While Greenwich is the global standard, other meridians hold historical or scientific importance.
| Meridian | Longitude | Significance | | :--- | :--- | :--- | | Paris Meridian | 2°20'14.03" E | Rival to Greenwich; used on French maps until 1911. | | Washington Meridian | 77°03'56.05" W | Used by US Navy before 1884. | | Puerto Rico Trench | 66° W | Deepest point in Atlantic, critical for oceanography. | | International Date Line | 180° (approx) | Demarcates calendar days. | meridian longitude
For centuries, sailors could measure latitude easily (using the sun or North Star), but longitude was a deadly puzzle. Ships crashed into coastlines because they didn’t know how far east or west they were. Latitude runs east-west, parallel to the equator
The breakthrough came from John Harrison, an English clockmaker, who invented the marine chronometer—a clock so accurate that sailors could compare ship time with Greenwich time to calculate longitude. It saved countless lives and made global sea travel reliable. Crucially, while latitude has a natural starting point
Most confusion arises between longitude and latitude. Here is the differentiator:
Crucially, while latitude has a natural starting point (the equator at 0°), longitude has no natural zero. You can draw a meridian anywhere. Deciding where "0°" goes was one of the greatest political and scientific debates in history.
Your smartphone doesn’t "look up" longitude; it calculates it using atomic clocks on 31 satellites. Each satellite constantly broadcasts its position and precise time. Your receiver compares the time difference between several satellites to triangulate your longitude and latitude to within centimeters.