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World Geography25 Essential Exam Concepts
The Prime Meridian GK Facts, Greenwich History & Study Guide
The Prime Meridian is the internationally designated north-south reference line defined as zero degrees (0°) longitude, from which all geographic longitudes east and west are measured across the globe. Together with the antipodal 180th meridian, it divides the planet into the Eastern and Western Hemispheres. While the Equator is naturally fixed by the physical rotation of the Earth as the midpoint between the geographic poles, longitudinal meridians possess no inherent physical baseline. Historically, individual maritime empires established arbitrary national prime meridians through their capital cities, such as Paris, Cadiz, and Ferro, creating widespread navigational confusion and dangerous railway scheduling errors during the nineteenth-century expansion of global transit.
The international standardization of the Greenwich Meridian was formally established at the International Meridian Conference convened in Washington, D.C., in October 1884. Organized by United States President Chester A. Arthur and attended by delegates representing twenty-five sovereign nations, the conference selected the meridian passing through the Airy Transit Circle telescope at the Royal Observatory in Greenwich, London. The selection reflected practical maritime realities: by 1884, more than seventy-two percent of global commercial shipping tonnage already relied on navigational charts published by the British Admiralty based on the Greenwich meridian. Twenty-two nations voted in favor of the resolution, establishing an enduring universal standard for international cartography and astronomical reckoning.
Geographically, the Prime Meridian traverses eight sovereign nations across Europe and Africa: the United Kingdom, France, Spain, Algeria, Mali, Burkina Faso, Togo, and Ghana, before crossing the Southern Ocean into Antarctica. It provides the mathematical datum for Greenwich Mean Time and its modern atomic successor, Coordinated Universal Time, dividing the planet into twenty-four hourly time zones spaced fifteen degrees apart. In contemporary satellite geodesy, the physical Airy meridian has been refined by the International Earth Rotation and Reference Systems Service Reference Meridian, which lies approximately 102.5 metres east of the historical brass line at Greenwich to maintain exact alignment with the GPS World Geodetic System 1984 ellipsoid.
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The Prime Meridian is the arbitrarily designated geographical line of 0° longitude, functioning as the universal origin for measuring global east-west distance.
Unlike the Equator, which is a naturally fixed physical parallel defined by Earth's rotational axis, the Prime Meridian is an internationally agreed human convention.
The Greenwich Meridian was selected as the international prime meridian at the International Meridian Conference held in Washington, D.C., in October 1884.
The conference was attended by delegates from 25 nations, with 22 voting in favor of Greenwich, one voting against (Dominican Republic), and two abstaining (France and Brazil).
Greenwich was selected because over 72% of the world's merchant shipping fleet was already using nautical charts calculated from the Greenwich Observatory.
The exact physical location was anchored to the crosshairs of the Airy Transit Circle, an astronomical instrument designed by British Astronomer Royal Sir George Biddell Airy in 1851.
The Prime Meridian passes through eight sovereign countries: the United Kingdom, France, Spain, Algeria, Mali, Burkina Faso, Togo, and Ghana.
The meridian also traverses the Antarctic continent across Queen Maud Land, where national territorial claims converge toward the South Pole.
The combination of the Prime Meridian (0°) and the Antimeridian (180°) bisects the Earth into the Eastern Hemisphere and Western Hemisphere.
The Antimeridian at 180° longitude forms the general basis for the International Date Line (IDL), which zigzags through the Pacific Ocean to avoid splitting island nations.
Because the Earth completes a 360° rotation in 24 hours, each 15° of longitude corresponds to exactly one hour of solar time difference.
Localities situated east of Greenwich are ahead in time (+UTC), while localities situated west of Greenwich are behind in time (-UTC).
The Royal Observatory at Greenwich, London, was originally founded in 1675 by King Charles II to improve maritime navigation and determine longitude at sea.
The British Parliament passed the Longitude Act in 1714, which offered a massive financial reward won by clockmaker John Harrison for inventing the marine chronometer.
France continued to use the Paris Meridian for cartography until 1911 and for timekeeping until 1914 before formally adopting Greenwich standard time.
In modern satellite navigation, the IERS Reference Meridian (IRM) maintained by the International Earth Rotation and Reference Systems Service replaces the historical visual marker.
The modern GPS zero meridian (WGS 84) lies approximately 102.5 metres (5.3 arcseconds) east of the historical brass line at the Greenwich Observatory.
India’s Standard Meridian is 82°30' E, passing through Mirzapur near Prayagraj in Uttar Pradesh, establishing Indian Standard Time (IST) at exactly UTC+05:30.
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