Prime Meridian

Prime Meridian

Overview
The Prime Meridian is the meridian
Meridian (geography)
A meridian is an imaginary line on the Earth's surface from the North Pole to the South Pole that connects all locations along it with a given longitude. The position of a point along the meridian is given by its latitude. Each meridian is perpendicular to all circles of latitude...

 (line of longitude
Longitude
Longitude is a geographic coordinate that specifies the east-west position of a point on the Earth's surface. It is an angular measurement, usually expressed in degrees, minutes and seconds, and denoted by the Greek letter lambda ....

) at which the longitude is defined to be 0°.

The Prime Meridian and its opposite the 180th meridian
180th meridian
The 180th meridian or antimeridian is the meridian which is 180° east or west of the Prime Meridian passing through the Royal Observatory, Greenwich. It is common to both east longitude and west longitude. It is used as the basis for the International Date Line because it for the most part passes...

 (at 180° longitude), which the International Date Line
International Date Line
The International Date Line is a generally north-south imaginary line on the surface of the Earth, passing through the middle of the Pacific Ocean, that designates the place where each calendar day begins...

 generally follows, form a great circle
Great circle
A great circle, also known as a Riemannian circle, of a sphere is the intersection of the sphere and a plane which passes through the center point of the sphere, as opposed to a general circle of a sphere where the plane is not required to pass through the center...

 that divides the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

 into the Eastern
Eastern Hemisphere
The Eastern Hemisphere, also Eastern hemisphere or eastern hemisphere, is a geographical term for the half of the Earth that is east of the Prime Meridian and west of 180° longitude. It is also used to refer to Europe, Asia, Africa, and Australasia, vis-à-vis the Western Hemisphere, which includes...

 and Western
Western Hemisphere
The Western Hemisphere or western hemisphere is mainly used as a geographical term for the half of the Earth that lies west of the Prime Meridian and east of the Antimeridian , the other half being called the Eastern Hemisphere.In this sense, the western hemisphere consists of the western portions...

 Hemispheres.

An international conference in 1884 decided the modern Prime Meridian passes through the Royal Observatory, Greenwich
Royal Observatory, Greenwich
The Royal Observatory, Greenwich , in London, England played a major role in the history of astronomy and navigation, and is best known as the location of the prime meridian...

 in southeast London
London
London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...

, United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

, known as the International Meridian or Greenwich Meridian, although the Prime Meridian is ultimately arbitrary unlike the parallels of latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...

, which are defined by the rotational axis of the Earth with the Poles
Geographical pole
A geographical pole is either of the two points—the north pole and the south pole—on the surface of a rotating planet where the axis of rotation meets the surface of the body...

 at 90° and the Equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....

 at 0°.

Historically, various meridians have been used, including four different ones through Greenwich.


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 its 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 axis of rotation intersects its surface. It is the southernmost point on the surface of the Earth and lies on the opposite side of the Earth from the North Pole...

, the Prime Meridian passes through:




The Prime Meridian is ultimately arbitrary—a matter of convention—and various conventions have been used or advocated in different regions and 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. On July 16, 1790, the United States Congress approved the creation of a permanent national capital as permitted by the U.S. Constitution....

     (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 Washington, D.C.. The four which have been specified are:# through the Capitol# through the White House# through the old Naval Observatory...

  • Philadelphia
    Philadelphia, Pennsylvania
    Philadelphia is the largest city in the Commonwealth of Pennsylvania and the county seat of Philadelphia County, with which it is coterminous. The city is located in the Northeastern United States along the Delaware and Schuylkill rivers. It is the fifth-most-populous city in the United States,...

     (75° 10' 12” W)
  • Rio de Janeiro
    Rio de Janeiro
    Rio de Janeiro , commonly referred to simply as Rio, is the capital city of the State of Rio de Janeiro, the second largest city of Brazil, and the third largest metropolitan area and agglomeration in South America, boasting approximately 6.3 million people within the city proper, making it the 6th...

     (43° 10' 19” W)
  • El Hierro (Ferro)
    El Hierro
    El Hierro, nicknamed Isla del Meridiano , is the smallest and farthest south and west of the Canary Islands , in the Atlantic Ocean off the coast of Africa, with a population of 10,162 .- Name :The name El Hierro, although phonetically identical to the Spanish word for 'iron', is generally thought...

    , Canary Islands (18° 03' W, later redefined as 17° 39' 46”? W)
  • Lisbon
    Lisbon
    Lisbon is the capital city and largest city of Portugal with a population of 545,245 within its administrative limits on a land area of . The urban area of Lisbon extends beyond the administrative city limits with a population of 3 million on an area of , making it the 9th most populous urban...

     (9° 07' 54.862” W)
  • Madrid
    Madrid
    Madrid is the capital and largest city of Spain. The population of the city is roughly 3.3 million and the entire population of the Madrid metropolitan area is calculated to be 6.271 million. It is the third largest city in the European Union, after London and Berlin, and its metropolitan...

     (3° 41' 16.58” W)
  • Paris
    Paris
    Paris is the capital and largest city in France, situated on the river Seine, in northern France, at the heart of the Île-de-France region...

     (2° 20' 14.025” E), see Paris Meridian
    Paris Meridian
    The Paris Meridian is a meridian line 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 Meridian of Antwerp in Antwerp, Belgium....

  • Brussels
    Brussels
    Brussels , officially the Brussels Region or Brussels-Capital Region , is the capital of Belgium and the de facto capital of the European Union...

     (4° 22' 4.71” E)
  • Antwerp (4° 24' E), used by Mercator, see Meridian of Antwerp
    Meridian of Antwerp
    The Meridian of Antwerp is an analog to the Paris Meridian and Prime Meridian, running through the city of Antwerp, in Flanders, Belgium, and forming the 0° longitude upon which some Belgian maps were based...

  • Bern (7° 26' 22.5” E)
  • Pisa
    Pisa
    Pisa is a city in Tuscany, Central Italy, on the right bank of the mouth of the River Arno on the Tyrrhenian Sea. It is the capital city of the Province of Pisa...

    , Italy
    Italy
    Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...

     (10°24' E)
  • Oslo (Kristiania)
    Oslo
    Oslo is a municipality, as well as the capital and most populous city in Norway. As a municipality , it was established on 1 January 1838. Founded around 1048 by King Harald III of Norway, the city was largely destroyed by fire in 1624. The city was moved under the reign of Denmark–Norway's King...

     (10° 43' 22.5” E)
  • Rome
    Rome
    Rome is the capital of Italy and the country's largest and most populated city and comune, with over 2.7 million residents in . The city is located in the central-western portion of the Italian Peninsula, on the Tiber River within the Lazio region of Italy.Rome's history spans two and a half...

     (12° 27' 08.4” E), meridian of Monte Mario
    Monte Mario
    -External links :* * *...

  • Copenhagen
    Copenhagen
    Copenhagen is the capital and largest city of Denmark, with an urban population of 1,199,224 and a metropolitan population of 1,930,260 . With the completion of the transnational Øresund Bridge in 2000, Copenhagen has become the centre of the increasingly integrating Øresund Region...

     (12° 34' 32.25” E) Rundetårn
    Rundetårn
    The Rundetårn is a 17th-century tower located in central Copenhagen, Denmark. One of the many architectural projects of Christian IV, it was built as an astronomical observatory...

  • Stockholm
    Stockholm
    Stockholm is the capital and the largest city of Sweden and constitutes the most populated urban area in Scandinavia. Stockholm is the most populous city in Sweden, with a population of 851,155 in the municipality , 1.37 million in the urban area , and around 2.1 million in the metropolitan area...

     (18° 3' 29.8” E), at the observatory
    Stockholm Observatory
    The Stockholm Observatory is an astronomical institution in Stockholm, Sweden, founded in the 18th century and today part of Stockholm University...

  • Warsaw
    Warsaw
    Warsaw is the capital and largest city of Poland. It is located on the Vistula River, roughly from the Baltic Sea and from the Carpathian Mountains. Its population in 2010 was estimated at 1,716,855 residents with a greater metropolitan area of 2,631,902 residents, making Warsaw the 10th most...

     (21° 00’ 42” E), see Warsaw meridian
    Warsaw meridian
    The Warsaw meridian is a meridian line running through Warsaw. The local mean time at the meridian was known as Warsaw mean time. It corresponds to an offset from UTC of +01:24....

  • Oradea
    Oradea
    Oradea is the capital city of Bihor County, in the Crișana region of north-western Romania. The city has a population of 204,477, according to the 2009 estimates. The wider Oradea metropolitan area has a total population of 245,832.-Geography:...

    , Romania
    Romania
    Romania is a country located at the crossroads of Central and Southeastern Europe, on the Lower Danube, within and outside the Carpathian arch, bordering on the Black Sea...

     (21° 55' 16” E)
  • Alexandria
    Alexandria
    Alexandria is the second-largest city of Egypt, with a population of 4.1 million, extending about along the coast of the Mediterranean Sea in the north central part of the country; it is also the largest city lying directly on the Mediterranean coast. It is Egypt's largest seaport, serving...

     (29° 53' E)
  • Saint Petersburg
    Saint Petersburg
    Saint Petersburg is a city and a federal subject of Russia located on the Neva River at the head of the Gulf of Finland on the Baltic Sea...

     (30° 19' 42.09” E), Pulkovo meridian
  • Great Pyramid of Giza
    Great Pyramid of Giza
    The Great Pyramid of Giza is the oldest and largest of the three pyramids in the Giza Necropolis bordering what is now El Giza, Egypt. It is the oldest of the Seven Wonders of the Ancient World, and the only one to remain largely intact...

     (31° 8' 3.69” E), 1884
  • Jerusalem (35° 13' 47.1” E), for the small 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 Christians, is a church within the walled Old City of Jerusalem. It is a few steps away from the Muristan....

  • Mecca
    Mecca
    Mecca is a city in the Hijaz and the capital of Makkah province in Saudi Arabia. The city is located inland from Jeddah in a narrow valley at a height of above sea level...

     (39° 49′ 34″ E), see Mecca Time
    Mecca Time
    Mecca Time is a time standard that uses the line of longitude that goes through Mecca, Saudi Arabia as its Prime Meridian. Its proposed use as a global standard is based on the claim that the city is the true center of the Earth and thus should become the basis of the world's timezones...

  • Approximately 59° east of Greenwich
  • Ujjain
    Ujjain
    Ujjain , is an ancient city of Malwa region in central India, on the eastern bank of the Kshipra River , today part of the state of Madhya Pradesh. It is the administrative centre of Ujjain District and Ujjain Division.In ancient times the city was called Ujjayini...

     (75° 47' E), Used from 4th century CE Indian astronomy and calendars.
  • Kyoto
    Kyoto
    is a city in the central part of the island of Honshū, Japan. It has a population close to 1.5 million. Formerly the imperial capital of Japan, it is now the capital of Kyoto Prefecture, as well as a major part of the Osaka-Kobe-Kyoto metropolitan area.-History:...

     (135° 74' E), Used in 18th and 19th (officially 1779-1871) century Japanese maps.
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Unanswered Questions
Encyclopedia
The Prime Meridian is the meridian
Meridian (geography)
A meridian is an imaginary line on the Earth's surface from the North Pole to the South Pole that connects all locations along it with a given longitude. The position of a point along the meridian is given by its latitude. Each meridian is perpendicular to all circles of latitude...

 (line of longitude
Longitude
Longitude is a geographic coordinate that specifies the east-west position of a point on the Earth's surface. It is an angular measurement, usually expressed in degrees, minutes and seconds, and denoted by the Greek letter lambda ....

) at which the longitude is defined to be 0°.

The Prime Meridian and its opposite the 180th meridian
180th meridian
The 180th meridian or antimeridian is the meridian which is 180° east or west of the Prime Meridian passing through the Royal Observatory, Greenwich. It is common to both east longitude and west longitude. It is used as the basis for the International Date Line because it for the most part passes...

 (at 180° longitude), which the International Date Line
International Date Line
The International Date Line is a generally north-south imaginary line on the surface of the Earth, passing through the middle of the Pacific Ocean, that designates the place where each calendar day begins...

 generally follows, form a great circle
Great circle
A great circle, also known as a Riemannian circle, of a sphere is the intersection of the sphere and a plane which passes through the center point of the sphere, as opposed to a general circle of a sphere where the plane is not required to pass through the center...

 that divides the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

 into the Eastern
Eastern Hemisphere
The Eastern Hemisphere, also Eastern hemisphere or eastern hemisphere, is a geographical term for the half of the Earth that is east of the Prime Meridian and west of 180° longitude. It is also used to refer to Europe, Asia, Africa, and Australasia, vis-à-vis the Western Hemisphere, which includes...

 and Western
Western Hemisphere
The Western Hemisphere or western hemisphere is mainly used as a geographical term for the half of the Earth that lies west of the Prime Meridian and east of the Antimeridian , the other half being called the Eastern Hemisphere.In this sense, the western hemisphere consists of the western portions...

 Hemispheres.

An international conference in 1884 decided the modern Prime Meridian passes through the Royal Observatory, Greenwich
Royal Observatory, Greenwich
The Royal Observatory, Greenwich , in London, England played a major role in the history of astronomy and navigation, and is best known as the location of the prime meridian...

 in southeast London
London
London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...

, United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

, known as the International Meridian or Greenwich Meridian, although the Prime Meridian is ultimately arbitrary unlike the parallels of latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...

, which are defined by the rotational axis of the Earth with the Poles
Geographical pole
A geographical pole is either of the two points—the north pole and the south pole—on the surface of a rotating planet where the axis of rotation meets the surface of the body...

 at 90° and the Equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....

 at 0°.

Historically, various meridians have been used, including four different ones through Greenwich.

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 its 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 axis of rotation intersects its surface. It is the southernmost point on the surface of the Earth and lies on the opposite side of the Earth from the North Pole...

, the Prime Meridian passes through:
Co-ordinates
(approximate)
Country, territory or sea Notes
90°0′N 0°0′E Arctic Ocean
Arctic Ocean
The Arctic Ocean, located in the Northern Hemisphere and mostly in the Arctic north polar region, is the smallest and shallowest of the world's five major oceanic divisions...

81°39′N 0°0′E Greenland Sea
Greenland Sea
The Greenland Sea is a body of water that borders Greenland to the west, the Svalbard archipelago to the east, Fram Strait and the Arctic Ocean to the north, and the Norwegian Sea and Iceland to the south. The Greenland Sea is often defined as part of the Arctic Ocean, sometimes as part of the...

72°53′N 0°0′E Norwegian Sea
Norwegian Sea
The Norwegian Sea is a marginal sea in the North Atlantic Ocean, northwest of Norway. It is located between the North Sea and the Greenland Sea and adjoins the North Atlantic Ocean to the west and the Barents Sea to the northeast. In the southwest, it is separated from the Atlantic Ocean by a...

61°0′N 0°0′E North Sea
North Sea
In the southwest, beyond the Straits of Dover, the North Sea becomes the English Channel connecting to the Atlantic Ocean. In the east, it connects to the Baltic Sea via the Skagerrak and Kattegat, narrow straits that separate Denmark from Norway and Sweden respectively...

53°45′N 0°0′E The northernmost land on this meridian is near Tunstall in East Riding,Yorkshire
Tunstall, East Riding of Yorkshire
Tunstall is a village in the East Riding of Yorkshire, England, in an area known as Holderness. It is situated approximately north west of the town of Withernsea, near to the North Sea coast...

.
The southernmost land in the UK is Peacehaven
Peacehaven
Peacehaven is a town and civil parish in the Lewes district of East Sussex, England. It is located above the chalk cliffs of the South Downs approximately six miles east of Brighton city centre, on the A259 road...

, East Sussex
East Sussex
East Sussex is a county in South East England. It is bordered by the counties of Kent, Surrey and West Sussex, and to the south by the English Channel.-History:...

.
50°47′N 0°0′E English Channel
English Channel
The English Channel , often referred to simply as the Channel, is an arm of the Atlantic Ocean that separates southern 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 in the Strait of Dover...

49°19′N 0°0′E The northernmost point on this meridian is in Villers-sur-Mer
Villers-sur-Mer
-Places of interest:Villers-sur-Mer is known for the large topiary dinosaurs facing the sea from the garden of the office of tourism. In certain years, a baby dinosaur is added to the garden....

, Calvados
Calvados
The French department of Calvados is part of the region of Basse-Normandie in Normandy. It takes its name from a cluster of rocks off the English Channel coast...

.
The southernmost point is near Gavarnie
Gavarnie
Gavarnie is a commune in the Hautes-Pyrénées department in south-western France.-See also:* Cirque de Gavarnie* Gavarnie Falls*Communes of the Hautes-Pyrénées department-References:*...

.
42°41′N 0°0′E Passing just west of Monte Perdido
Monte Perdido
Monte Perdido is the third highest mountain in the Pyrenees. The summit of Monte Perdido , located in Spain, lies hidden from France by the seemingly impenetrable peaks of the Cirques of Gavarnie and Estaubé. It is in the north of Huesca province...

, in the Pyrenees
Pyrenees
The Pyrenees is a range of mountains in southwest Europe that forms a natural border between France and Spain...

39°56′N 0°0′E Mediterranean Sea
Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...

Gulf of Valencia
Gulf of Valencia
The Gulf of Valencia , is a gulf or inlet of the western Mediterranean Sea, on the eastern coast of Spain. Its limits are the Cap de la Nau headland in the south, while the northern limit is diffuse: for some it is the Cape of Vinaròs; and for others it is the Ebre Delta. When the Cape of Vinaròs...

38°52′N 0°0′E
38°38′N 0°0′E Mediterranean Sea
Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...

35°50′N 0°0′E
21°50′N 0°0′E
14°59′N 0°0′E
11°6′N 0°0′E For about 600 m
11°6′N 0°0′E For about 16 km
10°57′N 0°0′E For about 39 km
10°36′N 0°0′E Passing through Lake Volta
Lake Volta
Lake Volta is the largest reservoir by surface area in the world, and the fourth largest one by water volume. It is located completely within the country of Ghana, and it has a surface area of about 8,502 km² . Lake Volta lies along the Greenwich Meridian, and just six degrees of latitude...

 at 7°48′N 0°0′E
5°37′N 0°0′E Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...

Passing through the Equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....

 at 0°0′N 0°0′E
60°0′S 0°0′E Southern Ocean
Southern Ocean
The Southern Ocean comprises the southernmost waters of the World Ocean, generally taken to be south of 60°S latitude and encircling Antarctica. It is usually regarded as the fourth-largest of the five principal oceanic divisions...

68°54′S 0°0′E Antarctica Queen Maud Land
Queen Maud Land
Queen Maud Land is a c. 2.7 million-square-kilometre region of Antarctica claimed as a dependent territory by Norway. The territory lies between 20° west and 45° east, between the British Antarctic Territory to the west and the Australian Antarctic Territory to the east. The latitudinal...

, claimed by

History




The Prime Meridian is ultimately arbitrary—a matter of convention—and various conventions have been used or advocated in different regions and 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. On July 16, 1790, the United States Congress approved the creation of a permanent national capital as permitted by the U.S. Constitution....

     (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 Washington, D.C.. The four which have been specified are:# through the Capitol# through the White House# through the old Naval Observatory...

  • Philadelphia
    Philadelphia, Pennsylvania
    Philadelphia is the largest city in the Commonwealth of Pennsylvania and the county seat of Philadelphia County, with which it is coterminous. The city is located in the Northeastern United States along the Delaware and Schuylkill rivers. It is the fifth-most-populous city in the United States,...

     (75° 10' 12” W)
  • Rio de Janeiro
    Rio de Janeiro
    Rio de Janeiro , commonly referred to simply as Rio, is the capital city of the State of Rio de Janeiro, the second largest city of Brazil, and the third largest metropolitan area and agglomeration in South America, boasting approximately 6.3 million people within the city proper, making it the 6th...

     (43° 10' 19” W)
  • El Hierro (Ferro)
    El Hierro
    El Hierro, nicknamed Isla del Meridiano , is the smallest and farthest south and west of the Canary Islands , in the Atlantic Ocean off the coast of Africa, with a population of 10,162 .- Name :The name El Hierro, although phonetically identical to the Spanish word for 'iron', is generally thought...

    , Canary Islands (18° 03' W, later redefined as 17° 39' 46”? W)
  • Lisbon
    Lisbon
    Lisbon is the capital city and largest city of Portugal with a population of 545,245 within its administrative limits on a land area of . The urban area of Lisbon extends beyond the administrative city limits with a population of 3 million on an area of , making it the 9th most populous urban...

     (9° 07' 54.862” W)
  • Madrid
    Madrid
    Madrid is the capital and largest city of Spain. The population of the city is roughly 3.3 million and the entire population of the Madrid metropolitan area is calculated to be 6.271 million. It is the third largest city in the European Union, after London and Berlin, and its metropolitan...

     (3° 41' 16.58” W)
  • Paris
    Paris
    Paris is the capital and largest city in France, situated on the river Seine, in northern France, at the heart of the Île-de-France region...

     (2° 20' 14.025” E), see Paris Meridian
    Paris Meridian
    The Paris Meridian is a meridian line 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 Meridian of Antwerp in Antwerp, Belgium....

  • Brussels
    Brussels
    Brussels , officially the Brussels Region or Brussels-Capital Region , is the capital of Belgium and the de facto capital of the European Union...

     (4° 22' 4.71” E)
  • Antwerp (4° 24' E), used by Mercator, see Meridian of Antwerp
    Meridian of Antwerp
    The Meridian of Antwerp is an analog to the Paris Meridian and Prime Meridian, running through the city of Antwerp, in Flanders, Belgium, and forming the 0° longitude upon which some Belgian maps were based...

  • Bern (7° 26' 22.5” E)
  • Pisa
    Pisa
    Pisa is a city in Tuscany, Central Italy, on the right bank of the mouth of the River Arno on the Tyrrhenian Sea. It is the capital city of the Province of Pisa...

    , Italy
    Italy
    Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...

     (10°24' E)
  • Oslo (Kristiania)
    Oslo
    Oslo is a municipality, as well as the capital and most populous city in Norway. As a municipality , it was established on 1 January 1838. Founded around 1048 by King Harald III of Norway, the city was largely destroyed by fire in 1624. The city was moved under the reign of Denmark–Norway's King...

     (10° 43' 22.5” E)
  • Rome
    Rome
    Rome is the capital of Italy and the country's largest and most populated city and comune, with over 2.7 million residents in . The city is located in the central-western portion of the Italian Peninsula, on the Tiber River within the Lazio region of Italy.Rome's history spans two and a half...

     (12° 27' 08.4” E), meridian of Monte Mario
    Monte Mario
    -External links :* * *...

  • Copenhagen
    Copenhagen
    Copenhagen is the capital and largest city of Denmark, with an urban population of 1,199,224 and a metropolitan population of 1,930,260 . With the completion of the transnational Øresund Bridge in 2000, Copenhagen has become the centre of the increasingly integrating Øresund Region...

     (12° 34' 32.25” E) Rundetårn
    Rundetårn
    The Rundetårn is a 17th-century tower located in central Copenhagen, Denmark. One of the many architectural projects of Christian IV, it was built as an astronomical observatory...

  • Stockholm
    Stockholm
    Stockholm is the capital and the largest city of Sweden and constitutes the most populated urban area in Scandinavia. Stockholm is the most populous city in Sweden, with a population of 851,155 in the municipality , 1.37 million in the urban area , and around 2.1 million in the metropolitan area...

     (18° 3' 29.8” E), at the observatory
    Stockholm Observatory
    The Stockholm Observatory is an astronomical institution in Stockholm, Sweden, founded in the 18th century and today part of Stockholm University...

  • Warsaw
    Warsaw
    Warsaw is the capital and largest city of Poland. It is located on the Vistula River, roughly from the Baltic Sea and from the Carpathian Mountains. Its population in 2010 was estimated at 1,716,855 residents with a greater metropolitan area of 2,631,902 residents, making Warsaw the 10th most...

     (21° 00’ 42” E), see Warsaw meridian
    Warsaw meridian
    The Warsaw meridian is a meridian line running through Warsaw. The local mean time at the meridian was known as Warsaw mean time. It corresponds to an offset from UTC of +01:24....

  • Oradea
    Oradea
    Oradea is the capital city of Bihor County, in the Crișana region of north-western Romania. The city has a population of 204,477, according to the 2009 estimates. The wider Oradea metropolitan area has a total population of 245,832.-Geography:...

    , Romania
    Romania
    Romania is a country located at the crossroads of Central and Southeastern Europe, on the Lower Danube, within and outside the Carpathian arch, bordering on the Black Sea...

     (21° 55' 16” E)
  • Alexandria
    Alexandria
    Alexandria is the second-largest city of Egypt, with a population of 4.1 million, extending about along the coast of the Mediterranean Sea in the north central part of the country; it is also the largest city lying directly on the Mediterranean coast. It is Egypt's largest seaport, serving...

     (29° 53' E)
  • Saint Petersburg
    Saint Petersburg
    Saint Petersburg is a city and a federal subject of Russia located on the Neva River at the head of the Gulf of Finland on the Baltic Sea...

     (30° 19' 42.09” E), Pulkovo meridian
  • Great Pyramid of Giza
    Great Pyramid of Giza
    The Great Pyramid of Giza is the oldest and largest of the three pyramids in the Giza Necropolis bordering what is now El Giza, Egypt. It is the oldest of the Seven Wonders of the Ancient World, and the only one to remain largely intact...

     (31° 8' 3.69” E), 1884
  • Jerusalem (35° 13' 47.1” E), for the small 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 Christians, is a church within the walled Old City of Jerusalem. It is a few steps away from the Muristan....

  • Mecca
    Mecca
    Mecca is a city in the Hijaz and the capital of Makkah province in Saudi Arabia. The city is located inland from Jeddah in a narrow valley at a height of above sea level...

     (39° 49′ 34″ E), see Mecca Time
    Mecca Time
    Mecca Time is a time standard that uses the line of longitude that goes through Mecca, Saudi Arabia as its Prime Meridian. Its proposed use as a global standard is based on the claim that the city is the true center of the Earth and thus should become the basis of the world's timezones...

  • Approximately 59° east of Greenwich
  • Ujjain
    Ujjain
    Ujjain , is an ancient city of Malwa region in central India, on the eastern bank of the Kshipra River , today part of the state of Madhya Pradesh. It is the administrative centre of Ujjain District and Ujjain Division.In ancient times the city was called Ujjayini...

     (75° 47' E), Used from 4th century CE Indian astronomy and calendars.
  • Kyoto
    Kyoto
    is a city in the central part of the island of Honshū, Japan. It has a population close to 1.5 million. Formerly the imperial capital of Japan, it is now the capital of Kyoto Prefecture, as well as a major part of the Osaka-Kobe-Kyoto metropolitan area.-History:...

     (135° 74' E), 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.

The modern Greenwich Meridian, based at the Royal Observatory, Greenwich
Royal Observatory, Greenwich
The Royal Observatory, Greenwich , in London, England played a major role in the history of astronomy and navigation, and is best known as the location of the prime meridian...

, was established by Sir George Airy
George Biddell Airy
Sir George Biddell Airy PRS KCB was an English mathematician and astronomer, Astronomer Royal from 1835 to 1881...

 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 of America is the head of state and head of government of the United States. The president leads the executive branch of the federal government and is the commander-in-chief of the United States Armed Forces....

 Chester A. Arthur
Chester A. Arthur
Chester Alan Arthur was the 21st President of the United States . Becoming President after the assassination of President James A. Garfield, Arthur struggled to overcome suspicions of his beginnings as a politician from the New York City Republican machine, succeeding at that task by embracing...

, 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. On July 16, 1790, the United States Congress approved the creation of a permanent national capital as permitted by the U.S. Constitution....

, USA, for the International Meridian Conference
International Meridian Conference
The International Meridian Conference was a conference held in October 1884 in Washington, D.C., in the United States to determine the Prime Meridian of the world. The conference was held at the request of U.S. President Chester A...

. 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 line 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 Meridian of Antwerp in Antwerp, Belgium....

 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 of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...

 beam emitted northwards 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 reference frame standards, notably through its Earth Orientation Parameter and International Celestial Reference System ...

 (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 space-based global navigation satellite system that provides location and time information in all weather, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites...

 operated by the United States Department of Defense
United States Department of Defense
The United States Department of Defense is the U.S...

. It is the reference meridian in WGS84 and its two 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. This is done in much the same way that a physical standard might be described as a set of procedures for creating a realization of...

 (ITRS) and its realization, the International Terrestrial Reference Frame (ITRF).

The IRM is 5.31 arcseconds east of Airy's transit circle or 102.5 metres (336.3 feet) at the latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...

 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 in Prague, is the change in frequency of a wave for an observer moving relative to the source of the wave. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from...

 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 U.S...

 system. TRANSIT was developed by the Applied Physics Laboratory
Applied Physics Laboratory
The Johns Hopkins University Applied Physics Laboratory , located in Howard County, Maryland near Laurel and Columbia, is a not-for-profit, university-affiliated research center employing 4,500 people. APL is primarily a defense contractor. It serves as a technical resource for the Department of...

 of Johns Hopkins University
Johns Hopkins University
The Johns Hopkins University, commonly referred to as Johns Hopkins, JHU, or simply Hopkins, is a private research university based in Baltimore, Maryland, United States...

. Its lab is located in Howard County, Maryland
Howard County, Maryland
-2010:Whereas according to the 2010 U.S. Census Bureau:*62.2% White*17.5% Black*0.3% Native American*14.4% Asian*0.0% Native Hawaiian or Pacific Islander*3.6% Two or more races*2.0% Other races*5.8% Hispanic or Latino -2000:...

, which was the location of TRANSIT's first ground station. The station's surveyed coordinates in the North American Datum
North American Datum
The North American Datum is the official datum used for the primary geodetic 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 coordinate frame for the Earth, a standard spheroidal reference surface for raw altitude data, and a gravitational equipotential surface that defines the nominal sea level.The latest...

. This shifted the coordinates of any other location on an Earth-centered ellipsoid, especially those far away.

When the antenna of a TRANSIT ground station was mounted directly above Airy's transit circle in June 1969, its longitude on an Earth-centered ellipsoid was 5.64 arcseconds west of TRANSIT's reference meridian. Several small additional longitude shifts were created by 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...

), a dramatic increase in the number of ground stations from only four to over 500, and the use of time-based GPS.

The International Hydrographic Organization
International Hydrographic Organization
The International Hydrographic Organization is the inter-governmental organisation representing the hydrographic community. It enjoys observer status at the UN and is the recognised competent authority on hydrographic surveying and nautical charting...

 adopted an early version of the IRM in 1983 for all nautical charts. The IRM was adopted for air navigation by the International Civil Aviation Organization
International Civil Aviation Organization
The International Civil Aviation Organization , pronounced , , is a specialized agency of the United Nations. It codifies the principles and techniques of international air navigation and fosters the planning and development of international air transport to ensure safe and orderly growth...

 on 3 March 1989. Tectonic plates slowly move over the surface of the 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.

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. Thus this IRM is the weighted average (in the least squares
Least squares
The method of least squares is a standard approach to the approximate solution of overdetermined systems, i.e., sets of equations in which there are more equations than unknowns. "Least squares" means that the overall solution minimizes the sum of the squares of the errors made in solving every...

 sense) of the reference meridians of the hundreds of ground stations contributing to the IERS network. The network includes 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 interferometry 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.Data...

 (VLBI) stations. 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.

Universal Time
Universal Time
Universal Time is a time scale based on the rotation of the Earth. It is a modern continuation of Greenwich Mean Time , i.e., the mean solar time on the Prime Meridian at Greenwich, and GMT is sometimes used loosely as a synonym for UTC...

 is notionally based on the WGS84 meridian. Because of changes in the Earth's rotation, the standard international time UTC
Coordinated Universal Time
Coordinated Universal Time is the primary time standard by which the world regulates clocks and time. It is one of several closely related successors to Greenwich Mean Time. Computer servers, online services and other entities that rely on having a universally accepted time use UTC for that purpose...

 can differ from the mean observed time on the meridian by up to 0.9 second (equivalent to about 260 metres at Greenwich). Leap second
Leap second
A leap second is a positive or negative one-second adjustment to the Coordinated Universal Time time scale that keeps it close to mean 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 , an executive agency and non-ministerial government department of the Government of the United Kingdom, is the national mapping agency for Great Britain, producing maps of Great Britain , and one of the world's largest producers of maps.The name reflects its creation together with...

 (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 Sovereign 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 FRS was an English astronomer and served as Astronomer Royal from 1742, succeeding Edmund Halley. He is best known for two fundamental discoveries in astronomy, the aberration of light , and the nutation of the Earth's axis...

. When Airy's new Prime Meridian ("new" by virtue of Sir George Airy's instrument being placed in a room next to that housing James Bradley's instrument) superseded it fifty years later in 1851, the Ordnance Survey simply continued to use Bradley's.

Other planetary bodies


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:
  • The Prime Meridian of the Moon
    Moon
    The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

     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 lunar 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
    Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...

     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. It is about across and lies within the larger crater Airy in the region Sinus Meridiani....

    .
  • The Prime Meridian of Venus
    Venus
    Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus, the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6, bright enough to cast shadows...

     passes through the central peak in the crater Ariadne.
  • Two different 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 Richard Christopher Carrington
    Richard Christopher Carrington
    Richard Christopher Carrington was an English amateur astronomer whose 1859 astronomical observations demonstrated the existence of solar flares as well as suggesting their electrical influence upon the Earth and its aurorae; and whose 1863 records of sunspot observations revealed the differential...

     started his observations of sunspots. The second is the Stonyhurst heliographic coordinates system.
  • Jupiter
    Jupiter
    Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...

     has several coordinate systems because its cloud tops -- the only part of the planet visible from space -- rotate at different rates depending on latitude. It is unknown whether Jupiter has any internal solid surface that would enable a more Earth-like coordinate system. Scientific Astronomer uses System II coordinates, based on the mean atmospheric rotation of the north and south Equatorial belts. System III coordinates use Jupiter's magnetic field.
  • Titan
    Titan (moon)
    Titan , or Saturn VI, is the largest moon of Saturn, the only natural satellite known to have a dense atmosphere, and the only object other than Earth for which clear evidence of stable bodies of surface liquid has been found....

    , like the Earth's moon, always has the same face towards Saturn, and so that face is 0 longitude.

External links