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Modern IERS Reference Meridian on Earth

The IERS Reference Meridian (IRM), also called the International Reference Meridian, is the prime meridian (0° longitude) maintained by the International Earth Rotation and Reference Systems Service (IERS). It passes about 5.3 arcseconds east of George Biddell Airy's 1851 transit circle, and thus it differs slightly from the historical Greenwich Meridian. At the latitude of the Royal Observatory, Greenwich the difference is 102 metres (335 ft).^[1]^[2]^[a]

It is the reference meridian of the Global Positioning System (GPS) operated by the United States Space Force, and of WGS 84 and its two formal versions, the ideal International Terrestrial Reference System (ITRS) and its realization, the International Terrestrial Reference Frame (ITRF).

Location

The most important reason for the 5.3 seconds of longitude offset between the IERS Reference Meridian and the Airy transit circle is that the observations with the transit circle were based on the local vertical, while the IERS Reference is a geodetic longitude, that is, the plane of the meridian contains the center of mass of the Earth.^[1]

The International Hydrographic Organization adopted an early version of the IRM in 1983 for all nautical charts.^[3] It was adopted for air navigation by the International Civil Aviation Organization on 3 March 1989.^[4] Tectonic plates slowly move over the surface of Earth, so most countries have adopted for their maps an IRM version fixed relative to their own tectonic plate as it existed at the beginning of a specific year. Examples include the North American Datum 1983 (NAD83), the European Terrestrial Reference Frame 1989 (ETRF89), and the Geocentric Datum of Australia 1994 (GDA94). Versions fixed to a tectonic plate differ from the global version by at most a few centimetres.

The IERS system is not quite fixed to any point attached to the Earth. For example, all points on the European portion of the Eurasian plate, including the Royal Observatory, are moving northeast at about 2.5 cm per year relative to it. The IRM is the weighted average (in the least squares sense) of the reference meridians of the hundreds of ground stations contributing to the IERS network. The network includes GPS stations, satellite laser ranging (SLR) stations, lunar laser ranging (LLR) stations, and the highly accurate very long baseline interferometry (VLBI) stations.^[5] All stations' coordinates are adjusted annually to remove net rotation relative to the major tectonic plates. If earth had only two hemispherical plates moving relative to each other around any axis which intersects their centres or their junction, then the longitudes (around any other rotation axis) of any two, diametrically opposite, stations must move in opposite directions by the same amount. The 180th meridian (the meridian at 180° both east and west of the Prime Meridian) is opposite the IERS Reference Meridian and forms a great circle with it dividing the earth into Western Hemisphere and Eastern Hemisphere.

Universal Time is notionally based on the prime meridian.^[6] Because of changes in the rate of Earth's rotation, standard international time UTC can differ from the mean observed solar time at noon on the prime meridian by up to 0.9 of a second. Leap seconds are inserted from time to time, to keep UTC close to Earth's angular position relative to the Sun; see mean solar time.

List of places

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Starting at the North Pole and heading south to the South Pole, the IERS Reference Meridian passes through eight countries and three oceans (Arctic Ocean, Atlantic Ocean and Southern Ocean):

Co-ordinates (approximate)	Country, territory or sea	Notes
90°0′N 0°0′E / 90.000°N 0.000°E / 90.000; 0.000 (North Pole)	Arctic Ocean
85°46′N 0°0′E / 85.767°N 0.000°E / 85.767; 0.000 (EEZ of Greenland (Denmark))	Exclusive Economic Zone (EEZ) of Greenland (Denmark)
81°39′N 0°0′E / 81.650°N 0.000°E / 81.650; 0.000 (Greenland Sea)	Greenland Sea
80°29′N 0°0′E / 80.483°N 0.000°E / 80.483; 0.000 (EEZ of Svalbard (Norway))	EEZ of Svalbard (Norway)
76°11′N 0°0′E / 76.183°N 0.000°E / 76.183; 0.000 (International waters)	International waters
73°44′N 0°0′E / 73.733°N 0.000°E / 73.733; 0.000 (EEZ of Jan Mayen)	EEZ of Jan Mayen (Norway)
72°53′N 0°0′E / 72.883°N 0.000°E / 72.883; 0.000 (Norwegian Sea)	Norwegian Sea
69°7′N 0°0′E / 69.117°N 0.000°E / 69.117; 0.000 (International waters)	International waters
64°42′N 0°0′E / 64.700°N 0.000°E / 64.700; 0.000 (EEZ of Norway)	EEZ of Norway
63°29′N 0°0′E / 63.483°N 0.000°E / 63.483; 0.000 (EEZ of Great Britain)	EEZ of Great Britain
61°0′N 0°0′E / 61.000°N 0.000°E / 61.000; 0.000 (North Sea)	North Sea
53°46′N 0°0′E / 53.767°N 0.000°E / 53.767; 0.000 (United Kingdom)	United Kingdom	From Tunstall in East Riding to Peacehaven, passing through Greenwich
50°47′N 0°0′E / 50.783°N 0.000°E / 50.783; 0.000 (English Channel)	English Channel	EEZ of Great Britain
50°14′N 0°0′E / 50.233°N 0.000°E / 50.233; 0.000 (EEZ of France)	English Channel	EEZ of France
49°20′N 0°0′E / 49.333°N 0.000°E / 49.333; 0.000 (France)	France	From Villers-sur-Mer to Gavarnie
42°41′N 0°0′E / 42.683°N 0.000°E / 42.683; 0.000 (Spain)	Spain	From Cilindro de Marboré to Castellón de la Plana
39°56′N 0°0′E / 39.933°N 0.000°E / 39.933; 0.000 (Mediterranean Sea)	Mediterranean Sea	Gulf of Valencia; EEZ of Spain
38°52′N 0°0′E / 38.867°N 0.000°E / 38.867; 0.000 (Spain)	Spain	From El Verger to Calp
38°38′N 0°0′E / 38.633°N 0.000°E / 38.633; 0.000 (Mediterranean Sea)	Mediterranean Sea	EEZ of Spain
37°1′N 0°0′E / 37.017°N 0.000°E / 37.017; 0.000 (EEZ of Algeria)	Mediterranean Sea	EEZ of Algeria
35°50′N 0°0′E / 35.833°N 0.000°E / 35.833; 0.000 (Algeria)	Algeria	From Stidia to Algeria-Mali border near Bordj Badji Mokhtar
21°52′N 0°0′E / 21.867°N 0.000°E / 21.867; 0.000 (Mali)	Mali	Passing through Gao
15°00′N 0°0′E / 15.000°N 0.000°E / 15.000; 0.000 (Burkina Faso)	Burkina Faso
11°7′N 0°0′E / 11.117°N 0.000°E / 11.117; 0.000 (Togo)	Togo	For about 600 m
11°6′N 0°0′E / 11.100°N 0.000°E / 11.100; 0.000 (Ghana)	Ghana	For about 16 km
10°58′N 0°0′E / 10.967°N 0.000°E / 10.967; 0.000 (Togo)	Togo	For about 39 km
10°37′N 0°0′E / 10.617°N 0.000°E / 10.617; 0.000 (Ghana)	Ghana	From the Togo-Ghana border near Bunkpurugu to Tema Passing through Lake Volta at 7°46′N 0°0′E / 7.767°N 0.000°E / 7.767; 0.000 (Lake Volta)
5°37′N 0°0′E / 5.617°N 0.000°E / 5.617; 0.000 (EEZ of Ghana in Atlantic Ocean)	Atlantic Ocean	EEZ of Ghana
1°58′N 0°0′E / 1.967°N 0.000°E / 1.967; 0.000 (International waters)		International waters
0°0′N 0°0′E / 0.000°N 0.000°E / 0.000; 0.000 (Equator)		Passing through the Equator (see Null Island)
51°43′S 0°0′E / 51.717°S 0.000°E / -51.717; 0.000 (EEZ of Bouvet Island)		EEZ of Bouvet Island (Norway)
57°13′S 0°0′E / 57.217°S 0.000°E / -57.217; 0.000 (International waters)		International waters
60°0′S 0°0′E / 60.000°S 0.000°E / -60.000; 0.000 (Southern Ocean)	Southern Ocean	International waters
69°36′S 0°0′E / 69.600°S 0.000°E / -69.600; 0.000 (Antarctica)	Antarctica	Queen Maud Land, claimed by Norway
90°0′S 0°0′E / 90.000°S 0.000°E / -90.000; 0.000	Antarctica	Amundsen–Scott South Pole Station, United States South Pole

References

Notes

^ The astronomic latitude of the Royal Observatory is 51°28'38"N whereas its latitude on the European Terrestrial Reference Frame (1989) datum is 51°28'40.1247"N.

Citations

^ ^a ^b Malys, Stephen; Seago, John H.; Palvis, Nikolaos K.; Seidelmann, P. Kenneth; Kaplan, George H. (1 August 2015). "Why the Greenwich meridian moved". Journal of Geodesy. 89 (12): 1263–1272. Bibcode:2015JGeod..89.1263M. doi:10.1007/s00190-015-0844-y.
^ IRM on grounds of Royal Observatory from Google Earth Accessed 30 March 2012
^ "A manual on the technical aspects of the United Nations Convention on the Law of the Sea – 1982" (PDF). Archived from the original (PDF) on 2008-09-10. Retrieved 2012-03-28. (4.89 MB) Section 2.4.4.
^ WGS 84 Implementation Manual Archived 2008-10-03 at the Wayback Machine page i, 1998
^ McCarthy, Dennis D.; Petit, Gérard, eds. (2004), "Conventional Terrestrial Reference System and Frame", IERS Conventions (2003) (Technical report), IERS Technical Note, 32, retrieved 2021-07-23
^ ITU Radiocommunication Assembly (2002). "Standard-frequency and time-signal emissions" (PDF). International Telecommunication Union. Retrieved 5 February 2022.