Prime Meridian

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Prime Meridian

The Prime Meridian is the meridian

Meridian (geography)

A meridian is an imaginary arc on the Earth's surface from the North Pole to the South Pole that connects all locations running along it with a given longitude....
(line of longitude

Longitude

Longitude , symbolized by the Greek character lambda , is the geographic coordinate most commonly used in cartography and global navigation for east-west measurement....
) at which longitude is defined to be 0°.

The Prime Meridian and the opposite 180th meridian

180th meridian

The 180th meridian or antimeridian is the meridian defined as 180? longitude. It is the line of longitude exactly opposite the Prime Meridian....
(at 180° longitude), which the International Date Line

International Date Line

The International Date Line is an imaginary line on the surface of the Earth opposite the Prime Meridian where the date changes as one travels east or west across it....
generally follows, form a great circle

Great circle

A great circle of a sphere is a circle that runs along the surface of that sphere so as to cut it into two equal halves. The great circle therefore has both the same circumference and the same center as the sphere....
that divides the Earth

Earth

Earth is the third planet from the Sun. Earth is the largest of the terrestrial planets in the Solar System in diameter, mass and density. It is also referred to as the World and Wiktionary:Terra.Note that by International Astronomical Union convention, the term "Terra" is used for naming extensive land masses, rather...
into the Eastern

Eastern Hemisphere

The Eastern Hemisphere, also Eastern hemisphere or eastern hemisphere, is a geography term for the half of the Earth that is east of the Prime Meridian and west of 180? longitude....
and Western Hemisphere

Western Hemisphere

The Western Hemisphere, also Western hemisphere or western hemisphere, is a geography term for the half of the Earth that lies west of the Prime Meridian , the other half being the Eastern Hemisphere....
s.

Unlike the parallels of latitude

Latitude

Latitude, usually denoted symbolically by the Greek letter phi gives the location of a place on Earth north or south of the equator. Lines of Latitude are the horizontal lines shown running east-to-west on maps ....
, which are defined by the rotational axis of the Earth (the poles

Geographical pole

A geographical pole , is either of two points on the surface of a spinning planet or other spinning body, at 90 degrees from its equator, at one of the two points where the Axis of rotation around which the body spins meets the surface of the body....
being 90° and the Equator

Equator

The equator is the intersection of the Earth's surface with the Plane perpendicular to the Earth's rotation and containing the Earth's center of mass....
0°), the Prime Meridian is arbitrary.

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Geography

Starting at the North Pole

North Pole

The North Pole, also known as the Geographic North Pole or Terrestrial North Pole is, subject to the caveats explained below, defined as the point in the northern hemisphere where the Earth's axis of rotation meets the Earth's surface....
and heading south to the South Pole

South Pole

The South Pole, also known as the Geographic South Pole or Terrestrial South Pole, is one of the two points where the Earth's rotation intersects the surface....
, the Prime Meridian passes through:

lat	Country, territory or sea	Notes
90° North Pole The North Pole, also known as the Geographic North Pole or Terrestrial North Pole is, subject to the caveats explained below, defined as the point in the northern hemisphere where the Earth's axis of rotation meets the Earth's surface.... 80° 80th parallel north The 80th parallel north is a circle of latitude that is 80 degree true north of the Earth equator, in the Arctic.Starting at the Prime Meridian and heading eastwards, the parallel 80? north passes through:... 75° 75th parallel north The 75th parallel north is a circle of latitude that is 75 degree true north of the Earth equator, in the Arctic.Starting at the Prime Meridian and heading eastwards, the parallel 75? north passes through:...	Arctic Ocean Arctic Ocean The Arctic Ocean, located in the Northern Hemisphere and mostly in the Arctic North Pole region, is the smallest and shallowest of the world's five major oceanic divisions....
70° 70th parallel north The 70th parallel north is a circle of latitude that is 70 degree true north of the Earth equator.Starting at the Prime Meridian and heading eastwards, the parallel 70? north passes through:... 65° 65th parallel north The 65th parallel north is a circle of latitude that is 65 degree true north of the Earth equator.Starting at the Prime Meridian and heading eastwards, the parallel 65? north passes through:...	Norwegian Sea Norwegian Sea The Norwegian Sea is part of the North Atlantic Ocean northwest of Norway, located between the North Sea and the Greenland Sea.It adjoins the Iceland Sea to the west and the Barents Sea to the northeast....
60° 60th parallel north The 60th parallel north is a circle of latitude that is 60 degree true north of the Earth equator.Starting at the Prime Meridian and heading eastwards, the parallel 60? north passes through:... 55° 55th parallel north The 55th parallel north is a circle of latitude that is 55 degree true north of the Earth equator.Starting at the Prime Meridian and heading eastwards, the parallel 55? north passes through:...	North Sea North Sea The North Sea is a marginal sea, epeiric sea on the European continental shelf. The Dover Strait and the English Channel in the south and the Norwegian Sea in the north connect it to the Atlantic Ocean....
53° 53rd parallel north The 53rd parallel north is a circle of latitude that is 53 degree true north of the Earth equator.Starting at the Prime Meridian and heading eastwards, the parallel 53? north passes through:... 52° 52nd parallel north The 52nd parallel north is a circle of latitude that is 52 degree true north of the Earth equator.In Canada, part of the border between Quebec and Newfoundland and Labrador is defined by the parallel.... 51° 51st parallel north The 51st parallel north is a circle of latitude that is 51 degree true north of the Earth equator.Starting at the Prime Meridian and heading eastwards, the parallel 51? north passes through:...		The most northerly land on the meridian is the shore (53°45'34?N) southeast of the Sand-le-Mere caravan park east of Kingston upon Hull Kingston upon Hull Kingston upon Hull , almost invariably referred to as Hull, is a City status in the United Kingdom and unitary authority area in the East Riding of Yorkshire, England....
50° 50th parallel north The 50th parallel north is a circle of latitude that is 50 degree true north of the Earth equator.Starting at the Prime Meridian and heading eastwards, the parallel 50? north passes through:...	English Channel English Channel The English Channel is an Arm of the Atlantic Ocean that separates England from northern France, and joins the North Sea to the Atlantic. It is about long and varies in width from at its widest, to only in the Strait of Dover....
49° 49th parallel north The 49th parallel north is a circle of latitude that is 49 degree true north of the Earth equator.The parallel forms part of the United States-Canadian Border from British Columbia to Manitoba on the Canada side and from Washington to Minnesota on the United States side, or from the Strait of Georgia to the Lake of the Woods.... 48° 48th parallel north The 48th parallel north is a circle of latitude that is 48 degree true north of the Earth equator.... 47° 47th parallel north The 47th parallel north is a circle of latitude that is 47 degree true north of the Earth equator.Starting at the Prime Meridian and heading eastwards, the parallel 47? north passes through:... 46° 46th parallel north The 46th parallel north is a circle of latitude that is 46 degree true north of the Earth equator.Starting at the Prime Meridian and heading eastwards, the parallel 46? north passes through:... 45° 44° 44th parallel north The 44th parallel north is a circle of latitude that is 44 degree true north of the Earth equator.Starting at the Prime Meridian and heading eastwards, the parallel 44? north passes through:... 43° 43rd parallel north The 43rd parallel north is a circle of latitude that is 43 degree true north of the Earth equator.Starting at the Prime Meridian and heading eastwards, the parallel 43? north passes through:...
42° 42nd parallel north The 42nd parallel north is a circle of latitude that is 42 degree true north of the Earth equator.Starting at the Prime Meridian and heading eastwards, the parallel 42? north passes through:... 41° 41st parallel north The 41st parallel north is a circle of latitude that is 41 degree true north of the Earth equator.Starting at the Prime Meridian and heading eastwards, the parallel 41? north passes through:... 40° 40th parallel north The 40th parallel north is a circle of latitude that is 40 degree true north of the Earth equator.Starting at the Prime Meridian and heading eastwards, the parallel 40? north passes through:...
39° 39th parallel north The 39th parallel north is a circle of latitude that is 39 degree true north of the Earth equator.Starting at the Prime Meridian and heading eastwards, the parallel 39? north passes through:... 38° 38th parallel north The 38th parallel north is a circle of latitude that is 38 degree true north of the Earth equator. The 38th parallel north has been especially important in the recent history of Korea.... 37° 37th parallel north The 37th parallel north is a circle of latitude that is 37 degree true north of the Earth equator.Starting at the Prime Meridian and heading eastwards, the parallel 37? north passes through:... 36° 36th parallel north The 36th parallel north is a circle of latitude that is 36 degree true north of the Earth equator.Starting at the Prime Meridian and heading eastwards, the parallel 36? north passes through:...	Mediterranean Sea Mediterranean Sea The Mediterranean Sea is a sea or Ocean off the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Europe, on the south by Africa, and on the east by Asia....	Gulf of Valencia Gulf of Valencia The Gulf of Valencia , is a Headlands and bays or inlet of the western Mediterranean Sea, on the eastern coast of Spain, its extremes are the Cabo de la Nao in the south while the north limit is difuse, for some it is the Cape of Vinar?s and for others it would be the Ebro delta; if Vinar?s cape is considered, then it is entirely comprised b...
35° 35th parallel north The 35th parallel north is a circle of latitude that is 35 degree true north of the Earth equator.In the United States, the parallel defines the southern border of Tennessee, and the border between North Carolina and Georgia .... 30° 30th parallel north The 30th parallel north is a circle of latitude that is 30 degree true north of the Earth equator. It stands one-third of the way between the equator and the North Pole.... 25° 25th parallel north The 25th parallel north is a circle of latitude that is 25 degree true north of the Earth equator, just north of the Tropic of Cancer.The northernmost section of the border between Mauritania and Mali is defined by the parallel....		Sahara Sahara The Sahara is the world's largest hot desert. At over 9,000,000 square kilometers , it covers most of Northern Africa, making it almost as large as the United States or the continent of Europe....
20° 20th parallel north The 20th parallel north is a circle of latitude that is 20 degree true north of the Earth equator.The parallel defines part of the border between Libya and Sudan, and within Sudan it defines the border between the Northern, Sudan and North Darfur states.... 15° 15th parallel north The 15th parallel north is a circle of latitude that is 15 degree true north of the Earth equator.In the Chadian-Libyan conflict of 1978 to 1987, the parallel, known as the "Red Line", delineated areas controlled by opposing combatants....		Sahara Sahara The Sahara is the world's largest hot desert. At over 9,000,000 square kilometers , it covers most of Northern Africa, making it almost as large as the United States or the continent of Europe.... , Sahel Sahel File:Sahel Map-Africa rough.pngFile:AT0713 map.pngThe Sahel or Sahel Belt is a semi-arid tropical and subtropical grasslands, savannas, and shrublands ecoregion in Africa, which forms the transition between the Sahara to the north and the slightly less arid savanna belt to the south, known as the Sudan ....
13° 13th parallel north The 13th parallel north is a circle of latitude that is 13 degree true north of the Earth equator.Starting at the Prime Meridian and heading eastwards, the parallel 13? north passes through:...
11° 11th parallel north The 11th parallel north is a circle of latitude that is 11 degree true north of the Earth equator.Starting at the Prime Meridian and heading eastwards, the parallel 11? north passes through:...
10° 10th parallel north The 10th parallel north is a circle of latitude that is 10 degree true north of the Earth equator.A section of the border between Guinea and Sierra Leone is defined by the parallel....		Including Lake Volta Lake Volta Lake Volta is the largest reservoir by surface area in the world, lying in Ghana and covering almost 1 E9 m?. Its northernmost point is at the town of Yapei, and southernmost at the Akosombo Dam, 520 kilometers downstream....
5° N 5th parallel north The 5th parallel north is a circle of latitude that is 5 degree true north of the Earth equator.Starting at the Prime Meridian and heading eastwards, the parallel 5? north passes through:... 0° Equator The equator is the intersection of the Earth's surface with the Plane perpendicular to the Earth's rotation and containing the Earth's center of mass.... 5° S 5th parallel south The 5th parallel south is a circle of latitude that is 5 degree south of the Earth equator.Starting at the Prime Meridian and heading eastwards, the parallel 5? south passes through:... 10° 10th parallel south The 10th parallel south is a circle of latitude that is 10 degree south of the Earth equator.Part of the border between Brazil and Peru is defined by the parallel.... 15° 15th parallel south The 15th parallel south is a circle of latitude that is 15 degree south of the Earth equator.Starting at the Prime Meridian and heading eastwards, the parallel 15? south passes through:... 20° 20th parallel south The 20th parallel south is a circle of latitude that is 20 degree south of the Earth equator.Starting at the Prime Meridian and heading eastwards, the parallel 20? south passes through:... 25° 25th parallel south The 25th parallel south is a circle of latitude that is 25 degree south of the Earth equator, just south of the Tropic of Capricorn.Starting at the Prime Meridian and heading eastwards, the parallel 25? south passes through:... 30° 30th parallel south The 30th parallel south is a circle of latitude that is 30 degree south of the Earth equator.Starting at the Prime Meridian and heading eastwards, the parallel 30? south passes through:... 35° 35th parallel south The 35th parallel south is a circle of latitude that is 35 degree south of the Earth equator.Starting at the Prime Meridian and heading eastwards, the parallel 35? south passes through:... 40° 40th parallel south The 40th parallel south is a circle of latitude that is 40 degree south of the Earth equator.Starting at the Prime Meridian and heading eastwards, the parallel 40? south passes through:... 45° 45th parallel south The 45th parallel south is a circle of latitude that is 45 degree south of the Earth equator. The parallel is the line that marks the theoretical halfway point between the equator and the South Pole.... 50° 50th parallel south The 50th parallel south is a circle of latitude that is 50 degree south of the Earth equator.Starting at the Prime Meridian and heading eastwards, the parallel 50? south passes through:... 55° 55th parallel south The 55th parallel south is a circle of latitude that is 55 degree south of the Earth equator.Starting at the Prime Meridian and heading eastwards, the parallel 55? south passes through:...	Atlantic Ocean Atlantic Ocean The Atlantic Ocean is the second-largest of the world's oceanic divisions; with a total area of about 106.4 million square kilometres . It covers approximately one-fifth of the Earth's surface....
60° 60th parallel south The 60th parallel south is a circle of latitude that is 60 degree south of the Earth equator.The parallel marks the northern limit of the Southern Ocean....	Southern Ocean Southern Ocean The Southern Ocean, also known as the Great Southern Ocean, the Antarctic Ocean and the South Polar Ocean, comprises the southernmost waters of the World Ocean south of 60th parallel south latitude....
70° 70th parallel south The 70th parallel south is a circle of latitude that is 70 degree south of the Earth equator.The parallel passes through the Southern Ocean and Antarctica... 80° 80th parallel south The 80th parallel south is a circle of latitude that is 80 degree south of the Earth equator.It passes through Antarctica and Antarctic ice shelf.... 90° South Pole The South Pole, also known as the Geographic South Pole or Terrestrial South Pole, is one of the two points where the Earth's rotation intersects the surface....	Antarctica Antarctica Antarctica is Earth's southernmost continent, overlying the South Pole. It is situated in the Antarctica of the southern hemisphere, almost entirely south of the Antarctic Circle, and is surrounded by the Southern Ocean....	Queen Maud Land Queen Maud Land Queen Maud Land is an English translation of Dronning Maud Land, the official name in use by Norwegian authorities and British Antarctic Survey on the part of Antarctica claimed by Norway as a dependent territory, on 14 January 1939.... , claimed List of Antarctic territorial claims This is an alphabetical list of Antarctica territories and territorial claims. The Antarctic Treaty prohibits new claims from being made after 1961 as well as the expansion of existing claims, but does not suspend preexisting claims.... by

History

The Prime Meridian is ultimately arbitrary — a matter of convention — and various conventions have been used or advocated throughout history:

Washington, D.C.
Washington, D.C.

Washington, D.C. , formally the District of Columbia and commonly referred to as Washington, the District, or simply D.C., is the Capital of the United States, founded on July 16, 1790....
(77° 3' 2.3? W; see Washington meridian
Washington meridian

The Washington meridian was one of four Prime Meridians of the United States which passed through History of Washington, D.C.. The four which have been specified are:...
)
Philadelphia
Philadelphia, Pennsylvania

Philadelphia is the largest city in Pennsylvania and the List of United States cities by population city in the United States. It is the fifth-largest metropolitan area and fourth-largest urban area by population in the United States, the nation's fourth-largest consumer media market as ranked by the Nielsen Media Research, and the 49th-most...
(75° 10' 12? W)
El Hierro (Ferro)
El Hierro

El Hierro, nicknamed Isla del Meridiano , is a Spain island. It is the smallest and furthest south and west of the Canary Islands, in the Atlantic Ocean off the coast of Africa....
, Canary Islands (18° 03' W, later redefined as 17° 39' 46? W)
Lisbon
Lisbon

Lisbon is the Capital and largest city of Portugal. It is also the seat of the Lisbon and capital of the Lisbon region. Its municipalities of Portugal, which matches the city proper excluding the larger continuous conurbation, has a municipal population of 564,477 in , while the Lisbon Metropolitan Area in total has around 2.8 million inha...
(9° 07' 54.862? W)
Madrid
Madrid

Madrid is the Capital and largest city of Spain. It is the Largest cities of the European Union by population within city limits in the European Union after Greater London and Berlin, and its Madrid metropolitan area is the Largest urban areas of the European Union in the European Union after Paris aire urbaine, Greater London Urban Area, a...
(3° 41' 16.58? W)
Paris
Paris

Paris is the Capital of France and the country's largest city. It is situated on the river Seine, in northern France, at the heart of the ?le-de-France Regions of France ....
(2° 20' 14.025? E; see Paris Meridian
Paris Meridian

The Paris Meridian is a Meridian running through the Paris Observatory in Paris, France?now longitude 2?20'14.025? east. It was a long-standing rival to Greenwich as the prime meridian of the world, as was the Antwerp meridian in Flanders....
)
Brussels
Brussels

Brussels , officially the Brussels Capital-Region, is the de facto capital city of the European Union and the largest urban area in Belgium....
(4° 22' 4.71? E)
Berne
Berne

The city of Berne or Bern is the Bundesstadt of Switzerland and, with 128,041 people , the fifth most populous city in Switzerland ....
(7° 26' 22.5? E)
Pisa
Pisa

Pisa is a city in Tuscany, central Italy, on the right bank of the mouth of the Arno River on the Ligurian Sea. It is the capital city of the Province of Pisa....
, Italy
Italy

Italy , officially the Italian Republic , is a country located on the Italian Peninsula in Southern Europe and on the two largest islands in the Mediterranean Sea, Sicily and Sardinia....
(10°24' E)
Oslo (Kristiania)
Oslo

is the Capital and largest List of cities in Norway in Norway.Metropolitan Oslo or the Greater Oslo Region makes up the third largest urban area in Scandinavia after Metropolitan Stockholm and Metropolitan Copenhagen....
(10° 43' 22.5? E)
Rome
Rome

Rome is the capital city of Italy and Lazio, and is Italy's largest and most populous city, with 2,724,347 residents in an urban area of some ....
(meridian of Mount Mario 12° 27' 08.4? E)
Copenhagen
Copenhagen

Copenhagen is the capital and largest city of Denmark, with an urban area with a population of 1,153,615 . Copenhagen is situated on the Islands of Zealand and Amager....
(12° 34' 32.25? E; Rundetårn
Rundetårn

File:Hafnia Hodierna Tab XCII Trinitatis Kirke.jpgRundet?rn is a 17th century tower located in Copenhagen, Denmark. The tower is part of the Trinitatis complex, which was built to provide the scholars of the time with an astronomical observatory, a student church and a university library....
)
Stockholm
Stockholm

is the capital and largest city of Sweden. It is the site of the national Swedish Government of Sweden, the Parliament of Sweden, and the official residence of the Swedish Monarchy of Sweden....
(at the observatory, 18° 3' 29.8? E)
Warsaw
Warsaw

Warsaw is the Capital and World's largest cities of Poland. It is located on the Vistula River roughly from both the Baltic Sea coast and the Carpathian Mountains....
(21° 00’ 42” E; see Warsaw meridian
Warsaw meridian

The Warsaw meridian is a meridian running through Warsaw. The local mean time at the meridian was known as Warsaw mean time, and was, since early nineteenth century, commonly used for timekeeping purposes in the lands of the former Polish-Lithuanian Commonwealth....
)
Oradea
Oradea

Oradea is the capital city of Bihor County, in Crisana, Romania. The city proper has a population of 206,614 census; this does not include areas from the metropolitan area, outside the municipality; they bring the total urban area population to approximately 240,000....
, Romania
Romania

Romania is a country located in Southeastern Europe Central Europe, North of the Balkan Peninsula, on the Lower Danube, within and outside the Carpathian Mountains, bordering on the Black Sea....
(21° 55' 16? E)
Alexandria
Alexandria

Alexandria , with a population of 4.1 million, is the second-largest city in Egypt, and is the country's largest seaport, serving about 80% of Egypt's imports and exports....
(29° 53' E)
Saint Petersburg
Saint Petersburg

Saint Petersburg is a types of inhabited localities in Russia and a federal subjects of Russia of Russia located on the Neva River at the head of the Gulf of Finland on the Baltic Sea....
(Pulkovo meridian, 30° 19' 42.09? E)
Great Pyramid of Giza
Great Pyramid of Giza

The Great Pyramid of Giza, also called Khufu's Pyramid or the Pyramid of Khufu, and Pyramid of Cheops, is the oldest and largest of the three Egyptian pyramidss in the Giza Necropolis bordering what is now Cairo , Egypt, and is the only remaining member of the Seven Wonders of the Ancient World....
(31° 8' 3.69? E, 1884)
Jerusalem
Jerusalem

Jerusalem is the capital of Israel and its List of Israeli cities in both population and area, with a population of 747,600 residents over an area of if Positions on Jerusalem East Jerusalem is included....
(35° 13' 46? E for the large dome of the Church of the Holy Sepulchre
Church of the Holy Sepulchre

The Church of the Holy Sepulchre , also called the Church of the Resurrection, by Eastern Christianitys, is a Christianity Church within the walled Old City of Jerusalem....
)
Mecca
Mecca

Mecca , also spelled Makkah , Makka is a city in Saudi Arabia. Home to the Masjid al-Haram, it is the holy city in Islam and plays an important role in the faith....
(39° 49' E)
Approximately 59° east of Greenwich
Ujjain
Ujjain

Ujjain , is an ancient city of Malwa in central India on the eastern bank of the Kshipra River In ancient times the city was called Ujjayini....
(75° 47' E) Used in Indian astronomy and calendars.

The Greenwich Meridian, based at the Royal Observatory, Greenwich

Royal Observatory, Greenwich

The Royal Observatory, Greenwich was commissioned in 1675 by Charles II of England, with the foundation stone being laid on 10 August. At this time the king also created the position of Astronomer Royal , to serve as the director of the observatory and to "apply himself with the most exact care and diligence to the rectifying of the tab...
, was established by Sir George Airy

George Biddell Airy

Sir George Biddell Airy Fellow of the Royal Society was an England mathematician and astronomer, Astronomer Royal from 1835 to 1881. His many achievements include work on planetary orbits, measuring the mean density of the Earth, a method of solution of two-dimensional problems in solid mechanics and, in his role as Astronomer Royal, establi...
in 1851. By 1884, over two-thirds of all ships and tonnage used it as the reference meridian on their maps. In October of that year, at the behest of U.S. President

President of the United States

The President of the United States is the head of state and head of government of the United States and is the highest political official in the United States by influence and recognition....
Chester A. Arthur

Chester A. Arthur

Chester Alan Arthur was an Politics of the United States who served as the List of Presidents of the United States President of the United States....
, 41 delegates from 25 nations met in Washington, D.C.

Washington, D.C.

Washington, D.C. , formally the District of Columbia and commonly referred to as Washington, the District, or simply D.C., is the Capital of the United States, founded on July 16, 1790....
, USA, for the International Meridian Conference

International Meridian Conference

The International Meridian Conference was a meeting held in October 1884 in Washington, D.C. in the United States to determine the Prime Meridian of the world....
. This conference selected the Greenwich Meridian as the official Prime Meridian due to its popularity. However, France abstained from the vote and French maps continued to use the Paris Meridian

Paris Meridian

The Paris Meridian is a Meridian running through the Paris Observatory in Paris, France?now longitude 2?20'14.025? east. It was a long-standing rival to Greenwich as the prime meridian of the world, as was the Antwerp meridian in Flanders....
for several decades.

The Greenwich Meridian is now marked at night by a laser

Laser

A laser is a device that emits light through a process called stimulated emission. The term laser is an acronym for light amplification by stimulated emission of radiation....
beam emitted from the observatory.

IERS Reference Meridian

The International Earth Rotation and Reference Systems Service

International Earth Rotation and Reference Systems Service

The International Earth Rotation and Reference Systems Service , formerly the International Earth Rotation Service, is the body responsible for maintaining global time and Frame of reference standards, notably through its Earth Orientation Parameter and International Celestial Reference System groups....
(IERS) maintains the IERS Reference Meridian (IRM), also called the International Reference Meridian, which is the reference meridian (prime meridian, 0° longitude) of the Global Positioning System

Global Positioning System

The Global Positioning System is a global navigation satellite system developed by the United States Department of Defense and managed by the United States Air Force 50th Space Wing....
operated by the United States Department of Defense

United States Department of Defense

The United States Department of Defense is the federal department charged with coordinating and supervising all agencies and functions of the government relating directly to national security and the Military of the United States....
, and is the reference meridian in WGS84 and in its formal versions, the ideal International Terrestrial Reference System

International Terrestrial Reference System

The International Terrestrial Reference System describes procedures for creating reference frames suitable for use with measurements on or near the Earth's surface....
(ITRS) and its realization, the International Terrestrial Reference Frame (ITRF). It is 5.31? east of Airy's transit circle or 102.5 metres (336.3 feet) at the latitude

Latitude

Latitude, usually denoted symbolically by the Greek letter phi gives the location of a place on Earth north or south of the equator. Lines of Latitude are the horizontal lines shown running east-to-west on maps ....
of the Royal Observatory, Greenwich. This shift is a legacy of the first satellite navigation system, the Doppler

Doppler effect

The Doppler effect , named after Austrian physicist Christian Doppler who proposed it in 1842, is the change in frequency and wavelength of a wave for an observer moving relative to the source of the waves....
based TRANSIT

Transit (satellite)

The TRANSIT system, also known as NAVSAT , was the first satellite navigation system to be used operationally. The system was primarily used by the US Navy to provide accurate location information to ballistic missile submarines, and was also used as a general navigation system by the Navy, as well as hydrographic and geodetic surveyi...
system developed by the Applied Physics Laboratory

Applied Physics Laboratory

The Johns Hopkins University Applied Physics Laboratory , located in Laurel, Maryland, is a not-for-profit, University_Affiliated_Research_Center employing 4,150 people....
of Johns Hopkins University

Johns Hopkins University

The Johns Hopkins University, commonly referred to as Hopkins or JHU, is a private university research university located in Baltimore, Maryland, Maryland, United States....
in Howard County, Maryland

Howard County, Maryland

Howard County is a county located in the central part of the U.S. state of Maryland, between Baltimore, Maryland and Washington, D.C.. It is considered part of the Baltimore-Washington Metropolitan Area....
. This was the location of its first ground station, so the surveyed coordinates of that ground station in the North American Datum

North American Datum

The North American Datum is the official datum used for the primary Geodesy network in North America.In the fields of cartography and land-use there are currently two North American Datums in use: the North American Datum of 1927 and the North American Datum of 1983 ....
1927 (NAD27), a non-Earth centered ellipsoid, became its coordinates in an Earth-centered ellipsoid, such as the World Geodetic System

World Geodetic System

The World Geodetic System is a standard for use in cartography, geodesy, and navigation. It comprises a standard Cartesian coordinates for the Earth, a standard spheroid reference surface for raw altitude data, and a gravitation equipotential surface that defines the "nominal sea level"....
. This caused the coordinates of any other location on an Earth-centered ellipsoid to shift, especially those far away. When the antenna of a TRANSIT ground station was mounted directly above Airy's transit instrument in June 1969, its longitude on an Earth-centered ellipsoid was 5.64? west of TRANSIT's reference meridian. Further improvement in gravitational models, such as the Earth Geopotential Model 1996 (EGM96

EGM96

EGM96 is a geopotential model of the Earth consisting of spherical harmonic coefficients complete to degree and order 360. It is a composite solution, consisting of: a combination solution to degree and order 70, a block diagonal solution from degree 171 to 621, and the quadrature solution at degree 360....
), and a dramatic increase in the number of ground stations from only four to over 500, as well as the use of time based GPS caused a small additional shift before it reached its present position.

The International Hydrographic Organization

International Hydrographic Organization

The International Hydrographic Organization was originally established in 1921 as the International Hydrographic Bureau . The present name was adopted in 1970 as a result of a revised international agreement among member nations....
adopted an early version in 1983 for all nautical charts. It was adopted for air navigation by the International Civil Aviation Organization

International Civil Aviation Organization

The International Civil Aviation Organization , an agency of the United Nations, codifies the principles and techniques of international air navigation and fosters the planning and development of international scheduled air transport to ensure safe and orderly growth....
on 3 March 1989. Because tectonic plate

Tectonic Plate

#REDIRECT Plate tectonics...
s slowly move over the surface of the Earth, most countries have adopted a version of the IRM for their maps that is fixed relative to their own tectonic plate as it existed at the beginning of a specific year, such as 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.

However, the IRM is not fixed to any point on Earth. Instead, all points on the European portion of the Eurasian plate, including the Royal Observatory, are slowly moving northeast about 2.5 cm per year relative to it. This IRM is the weighted average in the least squares

Least squares

The method of least squares or ordinary least squares is used to solve overdetermined systems. Least squares is often applied in statistical contexts, particularly regression analysis....
sense of the reference meridians of the hundreds of ground stations contributing to the IERS network, including GPS stations, Satellite Laser Ranging

Satellite laser ranging

In satellite laser ranging a global network of observation stations measure the round trip time of flight of ultrashort pulses of light to satellites equipped with retroreflectors....
(SLR) stations, Lunar Laser Ranging (LLR) stations, and the highly accurate Very Long Baseline Interferometry

Very Long Baseline Interferometry

Very Long Baseline Interferometry is a type of astronomical interferometer used in radio astronomy. It allows observations of an object that are made simultaneously by many telescopes to be combined, emulating a telescope with a size equal to the maximum separation between the telescopes....
(VLBI) stations. The coordinates of all of these stations are adjusted annually until there is no net rotation relative to the major tectonic plates. If Earth had only two hemispherical plates moving relative to each other around any axis from that intersecting their centres to one intersecting their junction, the longitudes (around any other rotation axis) of any two stations diametrically opposite each other must move in opposite directions by the same amount.

Universal Time

Universal Time

Universal Time is a timescale based on the rotation of the Earth. It is a modern continuation of Greenwich Mean Time , i.e., the mean solar time on the meridian of Royal Observatory, Greenwich, and GMT is sometimes used loosely as a synonym for UTC....
is notionally based on the WGS84 meridian. However, the standard international time UTC

Coordinated Universal Time

Coordinated Universal Time is a time standard based on International Atomic Time with leap seconds added at irregular intervals to compensate for the Earth's slowing rotation....
can differ from the mean observed time on the meridian by up to 0.9 second (equivalent to about 260 metres at Greenwich), because of changes in the Earth's rotation. Leap second

Leap second

A leap second is a plus or minus one-second adjustment to the Coordinated Universal Time time scale that keeps it close to Solar time. UTC, which is used as the basis for official time-of-day radio broadcasts for civil time, is maintained using extremely precise atomic clocks....
s are inserted periodically to keep UTC close to Earth's angular position relative to the Sun — mean solar time.

United Kingdom Ordnance Survey Zero Meridian

The zero meridian used by the Ordnance Survey

Ordnance Survey

Ordnance Survey is an executive agency of the United Kingdom government. It is the national mapping agency for Great Britain, and one of the world's largest producers of maps....
(OSGB36 datum) is about six metres to the west of the Airy meridian marked at Greenwich. When the first Ordnance Survey map was published in 1801, the official Prime Meridian of Great Britain was the one established by the third Astronomer Royal

Astronomer Royal

Astronomer Royal is a senior post in the Royal Household of the Monarch of the United Kingdom. There are two officers, the senior being the Astronomer Royal dating from 22 June 1675; the second is the Astronomer Royal for Scotland dating from 1834....
, James Bradley

James Bradley

James Bradley was an English astronomer, Astronomer Royal from 1742. He is best known for discovering the aberration of light while attempting to detect stellar parallax....
. When Airy's new Prime Meridian superseded it fifty years later, the Ordnance Survey simply continued to use Bradley's.

Other planetary bodies

The prime meridians of the following bodies in the Solar System

Solar System

The Solar System consists of the Sun and those Astronomical object bound to it by gravity: the eight planets and five dwarf planets, their 173 known Natural satellite, and billions of Small Solar System body....
have been defined:

The prime meridian of the Moon
Moon

The Moon is Earth's only natural satellite and the List of natural satellites by diameter satellite in the Solar System. The average centre-to-centre distance from the Earth to the Moon is km, about thirty times the diameter of the Earth....
lies directly in the middle of the face of the moon visible from Earth and passes near the crater Bruce
Bruce (crater)

Bruce is a small moon impact crater located in the Sinus Medii. It lies to the west-northwest of the irregular crater Rhaeticus , and just to the west of the even smaller Blagg ....
.
The prime meridian of Mars
MARS

In cryptography, MARS is a block cipher that was IBM's submission to the Advanced Encryption Standard process. MARS was selected as an AES finalist in August 1999, after the AES2 conference in March 1999, where it was voted as the fifth and last finalist algorithm....
is defined by the crater Airy-0
Airy-0

Airy-0 is a crater on Mars whose location defines the position of the prime meridian of that planet. Airy-0 is about 0.5 kilometers across and lies within the larger crater Airy in the region Sinus Meridiani....
.
The prime meridian of Venus
Venus

Venus is the second-closest planet to the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus , the Roman mythology goddess of love....
passes through the center of a radar-bright spot on the center of the oval feature Eve, which lies to the south of Alpha Regio.

External links

, prime meridian at MSN maps

Prime Meridian

Geography

History

IERS Reference Meridian

United Kingdom Ordnance Survey Zero Meridian

Other planetary bodies

See also

External links