Knowra Prime meridian Prime meridian A meridian assigned zero degrees longitude, from which longitude is measured east and west. The chosen prime meridian is a reference convention rather than a uniquely determined line.
Longitude : The angular position of a place east or west of a reference meridian, measured from 0° to 180°. The prime meridian supplies the zero point for measuring it.
Greenwich meridian : The meridian passing through the former Royal Observatory at Greenwich, now used as the international zero-longitude reference. It is the prime meridian adopted by international agreement.
Greenwich Mean Time : Mean solar time historically based on the meridian passing through Greenwich. The Greenwich longitude reference helped connect global timekeeping to a shared meridian.
International Terrestrial Reference Frame : A globally realized reference frame defining Earth-fixed coordinates from geodetic observations. Its zero longitude, the IERS Reference Meridian, differs slightly from the historic Greenwich line.
Meridian (geography) : A half-circle running from one geographic pole to the other, connecting points of equal longitude. The prime meridian is the meridian assigned longitude 0°.
Royal Observatory, Greenwich : A British astronomical observatory founded in 1675 at Greenwich, southeast of central London. Its transit instrument established the historic line chosen as the global reference.
Universal Time : A family of time standards based on Earth’s rotation, including the form known as UT1. Its conventional zero-longitude reference is the modern Greenwich meridian.
IERS Reference Meridian : The internationally adopted zero-longitude reference used in modern geodesy and coordinate systems. It is the precise modern reference, distinct by a small offset from Greenwich’s historic meridian.
Geographic coordinate system : A system for locating positions on Earth using coordinates such as latitude and longitude. Its longitude coordinate depends on a selected zero meridian.
International Meridian Conference : An 1884 meeting in Washington, D.C., that recommended Greenwich as the prime meridian. Delegates selected Greenwich from competing national reference meridians.
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