Meridian — Longitude

is a geographic coordinate that specifies the east‑west position of a point on Earth’s surface. It is measured as an angle from the prime meridian (0° longitude) to the meridian passing through the point, ranging from 0° to 180° east or west.

In the age of digital mapping, meridian longitude is more relevant than ever. Global Positioning System (GPS) coordinates use decimal degrees of longitude and latitude to provide accuracy down to a few centimeters. meridian longitude

The history of is one of life, death, and genius. For centuries, sailors could measure latitude easily (using the North Star or the sun at noon). But longitude was a murderous puzzle. is a geographic coordinate that specifies the east‑west

meridian generally marks the International Date Line in the Pacific Ocean. 3. The Prime Meridian and the Universal Day But longitude was a murderous puzzle

The most famous meridian, the Prime Meridian, serves a dual role in geography and timekeeping. It serves as the reference point for Coordinated Universal Time (UTC). When it is noon at the Prime Meridian, it is effectively the start of the day for that time zone, and every other time zone on Earth is calculated as an offset (plus or minus hours) from this line. Additionally, the meridian opposite the Prime Meridian, located at roughly 180 degrees, serves as the basis for the International Date Line. Crossing this invisible line alters the calendar day, a fascinating mathematical necessity to keep the global calendar synchronized with Earth's rotation.

In the age of sail, determining longitude was the greatest scientific challenge of the era, requiring the invention of highly accurate clocks (chronometers). Today, while we have to do the heavy lifting, the concept of meridian longitude remains essential for: