They are not parallel to each other. They are farthest apart at the equator.
): The opposite side of the world, where the date changes [NOAA]. The Prime Meridian: A History of Convention The Prime Meridian ( 0∘0 raised to the composed with power
The challenge for centuries was not defining the lines, but agreeing on a starting point. Unlike the Equator, which is a physical inevitability defined by the Earth's rotation, there is no "natural" starting line for longitude. It is entirely arbitrary. For much of history, different nations used different capital cities as "zero degrees," creating chaos in international navigation.
The time at the Prime Meridian (0°) serves as the global baseline.
: Longitude is measured in degrees, minutes, and seconds. Values range from 0° to 180° East, and 0° to 180° West. Historical Significance and the Greenwich Standard meridian longitude
: The Prime Meridian and the International Date Line together divide the Earth into the Eastern Hemisphere and the Western Hemisphere.
In geography, a is an imaginary half-circle that runs from the North Pole to the South Pole. Unlike lines of latitude (which are parallel circles that never touch), all meridians are the same length and intersect at the poles.
But 18th-century clocks broke on the rolling, humid, salt-sprayed decks of ships. Consequently, ships missed islands, crashed into reefs, or got lost for months. The British Parliament passed the , offering a prize of £20,000 (millions in today's money) for a practical solution.
To understand longitude, one must first visualize the Earth’s geometry. While lines of latitude run parallel to the equator, growing progressively smaller as they approach the poles, lines of longitude, known as meridians, behave differently. A meridian is a great circle that runs from the North Pole to the South Pole. Unlike latitude, where the equator serves as a natural zero point, the Earth has no natural starting point for measuring east-west travel. Consequently, every meridian is the same length, and they intersect the equator at right angles. Longitude is the angular distance, measured in degrees, east or west of a primary reference line known as the Prime Meridian. They are not parallel to each other
Why Greenwich? In the 19th century, Britain was the dominant naval and industrial power. British cartographers had already produced the most accurate nautical charts, and most of the world's shipping used Greenwich as their reference. At the International Meridian Conference in Washington, D.C., 22 nations voted to make Greenwich the world's Prime Meridian. France abstained (preferring Paris) but eventually adopted the standard.
Because the Earth rotates 360 degrees every 24 hours, it moves exactly . Therefore, longitude is directly tied to time. To know your longitude at sea, you needed to know two things simultaneously:
Conversely, if your local noon occurs after GMT, you are West.
Unlike latitude parallels (which run parallel to the Equator), meridians are great circles —they are all the same length, and each one crosses the Equator at a right angle. Every meridian longitude line converges at the poles. If you stand at the geographic North Pole, every direction is technically south, and every meridian passes directly under your feet. The Prime Meridian: A History of Convention The
The meridian longitude system is more than just lines on a map; it is a universal language of space and time. It bridges the gap between ancient celestial navigation and modern satellite technology, ensuring that no matter where we are on the globe, we can always find our way home.
Over 70% of the world's shipping commerce at the time already used charts based on the Greenwich meridian. How Meridians Form Global Time Zones
Directly opposite the Prime Meridian (0°) is the 180° meridian. This line, located mostly in the Pacific Ocean, acts as the . When you cross this line moving west, you gain a day; moving east, you lose a day. 3. Spatial Reference (GIS)