Before Greenwich became standard, many countries used their own prime meridians. The (2°20′14″E) was used on French maps for centuries. It is famously referenced in Dan Brown’s novel The Da Vinci Code as the “Rose Line.”
Every measurement needs a starting point. For latitude, nature provides an obvious baseline: the equator. For longitude, however, there is no natural starting point. Any meridian could theoretically serve as the baseline.
Meridians and longitude provide a fundamental framework for locating positions on Earth. Accurate use requires clear datum/reference, awareness of measurement methods and potential errors, and appropriate map projections for practical applications.
Directly opposite the prime meridian lies the at 180° longitude. This line serves as the basis for the International Date Line (IDL) —a zigzagging boundary where the calendar date changes. Crossing the IDL eastward subtracts a day; crossing it westward adds a day. The IDL deviates from the 180° meridian to avoid cutting through countries and island groups, ensuring that political regions remain on the same calendar date. meridian longitude
Today, we no longer need to look at the stars or carry mechanical marine chronometers to find our position. However, the foundational rules of meridian longitude remain critical to modern infrastructure. 1. Global Positioning System (GPS)
Meridian longitude is directly responsible for how we tell time. The Earth rotates 360° on its axis once every 24 hours. By dividing 360 degrees by 24 hours, we find that the Earth rotates .
So the next time you glance at a globe, take a moment to trace a meridian from pole to pole. That simple line connects cultures, enables commerce, and reminds us that we all share the same spinning, spherical Earth—divided only by the coordinates we invented to find our way. Before Greenwich became standard, many countries used their
Meridian Longitude: The Imaginary Lines Shaping Our World Imagine trying to pinpoint your exact location in the middle of the ocean or trying to coordinate a meeting between someone in Tokyo and someone in London. Without a precise, global system of measurement, this would be impossible. Enter —the imaginary lines of longitude that run from the North Pole to the South Pole, serving as the foundation for navigation, cartography, and timekeeping.
This mathematical relationship created the standard time zone system:
Suppose you have a GPS coordinate: 40°44′N, 74°10′W. Here’s what that means in terms of meridian longitude: For latitude, nature provides an obvious baseline: the
如果把地球想象成一个橘子，瓣与瓣之间的分割线就好比子午线。这些线并非随意排列，它们汇聚于两极，为全球定位提供了最基础的网状坐标系统。
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This is the starting point for measuring longitude, designated as 0° longitude. By international agreement, it passes through the Royal Observatory in Greenwich, London.
The reference line for longitude, often called the Prime Meridian, passes through Greenwich, England.