Line of longitude, at which longitude is defined to be 0°
"Prime Meridian" redirects here. For Earth's prime meridian, often called the Prime Meridian, see IERS Reference Meridian. For the historical meridian it is based on, see Prime meridian (Greenwich).
0°
class=notpageimage|
Modern IERS Reference Meridian on Earth
A prime meridian is an arbitrarily-chosen meridian (a line of longitude) in a geographic coordinate system at which longitude is defined to be 0°. Together, a prime meridian and its anti-meridian (the 180th meridian in a 360°-system) form a great circle. This great circle divides a spheroid, like Earth, into two hemispheres: the Eastern Hemisphere and the Western Hemisphere (for an east-west notational system). For Earth's prime meridian, various conventions have been used or advocated in different regions throughout history.[1] Earth's current international standard prime meridian is the IERS Reference Meridian. It is derived, but differs slightly, from the Greenwich Meridian, the previous standard.[2]
Gerardus Mercator in his Atlas Cosmographicae (1595) used a prime meridian somewhere close to 25°W, passing just to the west of Santa Maria Island in the Azores in the Atlantic Ocean. His 180th meridian runs along the Strait of Anián (Bering Strait)
A prime meridian for a planetary body not tidally locked (or at least not in synchronous rotation) is entirely arbitrary, unlike an equator, which is determined by the axis of rotation. However, for celestial objects that are tidally locked (more specifically, synchronous), their prime meridians are determined by the face always inward of the orbit (a planet facing its star, or a moon facing its planet), just as equators are determined by rotation.
Longitudes for the Earth and Moon are measured from their prime meridian (at 0°) to 180° east and west. For all other Solar System bodies, longitude is measured from 0° (their prime meridian) to 360°. West longitudes are used if the rotation of the body is prograde (or 'direct', like Earth), meaning that its direction of rotation is the same as that of its orbit. East longitudes are used if the rotation is retrograde.[3]
^Norgate & Norgate 2006.
^"What is the Prime Meridian and why is it in Greenwich?". Royal Museums Greeenwich. Archived from the original on 13 December 2021. Retrieved 13 December 2021. The IRM is the only meridian that may now be described as the prime meridian of the world, as it defines 0° longitude by international agreement. The IRM passes 102.5 metres to the east of the historic Prime Meridian of the World at the latitude of the Airy Transit Circle here. The entire Observatory and the historic Prime Meridian now lie to the west of the true prime meridian.
^Archimal, B. A. (2015), Report of the IAU Working Group on Cartographic Coordinates and Rotational Elements: 2015(PDF), p. 27 of 46, archived (PDF) from the original on 6 August 2019, retrieved 6 August 2019, The range of longitudes shall extend from 0° to 360°. Thus, west longitudes are used when the rotation is direct, and east longitudes are used when the rotation is retrograde. ... The Earth, Sun, and Moon do not traditionally follow this definition. Their rotations are direct and longitudes run both east and west 180°, or positive to the east 360°.
0° A primemeridian is an arbitrarily-chosen meridian (a line of longitude) in a geographic coordinate system at which longitude is defined to be 0°. Together...
(secondary coordinates) The 180th meridian or antimeridian is the meridian 180° both east and west of the primemeridian in a geographical coordinate system...
zero degrees longitude (0°N 0°E / 0°N 0°E / 0; 0), i.e., where the primemeridian and the equator intersect. The name is often used in mapping software...
0° The IERS Reference Meridian (IRM), also called the International Reference Meridian, is the primemeridian (0° longitude) maintained by the International...
90th meridian east, located midway between the Primemeridian and the 180th meridian; thus, the center of the Western Hemisphere is on this meridian. In...
no more than a few metres from that imaginary line which is now the primemeridian of the world. — Howse, D. (1997). Greenwich time and the longitude....
International Meridian Conference was a conference held in October 1884 in Washington, D.C., in the United States, to determine a primemeridian for international...
Ante Meridian is a misspelling of: Antimeridian, a meridian at 180° from another or the meridian opposite the primemeridian Ante meridiem, normally abbreviated...
after the meridian. The 90th meridian east forms a great circle with the 90th meridian west. This meridian is halfway between the Primemeridian and the...
long-standing rival to the Greenwich meridian as the primemeridian of the world. The "Paris meridian arc" or "French meridian arc" (French: la Méridienne de...
instrument, Yadav boldly announced his government's ambition to shift the PrimeMeridian from Greenwich, England, to Ujjain, challenging the established international...
lambda (λ). Meridians are imaginary semicircular lines running from pole to pole that connect points with the same longitude. The primemeridian defines 0°...
(primary coordinates) GPX (secondary coordinates) The meridian 100° west of the PrimeMeridian of Greenwich is a line of longitude that extends from the...
The Washington meridians are four meridians that were used as primemeridians in the United States which pass through Washington, D.C. The four that have...
Eastern Hemisphere is the half of the planet Earth which is east of the primemeridian (which crosses Greenwich, London, United Kingdom) and west of the antimeridian...
South Poles. The meridian of the British Royal Observatory in Greenwich, in southeast London, England, is the international primemeridian, although some...
southern halves by the Equator or into western and eastern halves by the Primemeridian. Hemispheres can be divided geographically or culturally, or based on...
to measure in degrees westward from the primemeridian (Greenwich hour angle, GHA), from the local meridian (local hour angle, LHA) or from the first...
Earth. The longitude gives the position east or west of the Moon's primemeridian, which is the line passing from the lunar north pole through the point...
planet Earth that lies west of the PrimeMeridian (which crosses Greenwich, London, England) and east of the 180th meridian. The other half is called the Eastern...
length of the equatorial line across both land and sea. Starting at the PrimeMeridian and heading eastwards, the Equator passes through: The Equator also...
23°26′12.5″N 0°0′0″W / 23.436806°N -0.00000°E / 23.436806; -0.00000 (PrimeMeridian) The Tropic of Cancer, also known as the Northern Tropic, is the Earth's...
about one second of mean solar time at 0° longitude, the currently used primemeridian, and is not adjusted for daylight saving time. The coordination of time...
x), such as longitude (negative values west of PrimeMeridian and positive values east of PrimeMeridian) Vertical coordinate, i.e. height or depth (optional)...
Pole Meridian arc, the distance between two points with the same longitude Primemeridian, origin of longitudes Principal meridian, arbitrary meridians used...
Global Information
