Editing Prime meridian (section)

===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]]
|- 
|}