What Is 0 Longitude

Content on WhatAnswers is provided "as is" for informational purposes. While we strive for accuracy, we make no guarantees. Content is AI-assisted and should not be used as professional advice.

Last updated: April 11, 2026

Quick Answer: Zero longitude, also known as the Prime Meridian, is the reference line passing through Greenwich, London, established at the International Meridian Conference in 1884. It serves as the baseline for measuring longitude globally, dividing Earth into the Eastern and Western hemispheres at 0° coordinates.

Key Facts

Established officially on October 13, 1884, at the International Meridian Conference attended by 26 nations
Located at the Royal Observatory in Greenwich, London, England, marked by a brass line on the ground
Divides Earth into the Eastern Hemisphere (0° to 180°E) and Western Hemisphere (0° to 180°W)
Combined with latitude coordinates, enables precise identification of any location on Earth using geographic coordinates
Forms the basis of Greenwich Mean Time (GMT), now known as Coordinated Universal Time (UTC)

Overview

Zero longitude, commonly referred to as the Prime Meridian, is an imaginary line running from the North Pole to the South Pole that passes through Greenwich, London, England. Established as the international standard reference meridian in 1884, it represents the 0° point from which all other longitudes on Earth are measured, both east and west.

The Prime Meridian holds profound significance in global navigation, cartography, and timekeeping. Before its official adoption, numerous countries maintained their own reference meridians, creating confusion in maritime navigation and international commerce. The establishment of a universal standard revolutionized global coordination and remains fundamental to modern geography, GPS technology, and international time standards used worldwide.

How It Works

Zero longitude functions as the foundational reference line for measuring geographic position:

Baseline Reference: All longitudes are measured in degrees east (+) or west (−) from the Prime Meridian, with measurements ranging from 0° to 180° in each direction
Coordinate System: Combined with latitude measurements, zero longitude creates a grid system enabling the identification of any point on Earth using precise geographic coordinates (latitude, longitude)
Hemisphere Division: The Prime Meridian serves as the dividing line between the Eastern Hemisphere and Western Hemisphere, creating clear geographic reference zones for navigation and mapping
Navigation Standard: Maritime and aviation navigation systems rely on this reference point to determine course headings, distances, and accurate position fixes using instruments like sextants and GPS receivers

Key Comparisons

Aspect	Prime Meridian (0°)	International Date Line (180°)	Other Reference Meridians
Purpose	Reference point for longitude measurement	Divides calendar days globally	Historical local references (discontinued)
Location	Greenwich, London, England	Primarily Pacific Ocean near 180° longitude	Paris (2°E), Washington DC, others (no longer official)
Adoption Date	Officially October 1884	Recognized alongside Prime Meridian in 1884	Varied; replaced by Prime Meridian standard
Global Recognition	Universally accepted international standard	Accepted with regional variations	Obsolete for international navigation

Why It Matters

Global Navigation: Modern GPS systems, maritime navigation, and aviation routing depend entirely on the Prime Meridian as the fundamental reference for longitude calculations and course plotting
Timekeeping Standard: The Prime Meridian established Greenwich Mean Time (GMT), which evolved into Coordinated Universal Time (UTC), the international standard for civil timekeeping, telecommunications, and scientific research
Cartographic Accuracy: Maps, atlases, and geographic information systems (GIS) use the Prime Meridian to ensure consistent spatial representation of Earth's surface across all nations and institutions
International Coordination: From financial markets to telecommunications networks, global infrastructure relies on the standardized geographic and temporal reference system established by the Prime Meridian

The Prime Meridian represents more than a simple geographic line; it embodies humanity's commitment to standardization and international cooperation. Its selection of Greenwich, influenced by Britain's dominant maritime power in 1884, has proven remarkably durable. Today, despite technological advances that could support alternative standards, the Prime Meridian remains universally accepted, demonstrating the power of established conventions in global systems. This reference line continues enabling seamless international communication, navigation, and coordination across all human activities.