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1.meridian at zero degree longitude from which east and west are reckoned (usually the Greenwich longitude in England)
coordonnée terrestre (fr)[Classe]
coordonnée céleste (fr)[Classe]
carte géographique (fr)[DomainDescrip.]
prime meridian (n.)
||It has been suggested that IERS Reference Meridian be merged into this article or section. (Discuss) Proposed since April 2012.|
A prime meridian is a meridian, i.e. a line of longitude, at which longitude is defined to be 0°. A prime meridian and its opposite in a 360°-system, the 180th meridian (at 180° longitude), form a great circle.
This great circle divides the sphere, e.g. the Earth, into two hemispheres. If one uses directions of East and West from a defined prime meridian, then they can be called Eastern Hemisphere and Western Hemisphere.
An international conference in 1884 decided the prime meridian passes through the Royal Observatory, Greenwich in southeast London, United Kingdom, known simply as the prime meridian but also sometimes referred to as the International Meridian or Greenwich meridian.
As of 2012 the most used[clarification needed] prime meridian for the Earth is the IERS Reference Meridian (IRM). It passes 5.31 arcseconds east of Airy's transit circle or 102.5 metres (336.3 feet) at the latitude of the Royal Observatory, Greenwich, London. A current convention on the earth uses the opposite of the IRM as the basis for the International Date Line.
The modern prime meridian, based at the Royal Observatory, Greenwich, was established by Sir George Airy 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 Chester A. Arthur, 41 delegates from 25 nations met in Washington, D.C., for the International Meridian Conference. 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 for several decades.
The IERS Reference Meridian (IRM), also called the International Reference Meridian, is the reference meridian used as the prime meridian (0° longitude) by the International Earth Rotation and Reference Systems Service (IERS). It passes 5.31 arcseconds east of Airy's transit circle or 102.5 metres (336.3 feet) at the latitude of the Royal Observatory, Greenwich, London. It is also the reference meridian of the Global Positioning System operated by the United States Department of Defense, and of WGS84 and its two formal versions, the ideal International Terrestrial Reference System (ITRS) and its realization, the International Terrestrial Reference Frame (ITRF).
|Country, territory or sea||Notes|
|United Kingdom||The northernmost land on this meridian is near Tunstall in East Riding,Yorkshire.
The southernmost land in the UK is Peacehaven, East Sussex.
|France||The northernmost point on this meridian is in Villers-sur-Mer, Calvados.
The southernmost point is near Gavarnie.
|Spain||Passing just west of Monte Perdido, in the Pyrenees|
|Mediterranean Sea||Gulf of Valencia|
|Mali||This part of Mali has declared independence as Azawad|
|Togo||For about 600 m|
|Ghana||For about 16 km|
|Togo||For about 39 km|
|Ghana||Passing through Lake Volta at|
|Atlantic Ocean||Passing through the Equator at|
|Antarctica||Queen Maud Land, claimed by Norway|
A prime meridian is ultimately arbitrary, unlike an equator, which is determined by the axis of rotation—and various conventions have been used or advocated in different regions and throughout history.
|Locality||GPS longitude||Meridian name||Comment|
|Bering Strait||168°30' W||
|Washington, D.C.||77°00'32.6"W (NAD 83)||Capitol meridian|
|Washington, D.C.||77°02'11.56258"W (NAD 83), 77°02'11.55880"W (NAD 83), 77°02'11.57375"W (NAD 83)||White House Meridian|
|Washington, D.C.||77°2'48.0"W , 77°3'2.3" , 77°3'6.119"W or 77°3'6.276"W (both presumably NAD 27). If NAD27, the latter would be 77°3'5.194"W (NAD 83)||Old Naval Observatory Meridian|
|Washington, D.C.||77°3'56.7"W (1897) or 77°4'2.24"W (NAD 27) or 77°4'1.16"W (NAD 83)||New Naval Observatory Meridian|
|Philadelphia||75° 10' 12” W|
|Rio de Janeiro||43° 10' 19” W|||
|Fortunate Isles / Azores||~ 25° 40′ 32″ W||Used until the middle ages, proposed as one possible neutral meridian by Pierre Janssen at the International Meridian Conference|
|El Hierro (Ferro),
|18° 03' W,
later redefined as
17° 39' 46”? W
|Lisbon||9° 07' 54.862” W|
|Madrid||3° 41' 16.58” W|
|Greenwich||?||United Kingdom Ordnance Survey Zero Meridian|
|-||-||IERS Reference Meridian|
|Paris||2° 20' 14.025” E||Paris meridian|
|Brussels||4° 22' 4.71” E|
|Antwerp||4° 24' E||Antwerp Meridian||used by Mercator|
|Bern||7° 26' 22.5” E|
|Oslo (Kristiania)||10° 43' 22.5” E|
|Florence||11°15' E||Florence Meridian||used in the Peters projection, antipode of a line running through the Bering Strait|
|Rome||12° 27' 08.4” E||meridian of Monte Mario|
|Copenhagen||12° 34' 32.25” E||Rundetårn|
|Naples||14° 15' E|||
|Stockholm||18° 3' 29.8” E||at the Stockholm Observatory|
|Warsaw||21° 00’ 42” E||Warsaw Meridian|
|Oradea||21° 55' 16” E|
|Alexandria||29° 53' E|||
|Saint Petersburg||30° 19' 42.09” E||Pulkovo Meridian|
|Great Pyramid of Giza||31° 8' 3.69” E||1884 |
|Jerusalem||35° 13' 47.1” E||for the small dome of the Church of the Holy Sepulchre|
|Mecca||39° 49′ 34″ E||see Mecca Time Approximately 59° east of Greenwich |
|Ujjain||75° 47' E||Used from 4th century CE Indian astronomy and calendars.|
|Kyoto||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.|
|~ 180||Opposite of Greenwich, proposed 13 Oct 1884 on the International Meridian Conference by Sandford Fleming |
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:
|Wikimedia Commons has media related to: Prime meridian|