Every has a counterpart on the opposite side of the Earth, exactly 180° away. This is the Antimeridian . While the Prime Meridian divides East from West at 0°, the Antimeridian (180°) serves a very different purpose: it is the rough foundation for the International Date Line (IDL) .

Here’s where it gets practical: . That’s why:

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:

Longitude isn’t just about distance; it’s the foundation of how we measure time. Because the Earth rotates 360° every 24 hours, it moves .

The is the foundational line of the entire longitude system. Designated as 0° longitude, it is the reference from which all other meridians are measured east or west up to 180°.