Geographic coordinate that specifies the east-west position of a point on the Earth's surface
For other uses, see Longitude (disambiguation).
A graticule on the Earth as a sphere or an ellipsoid. The lines from pole to pole are lines of constant longitude, or meridians. The circles parallel to the Equator are circles of constant latitude, or parallels. The graticule shows the latitude and longitude of points on the surface. In this example, meridians are spaced at 6° intervals and parallels at 4° intervals.
Map of Earth
Longitude (λ)
Lines of longitude appear vertical with varying curvature in this projection, but are actually halves of great ellipses, with identical radii at a given latitude.
Latitude (φ)
Lines of latitude appear horizontal with varying curvature in this projection; but are actually circular with different radii. All locations with a given latitude are collectively referred to as a circle of latitude.
The equator divides the planet into a Northern Hemisphere and a Southern Hemisphere, and has a latitude of 0°.
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Geodesy
Fundamentals
Geodesy
Geodynamics
Geomatics
History
Concepts
Geographical distance
Geoid
Figure of the Earth (radius and circumference)
Geodetic coordinates
Geodetic datum
Geodesic
Horizontal position representation
Latitude / Longitude
Map projection
Reference ellipsoid
Satellite geodesy
Spatial reference system
Spatial relations
Vertical positions
Technologies
Global Nav. Sat. Systems (GNSSs)
Global Pos. System (GPS)
GLONASS (Russia)
BeiDou (BDS) (China)
Galileo (Europe)
NAVIC (India)
Quasi-Zenith Sat. Sys. (QZSS) (Japan)
Discrete Global Grid and Geocoding
Standards (history)
NGVD 29
Sea Level Datum 1929
OSGB36
Ordnance Survey Great Britain 1936
SK-42
Systema Koordinat 1942 goda
ED50
European Datum 1950
SAD69
South American Datum 1969
GRS 80
Geodetic Reference System 1980
ISO 6709
Geographic point coord. 1983
NAD 83
North American Datum 1983
WGS 84
World Geodetic System 1984
NAVD 88
N. American Vertical Datum 1988
ETRS89
European Terrestrial Ref. Sys. 1989
GCJ-02
Chinese obfuscated datum 2002
Geo URI
Internet link to a point 2010
International Terrestrial Reference System
Spatial Reference System Identifier (SRID)
Universal Transverse Mercator (UTM)
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Longitude (/ˈlɒndʒɪtjuːd/, AU and UK also/ˈlɒŋɡɪ-/)[1][2] is a geographic coordinate that specifies the east–west position of a point on the surface of the Earth, or another celestial body. It is an angular measurement, usually expressed in degrees and denoted by the Greek letter lambda (λ). Meridians are imaginary semicircular lines running from pole to pole that connect points with the same longitude. The prime meridian defines 0° longitude; by convention the International Reference Meridian for the Earth passes near the Royal Observatory in Greenwich, south-east London on the island of Great Britain. Positive longitudes are east of the prime meridian, and negative ones are west.
Because of the Earth's rotation, there is a close connection between longitude and time measurement. Scientifically precise local time varies with longitude: a difference of 15° longitude corresponds to a one-hour difference in local time, due to the differing position in relation to the Sun. Comparing local time to an absolute measure of time allows longitude to be determined. Depending on the era, the absolute time might be obtained from a celestial event visible from both locations, such as a lunar eclipse, or from a time signal transmitted by telegraph or radio. The principle is straightforward, but in practice finding a reliable method of determining longitude took centuries and required the effort of some of the greatest scientific minds.
A location's north–south position along a meridian is given by its latitude, which is approximately the angle between the equatorial plane and the normal from the ground at that location.
Longitude is generally given using the geodetic normal or the gravity direction. The astronomical longitude can differ slightly from the ordinary longitude because of vertical deflection, small variations in Earth's gravitational field (see astronomical latitude).
^"Definition of LONGITUDE". Merriam-Webster. Archived from the original on 16 June 2018. Retrieved 14 March 2018.
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