Prime meridian
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A prime meridian is a meridian in a geographic coordinate system at which longitude is defined to be 0°. On a spheroid, a prime meridian and its anti-meridian form a great ellipse. This divides the bo
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)
The line of the Greenwich meridian at the Royal Observatory, Greenwich, England
The prime meridian sign in Parnay, Maine-et-Loire, France
Prime meridian sign near Somanya, Ghana
180th meridian
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The 180th meridian or antimeridian is the meridian 180° both east and west of the prime meridian in a geographical coordinate system. The longitude at this line can be given as either east or west. On
180° Meridian, Taveuni, Fiji. The man pictured is facing southward.
Marine sandglass MMM