IERS Reference Meridian

Prime Meridian0° longitudeIERS meridianIERS origininternational reference meridian
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).wikipedia
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Prime meridian

GreenwichGreenwich meridianGreenwich Prime Zero meridian
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).
The most widely used modern meridian is the IERS Reference Meridian.

World Geodetic System

WGS84WGS 84GPS coordinates
It is also the reference meridian of the Global Positioning System (GPS) 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).
The WGS 84 meridian of zero longitude is the IERS Reference Meridian, 5.3 arc seconds or 102 m east of the Greenwich meridian at the latitude of the Royal Observatory.

International Earth Rotation and Reference Systems Service

IERSInternational Earth Rotation ServiceEarth Orientation parameters
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 defined the IERS Reference Meridian, the International Terrestrial Reference System (ITRS), and subsequent International Terrestrial Reference Frames (ITRF).

Royal Observatory, Greenwich

Royal Greenwich ObservatoryRoyal ObservatoryGreenwich Observatory
It passes about 5.3 arcseconds east of George Biddell Airy's 1851 transit circle or 102 m at the latitude of the Royal Observatory, Greenwich.
International time from the end of the 19th century until UT1 was based on Simon Newcomb's equations, giving a mean sun about 0.18 seconds behind UT1 (the equivalent of 2.7 arcseconds) as of 2013; it coincided in 2013 with a meridian halfway between Airy's circle and the IERS origin: 51.47781°N, -0.00072°W.

Western Hemisphere

WesternhemisphereAmericas
The 180th meridian is opposite the IERS Reference Meridian and forms a great circle with it dividing the earth into Western Hemisphere and Eastern Hemisphere.
Below is a list of the sovereign states which are in both the Western and Eastern Hemispheres on the IERS Reference Meridian, in order from north to south:

Coordinated Universal Time

UTCUTC-3UTC-4
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 second.
Thus, the time system would lose its fixed connection to the geographic coordinates based on the IERS meridian.

Minute and second of arc

masarcsecondarc second
It passes about 5.3 arcseconds east of George Biddell Airy's 1851 transit circle or 102 m at the latitude of the Royal Observatory, Greenwich.

George Biddell Airy

George AiryAirySir George Biddell Airy
It passes about 5.3 arcseconds east of George Biddell Airy's 1851 transit circle or 102 m at the latitude of the Royal Observatory, Greenwich.

Meridian circle

transit circlemural circletransit
It passes about 5.3 arcseconds east of George Biddell Airy's 1851 transit circle or 102 m at the latitude of the Royal Observatory, Greenwich.

Latitude

latitudesSouthlatitudinal
It passes about 5.3 arcseconds east of George Biddell Airy's 1851 transit circle or 102 m at the latitude of the Royal Observatory, Greenwich.

Global Positioning System

GPSglobal positioning systemsGlobal Positioning System (GPS)
It is also the reference meridian of the Global Positioning System (GPS) 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).

United States Department of Defense

Department of DefenseU.S. Department of DefenseUS Department of Defense
It is also the reference meridian of the Global Positioning System (GPS) 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).

International Terrestrial Reference System and Frame

International Terrestrial Reference SystemInternational Terrestrial Reference FrameITRF
It is also the reference meridian of the Global Positioning System (GPS) 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).

Vertical deflection

deflection of the verticaldeflectionsdeflections of the vertical
The reason for the 5.3 arcsecond 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.

Geodetic datum

datumGeodetic systemgeodetic
The reason for the 5.3 arcsecond 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.

International Hydrographic Organization

IHOInternational Hydrographic OrganisationInternational Hydrographic Bureau
The International Hydrographic Organization adopted an early version of the IRM in 1983 for all nautical charts.

International Civil Aviation Organization

ICAOICAO recommendations on use of the International System of UnitsInternational Civil Aviation Organization (ICAO)
The IRM was adopted for air navigation by the International Civil Aviation Organization on 3 March 1989.

Plate tectonics

tectonic platesplate tectonictectonic
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.

Least squares

least-squaresmethod of least squaresleast squares method
Thus this 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.

Satellite laser ranging

International Laser Ranging Servicelaser rangingSLR
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.

Lunar Laser Ranging experiment

lunar laser rangingLLRLunar Laser Ranging experiments
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.

Very-long-baseline interferometry

VLBIVery Long Baseline Interferometrylong-baseline interferometry
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.

180th meridian

180°antimeridianAnti-Meridian
The 180th meridian is opposite the IERS Reference Meridian and forms a great circle with it dividing the earth into Western Hemisphere and Eastern Hemisphere.

Great circle

Great Circle Routegreat circlesarcs of great circle
The 180th meridian is opposite the IERS Reference Meridian and forms a great circle with it dividing the earth into Western Hemisphere and Eastern Hemisphere.