nollameridiaani

Nollameridiaani, known in English as the Prime Meridian, is the line of longitude designated as 0°. It serves as the reference point from which all other longitudes are measured, extending from the North Pole to the South Pole. In global geography, it underpins the standard time reference system used worldwide, with Coordinated Universal Time (UTC) tied to conventions of the meridian at Greenwich and its historical counterpart, Greenwich Mean Time (GMT). The zero meridian passes through the Royal Observatory, Greenwich, in London, United Kingdom.

History shows that before the 19th century several nations used different prime meridians for navigation and cartography. In 1884, the International Meridian Conference established Greenwich as the prime meridian for international use, a choice that was subsequently widely adopted on maps and nautical charts. The designation of GMT gradually evolved into UTC as the modern civil time standard, while the geographic zero meridian remains fixed at Greenwich.

Geographic and cartographic role: The nollameridiaani is the central reference line for longitude in most global geodetic systems, including common map projections and navigational charts. Distances east and west of the 0° line are measured in degrees up to 180°. In practice, some regional projections define their own central meridians, but the 0° line remains the universal reference point.

Notes: In Finnish geography and education, nollameridiaani is the standard term for the Prime Meridian. The concept is essential for navigation, astronomy, and timekeeping, and serves as a historical symbol of international cooperation in science and mapping.