] || 11°15{{prime}} E 
| [[Florence meridian]]
|{{Location map-line|lon=11}}
| Used in the [[Peters projection]], 180° from a meridian running through the [[Bering Strait]]
|- 
| [[Rome]] || 12° 27{{prime}} 08.4{{pprime}} E 
| ''Meridian of [[Monte Mario]]''
| rowspan="2" |{{Location map-line|lon=12}}
| Used in Roma 40 Datum<ref>[http://www.asprs.org/a/resources/grids/08-2005-italy.pdf Grids & Datums – Italian Republic] {{Webarchive|url=https://web.archive.org/web/20121120145503/http://www.asprs.org/a/resources/grids/08-2005-italy.pdf |date=20 November 2012 }}, asprs.org, Retrieved 10 December 2013.</ref>
|- 
| [[Copenhagen]] || 12° 34{{prime}} 32.25{{pprime}} E 
|
| [[Rundetårn]]<ref>''[http://www.denstoredanske.dk/index.php?sideId=124327 meridian] {{Webarchive|url=https://web.archive.org/web/20160314105013/http://denstoredanske.dk/index.php?sideid=124327 |date=14 March 2016 }}'', article from [[Den Store Danske Encyklopædi]]</ref>
|-
| [[Naples]] || 14° 15{{prime}} E 
|
|{{Location map-line|lon=14}}
|<ref name="gutenberg.org"/>
|-
| [[Bratislava|Pressburg]] || 17° 06{{prime}} 03{{pprime}} E 
|Meridianus Posoniensis
|{{Location map-line|lon=17}}
|Used by [[Sámuel Mikoviny]] 
|- 
| [[Stockholm]] || 18° 03{{prime}} 29.8{{pprime}} E 
|
|{{Location map-line|lon=18}}
| At the [[Stockholm Observatory]]<ref name="Bartky" />
|- 
| [[Buda]] || 19° 03{{prime}} 37{{pprime}} E 
| Meridianu(s) Budense
| rowspan="2" |{{Location map-line|lon=19}}
| Used between 1469 and 1495; introduced by [[Regiomontanus]], used by [[Marcin Bylica]], [[Galeotto Marzio]], Miklós Erdélyi (1423–1473), Johannes Tolhopff (c. 1445–1503), Johannes Muntz. Set in the royal castle (and observatory) of Buda.{{Efn|When Tolhopff handed over his book, titled {{lang|la|Stellarium}} (1480),<ref>{{cite book |title=Stellarium |first=Johannes |last=Tolhopff |date=1480 |url=https://www.corvina.oszk.hu/kepnezegeto/index.php?corvina=codguelf84_1aug2o&lang=en&img=11#11 |language=la |access-date=30 December 2021 |archive-date=30 December 2021 |archive-url=https://web.archive.org/web/20211230012913/https://www.corvina.oszk.hu/kepnezegeto/index.php?corvina=codguelf84_1aug2o&lang=en&img=11#11 |url-status=live }} (facsimile, not machine readable)</ref>  to King Matthias Corvinus, he emphasized that he had used the meridian of [[Buda]] for his calculations. The German physician, Johannes Müntz used it the same way in his 1495 calendar. However, in the second edition, he used the Vienna meridian.<ref>{{cite journal | last=Zsoldos |first=Endre |journal=Orpheus Noster |volume= 5 |number= 4 |pages= 64–87 |date=2014 |title=Stellarium – egy csillagászati kódex Mátyás könyvtárában |trans-title=Stellarium - an Astronomical Codex in the Library of King Matthias |url=https://www.academia.edu/8257327|language=hu}}</ref><ref>{{cite journal |last=Szathmáry |first=László |title=Az asztrológia, alkémia és misztika Mátyás király udvarában. |trans-title=Astrology, alchemy and mysticism in the court of King Matthias. |journal=Ponticulus Hungaricus |volume=VI. évfolyam 5. szám |date=2002 |url=http://members.iif.hu/visontay/ponticulus/rovatok/hidverok/matyas-01.html |url-status=dead |language=hu |access-date=27 December 2018 |archive-date=18 October 2009 |archive-url=https://web.archive.org/web/20091018162305/http://members.iif.hu/visontay/ponticulus/rovatok/hidverok/matyas-01.html }}</ref>}} 
|- 
| [[Kraków]] || 19° 57{{prime}} 21.43{{pprime}} E 
| Kraków meridian
| at the Old Kraków Observatory at the [[Botanic Garden of the Jagiellonian University|Śniadecki' College]]; mentioned also in [[Nicolaus Copernicus]]'s work ''On the Revolutions of the Heavenly Spheres''.
|- 
| [[Warsaw]] || 21° 00{{prime}} 42{{pprime}} E
| [[Warsaw meridian]]
|{{Location map-line|lon=21}}
|<ref name="Bartky" />
|- 
| [[History of Oradea|Várad]] || 21° 55{{prime}} 16{{pprime}} E 
| {{lang|la|Tabulae Varadienses}}
|{{Location map-line|lon=21}}
|<ref>{{cite web |url=http://romaniatourism.com/oradea.html |title=Oradea |publisher=Romania Tourism |access-date=3 February 2015 |archive-date=6 February 2015 |archive-url=https://web.archive.org/web/20150206142118/http://romaniatourism.com/oradea.html |url-status=live }}</ref> Between 1464 and 1667, a ''prime meridian'' was set in the Fortress of Oradea (''Varadinum'' at the time) by [[Georg von Peuerbach]].<ref>{{Cite web |date=2015 |title=Romanian astronaut marks 10th anniversary of Prime Meridian Astronomy Club |url=http://www.nineoclock.ro/romanian-astronaut-marks-10th-anniversary-of-prime-meridian-astronomy-club/ |website=NineO'Clock |access-date=26 June 2017 |archive-date=1 October 2017 |archive-url=https://web.archive.org/web/20171001075121/http://www.nineoclock.ro/romanian-astronaut-marks-10th-anniversary-of-prime-meridian-astronomy-club/ |url-status=live }}</ref> In his logbook [[Christopher Columbus|Columbus]] stated, he had one copy of Tabulae Varadienses ({{lang|la|Tabula Varadiensis}} or {{lang|la|Tabulae directionum}}) on board to calculate the actual meridian based on the position of the Moon, in correlation to Várad. [[Amerigo Vespucci]] also recalled, how was he acquired the knowledge to calculate meridians by means of these tables.<ref>{{cite web |url=http://meridianzero.astroclubul.org/istoric_hu.html |title=Meridian Zero csillagászklub |access-date=27 December 2018 |language=ro |archive-date=12 April 2009 |archive-url=https://web.archive.org/web/20090412084006/http://www.meridianzero.ro/istoric_hu.html |url-status=live }}</ref>
|- 
| [[Alexandria]] || 29° 53{{prime}} E 
| Meridian of Alexandria
|{{Location map-line|lon=29}}
| The meridian of [[Ptolemy]]'s [[Almagest]].
|- 
| [[Saint Petersburg]] || 30° 19{{prime}} 42.09{{pprime}} E
| [[Pulkovo meridian]]
|{{Location map-line|lon=30}}
|
|- 
| {{nowrap|[[Great Pyramid of Giza]]}} || 31° 08{{prime}} 03.69{{pprime}} E 
|
|{{Location map-line|lon=31}}
| 1884<ref>Wilcomb E. Washburn, "[http://muweb.millersville.edu/~columbus/data/geo/WASHBR04.GEO The Canary Islands and the Question of the Prime Meridian: The Search for Precision in the Measurement of the Earth] {{webarchive|url=https://web.archive.org/web/20070529031631/http://muweb.millersville.edu/~columbus/data/geo/WASHBR04.GEO |date=29 May 2007 }}"</ref>
|- 
| [[Jerusalem]] || 35° 13{{prime}} 47.1{{pprime}} E 
|
|{{Location map-line|lon=35}}
|<ref name="WIRED" />
|- 
| [[Mecca]] || 39° 49{{prime}} 34{{pprime}} E 
|
|{{Location map-line|lon=39}}
| See also [[Mecca Time]]
|-
| || Approx. 59° E
|
|{{Location map-line|lon=59}}
|[[Maimonides]]<ref>[http://mechon-mamre.org/i/3811.htm#17 ''Hilchot Kiddush Hachodesh'' 11:17]</ref> calls this point (24 degrees east of [[Jerusalem]]) אמצע היישוב, "the middle of the habitation", i.e. the habitable hemisphere. Evidently this was a convention accepted by Arab geographers of his day.
|- 
| [[Ujjain]] || 75° 47{{prime}} E 
|
|{{Location map-line|lon=75}}
| Used from 4th century CE Indian astronomy and calendars(see also [[Time in India#Ancient India|Time in India]]).{{sfn|Burgess|1860}}
|- 
| [[Beijing]] || 116° 24{{prime}} E 
|
|{{Location map-line|lon=116}}
| Used in [[Qing Dynasty]] for astronomical<ref>{{cite web |title=御製厯象考成下篇 |language=zh-hant |url=https://zh.wikisource.org/wiki/%E5%BE%A1%E8%A3%BD%E5%8E%AF%E8%B1%A1%E8%80%83%E6%88%90_(%E5%9B%9B%E5%BA%AB%E5%85%A8%E6%9B%B8%E6%9C%AC)/%E4%B8%8B%E7%B7%A8%E5%8D%B701#%E6%8E%A8%E5%90%84%E7%9C%81%E7%AF%80%E6%B0%A3%E6%99%82%E5%88%BB%E6%B3%95}}</ref><ref>{{cite web |title=清史稿 |language=zh-hant |url=https://zh.wikisource.org/wiki/%E6%B8%85%E5%8F%B2%E7%A8%BF/%E5%8D%B748}}</ref> and cartographical<ref>{{cite web|url=http://news.eastday.com/epublish/gb/paper148/20010726/class014800009/hwz447203.htm|title=新闻精选-我国清代世界地图以北京为本初子午线|language=zh-hans|website=news.eastday.com|accessdate=2012-05-04|archive-date=2016-03-04|archive-url=https://web.archive.org/web/20160304200732/http://news.eastday.com/epublish/gb/paper148/20010726/class014800009/hwz447203.htm|url-status=live}}</ref> purposes.
|- 
| [[Kyoto]] || 136° 14{{prime}} E 
|
|{{Location map-line|lon=136}}
| Used in 18th and 19th (officially 1779–1871) century Japanese maps. Exact place unknown, but in "Kairekisyo" in Nishigekkoutyou-town in Kyoto, then the capital.{{citation needed|date=July 2013}}
|-
| || ~ 180 
|
|[[File:Earth map with 180th meridian.jpg|thumb|300px|180th meridian]]
| Opposite of Greenwich, proposed 13 October 1884 on the International Meridian Conference by [[Sandford Fleming]]<ref name="gutenberg.org"/>
|}

==See also==
* {{Annotated link |1st meridian east}}
* {{Annotated link |1st meridian west}}
* {{Annotated link |180th meridian}}
* {{Annotated link |Null Island}}
* {{Annotated link |Geographical center of Earth}}

==Notes==
{{notelist}}

==References==
{{Reflist|30em}}

==Works cited==
{{refbegin|30em|indent=yes}}
*{{Citation
| last    = Burgess
| first   = Ebenezer
| publication-date = 2013
| date = 1860
| title    = Journal of the American Oriental Society
| contribution = Translation of the Surya-Siddhanta
| type    = e-book
| volume  = 6
| page  = 185
}}
*{{cite web
|last = Dolan
|first = Graham
|url = http://www.thegreenwichmeridian.org/tgm/articles.php?article=8
|work = The Greenwich Meridian
|title = The Greenwich Meridian before the Airy Transit Circle
|date = 2013a
|access-date = 6 January 2013
|archive-date = 2 May 2012
|archive-url = https://web.archive.org/web/20120502225626/http://www.thegreenwichmeridian.org/tgm/articles.php?article=8
|url-status = live
}}
*{{cite web
|last = Dolan
|first = Graham
|url = http://www.thegreenwichmeridian.org/tgm/articles.php?article=7
|work = The Greenwich Meridian
|title = WGS84 and the Greenwich Meridian
|date = 2013b
|access-date = 6 January 2013
|archive-date = 8 July 2014
|archive-url = https://web.archive.org/web/20140708074531/http://www.thegreenwichmeridian.org/tgm/articles.php?article=7
|url-status = live
}}
*{{citation |first=Brian |last=Hooker |title=A multitude of prime meridians |date=2006 |url=http://zeehaen.tripod.com/unpub_2/multitude_meridians.htm |access-date=28 June 2019 |archive-url=https://web.archive.org/web/20180926052301/http://zeehaen.tripod.com/unpub_2/multitude_meridians.htm |archive-date=26 September 2018 }}
*{{citation | last = Howse | first = Derek | title = Greenwich Time and the Longitude | date = 1997 | publisher = Phillip Wilson | isbn = 978-0-85667-468-6 | url-access = registration | url = https://archive.org/details/greenwichtimelon0000hows }}
*{{citation |first1=Jean |first2=Martin |last1=Norgate |last2=Norgate |date=2006 |title=Prime meridian |url=https://www.oldhampshiremapped.org.uk/hantsmap/meridian.htm |website=Old Hampshire Mapped |access-date=13 January 2013 |archive-date=28 December 2021 |archive-url=https://web.archive.org/web/20211228152854/https://www.oldhampshiremapped.org.uk/hantsmap/meridian.htm |url-status=live }}
*{{citation | title = NGS datasheet station name form | date = 2016 | publisher = National Geodetic Survey | url = http://www.ngs.noaa.gov/cgi-bin/ds_desig.prl | access-date = 11 December 2016 | ref = {{SfnRef|NGS|2016}} | archive-date = 16 February 2016 | archive-url = https://web.archive.org/web/20160216184812/http://www.ngs.noaa.gov/cgi-bin/ds_desig.prl | url-status = live }}
*{{citation |first1=Dava |last1=Sobel |first2=William J. H. |last2=Andrewes |title=The Illustrated Longitude |date=1998 |publisher=Fourth Estate, London|title-link=The Illustrated Longitude }}
{{refend}}

==External links==
{{commons category|Prime meridian}}
* [https://books.google.com/books?id=qOIDAAAAMBAJ&pg=PA927 "Where the Earth's surface begins—and ends"], ''Popular Mechanics'', December 1930
* [http://www.ucolick.org/~sla/leapsecs/scans-meridian.html scanned TIFFs of the conference proceedings]
* [https://web.archive.org/web/20061029234822/http://wwp.greenwichmeantime.com/info/prime-meridian.htm Prime meridians in use in the 1880s, by country]

{{Time measurement and standards}}
{{geographical coordinates}}
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{{Authority control}}
<!-- interwiki links referring to the GRAN shall be placed at [[Prime meridian (Greenwich)]] -->

[[Category:Geodesy]]
[[Category:Meridians (geography)]]
[[Category:Prime meridians| ]]
[[Category:Cardinal Richelieu]]