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definitions - Prime_Meridian

prime meridian (n.)

1.meridian at zero degree longitude from which east and west are reckoned (usually the Greenwich longitude in England)

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prime meridian (n.)


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Prime meridian

                   
Zero meridian and longitude 0° redirect here.
Line across the Earth
Prime Meridian

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,[1] known simply as the prime meridian[2] but also sometimes referred to as the International Meridian or Greenwich meridian[citation needed].

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.[3][4][5] A current convention on the earth uses the opposite of the IRM as the basis for the International Date Line.

Contents

  Prime meridian at Greenwich

  Markings of the prime meridian at the Royal Observatory, Greenwich.
  Gerardus Mercator in his Atlas Cosmographicae (1595) uses a prime meridian in the Atlantic, intended to separate the Old World (Eurasia and Africa) and the New World (the Americas) into two hemispheres. Mercator's 180th meridian runs along the Strait of Anián (Bering strait), while his prime meridian corresponds to somewhere close to 25° W, passing just to the west of Santa Maria Island.

The modern prime meridian, based at the Royal Observatory, Greenwich, was established by Sir George Airy in 1851.[6] 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.[1] However, France abstained from the vote and French maps continued to use the Paris meridian for several decades.

  IERS Reference Meridian

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.[3][4][5] 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).

  From Pole to Pole

Starting at the North Pole and heading south to the South Pole, the prime meridian and IERS Reference Meridian pass through:

Co-ordinates
(approximate)
Country, territory or sea Notes
90°0′N 0°0′E / 90°N 0°E / 90; 0 (North Pole) Arctic Ocean
81°39′N 0°0′E / 81.65°N 0°E / 81.65; 0 (Greenland Sea) Greenland Sea
72°53′N 0°0′E / 72.883°N 0°E / 72.883; 0 (Norwegian Sea) Norwegian Sea
61°0′N 0°0′E / 61°N 0°E / 61; 0 (North Sea) North Sea
53°45′N 0°0′E / 53.75°N 0°E / 53.75; 0 (United Kingdom)  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.
50°47′N 0°0′E / 50.783°N 0°E / 50.783; 0 (English Channel) English Channel
49°19′N 0°0′E / 49.317°N 0°E / 49.317; 0 (France)  France The northernmost point on this meridian is in Villers-sur-Mer, Calvados.
The southernmost point is near Gavarnie.
42°41′N 0°0′E / 42.683°N 0°E / 42.683; 0 (Spain)  Spain Passing just west of Monte Perdido, in the Pyrenees
39°56′N 0°0′E / 39.933°N 0°E / 39.933; 0 (Mediterranean Sea) Mediterranean Sea Gulf of Valencia
38°52′N 0°0′E / 38.867°N 0°E / 38.867; 0 (Spain)  Spain
38°38′N 0°0′E / 38.633°N 0°E / 38.633; 0 (Mediterranean Sea) Mediterranean Sea
35°50′N 0°0′E / 35.833°N 0°E / 35.833; 0 (Algeria)  Algeria
21°50′N 0°0′E / 21.833°N 0°E / 21.833; 0 (Mali)  Mali This part of Mali has declared independence as  Azawad
14°59′N 0°0′E / 14.983°N 0°E / 14.983; 0 (Burkina Faso)  Burkina Faso
11°6′N 0°0′E / 11.1°N 0°E / 11.1; 0 (Togo)  Togo For about 600 m
11°6′N 0°0′E / 11.1°N 0°E / 11.1; 0 (Ghana)  Ghana For about 16 km
10°57′N 0°0′E / 10.95°N 0°E / 10.95; 0 (Togo)  Togo For about 39 km
10°36′N 0°0′E / 10.6°N 0°E / 10.6; 0 (Ghana)  Ghana Passing through Lake Volta at 7°48′N 0°0′E / 7.8°N 0°E / 7.8; 0 (Lake Volta)
5°37′N 0°0′E / 5.617°N 0°E / 5.617; 0 (Atlantic Ocean) Atlantic Ocean Passing through the Equator at 0°0′N 0°0′E / 0°N 0°E / 0; 0 (Equator)
60°0′S 0°0′E / 60°S 0°E / -60; 0 (Southern Ocean) Southern Ocean
68°54′S 0°0′E / 68.9°S 0°E / -68.9; 0 (Antarctica) Antarctica Queen Maud Land, claimed by  Norway

  History

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
  • Behring Strait offered 1884 as possibility for a "neutral prime meridian" by Pierre Janssen at the International Meridian Conference [7]
  • Range 168º15' and 168°45' suggested by Urion Argador [8]. The opposite which is 11°30' E is close to the Florence Meridian of 11°15' E that is used in the Peters World Map.
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 [9]
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[10]
El Hierro (Ferro),
Canary Islands
18° 03' W,
later redefined as
17° 39' 46”? W
Ferro Meridian [11]
Lisbon 9° 07' 54.862” W
Madrid 3° 41' 16.58” W
Greenwich  ? Greenwich meridian?
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
Pisa 10°24' 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 [12]
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 [13]
Saint Petersburg 30° 19' 42.09” E Pulkovo Meridian
Great Pyramid of Giza 31° 8' 3.69” E 1884 [14]
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 [15]
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 [16]

  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 lies directly in the middle of the face of the moon visible from Earth and passes near the crater Bruce.
  • The prime meridian of Mars is defined by the crater Airy-0.
  • The prime meridian of Venus passes through the central peak in the crater Ariadne.[17]
  • 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 started his observations of sunspots.[18] The second is the Stonyhurst heliographic coordinates system.
  • Jupiter has several coordinate systems because its cloud tops -- the only part of the planet visible from space -- rotate at different rates depending on latitude.[19] 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, like the Earth's moon, always has the same face towards Saturn, and so that face is 0 longitude.

  References

  1. ^ a b International prime meridian was chosen by the International Meridian Conference, Washington DC, October 1884. McCarthy, P. Kenneth; Seidelmann (2009). TIME from Earth Rotation to Atomic Physics. Weinheim: Wiley-VCH. pp. 244–5. 
  2. ^ ROG Learing Team (23 August 2002). "The Prime Meridian at Greenwich". Royal Museums Greenwich. Royal Museums Greenwich. http://www.rmg.co.uk/explore/astronomy-and-time/astronomy-facts/history/the-prime-meridian-at-greenwich. Retrieved 14 June 2012. 
  3. ^ a b History of the Prime Meridian -Past and Present
  4. ^ a b IRM on grounds of Royal Observatory from Google Earth Accessed 30 March 2012
  5. ^ a b The astronomic latitude of the Royal Observatory is 51°28'38"N whereas its latitude on the European Terrestrial Reference Frame (1989) datum is 51°28'40.1247"N.
  6. ^ Greenwich Observatory ... the story of Britain's oldest scientific institution, the Royal Observatory at Greenwich and Herstmonceux, 1675-1975 p.10. Taylor & Francis, 1975
  7. ^ International Conference Held at Washington for the Purpose of Fixing a Prime Meridian and a Universal Day. October, 1884. Project Gutenberg
  8. ^ http://www.reissmann.info/bibliotheke/projektoi/AUXhA%20--%2019372-07-06%20=%202006-03-25%20--%20Argadorian%20Calendar%20--%20en.pdf
  9. ^ Atlas do Brazil, 1909, by Barão Homem de Mello e Francisco Homem de Mello, published in Rio de Janeiro by F. Briguiet & Cia.
  10. ^ http://www.gutenberg.org/files/17759/17759-h/17759-h.htm
  11. ^ Ancient, used in Ptolemy's Geographia. Later redefined 17° 39' 46” W of Greenwich to be exactly 20° W of Paris. French "submarin" at Washington 1884.
  12. ^ http://www.gutenberg.org/files/17759/17759-h/17759-h.htm
  13. ^ The meridian of Ptolemy's Almagest.
  14. ^ Wilcomb E. Washburn, "The Canary Islands and the Question of the Prime Meridian: The Search for Precision in the Measurement of the Earth"
  15. ^ Maimonides, Hilchot Kiddush Hachodesh 11:17, calls this point אמצע היישוב, "the middle of the habitation", i.e. the habitable hemisphere. Evidently this was a convention accepted by Arab geographers of his day.
  16. ^ http://www.gutenberg.org/files/17759/17759-h/17759-h.htm
  17. ^ "USGS Astrogeology: Rotation and pole position for the Sun and planets (IAU WGCCRE)". http://astrogeology.usgs.gov/Projects/WGCCRE/constants/iau2000_table1.html. Retrieved 22 October 2009. 
  18. ^ "Carrington heliographic coordinates". http://www.encyclopedia.com/doc/1O80-Carringtonheligrphccrdnts.html. 
  19. ^ "Planetographic Coordinates". http://documents.wolfram.com/applications/astronomer/AdditionalInformation/PlanetographicCoordinates.html. Retrieved 2009-06-19. 

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