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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.
Null Island is the location at zero degrees latitude and zero degrees longitude), i.e., where the prime meridian and the equator intersect. Since there is no landmass located at these coordinates, it is not an actual island. The name is often used in mapping software as a placeholder to help find and correct database entries that have ...
The most important reason for the 5.3 seconds of longitude offset between the IERS Reference Meridian and the Airy transit circle is that the observations with the transit circle were based on the local vertical, while the IERS Reference is a geodetic longitude, that is, the plane of the meridian contains the center of mass of the Earth.
The astronomical longitude of the Greenwich prime meridian was found to be 0.19″ ± 0.47″ E, i.e. the plane defined by the local vertical on the Greenwich prime meridian and the plane passing through Earth's rotation axis on the ITRF zero meridian are effectively parallel.
Longitude is given as an angular measurement with 0° at the Prime Meridian, ranging from −180° westward to +180° eastward. The Greek letter λ (lambda) [38] [39] is used to denote the location of a place on Earth east or west of the Prime Meridian. Each degree of longitude is sub-divided into 60 minutes, each of which is divided into 60 ...
Longitude measures the rotational angle between the zero meridian and the measured point. By convention for the Earth, Moon and Sun, it is expressed in degrees ranging from −180° to +180°. For other bodies a range of 0° to 360° is used. For this purpose, it is necessary to identify a zero meridian, which for Earth is usually the Prime ...
The WGS 84 meridian of zero longitude is the IERS Reference Meridian, [8] 5.3 arc seconds or 102 metres (335 ft) east of the Greenwich meridian at the latitude of the Royal Observatory. [ 9 ] [ 10 ] (This is related to the fact that the local gravity field at Greenwich does not point exactly through the Earth's center of mass, but rather ...
In other words, it is a coordinate line for longitudes, a line of longitude. The position of a point along the meridian at a given longitude is given by its latitude , measured in angular degrees north or south of the Equator .