Every meridian is a "Great Circle" arc. While there are an infinite number of possible meridians, the world operates on a 360-degree system. The starting point, known as the , passes through the Royal Observatory in Greenwich, England. From this line, coordinates are measured up to 180° East and 180° West.
To understand meridian coordinates, one must first understand the geometry of the Earth. A meridian is not a full circle, but a semi-circle—an imaginary arc running from the geographic North Pole to the geographic South Pole. Unlike lines of latitude, which are parallel and never meet, every meridian intersects at the poles. This specific geometry dictates how they function as coordinates. meridian coordinates
: In the UTM (Universal Transverse Mercator) system, the Earth is divided into 60 zones, each with its own "central meridian" to keep map distortions to a minimum. 📍 Fast Fact: The "Moving" Meridian Every meridian is a "Great Circle" arc
This alignment is why early star catalogs are essentially a map of Earth’s coordinate system projected onto the heavens. By knowing the precise meridian coordinates of a star, a navigator could determine their ship’s longitude at sea. From this line, coordinates are measured up to
: Paired with latitude, they pinpoint any exact location on Earth.
The term "meridian" comes from the Latin meridies , meaning "midday," because the sun passes through a given meridian at solar noon. Why They Matter
Meridian coordinates are expressed in degrees of longitude, ranging from 0° at the Prime Meridian to 180° east or west. The 180th meridian, roughly corresponding to the International Date Line in the Pacific Ocean, is where the coordinate system "wraps around." It is here that one day turns into the next.