The International Date Line (IDL) is an imaginary line on Earth's surface that runs roughly along the 180° longitude line, extending from the North Pole to the South Pole through the Pacific Ocean. It serves as the boundary where one calendar day ends and the next begins
. Crossing the IDL has a unique effect on the calendar date:
- Traveling westward across the line, you add one day.
- Traveling eastward across the line, you subtract one day
The line is not perfectly straight; it zigzags to accommodate political and territorial boundaries, such as bending around eastern Russia, the Aleutian Islands, and some Pacific island groups to keep them on the same calendar day as their respective countries
. The IDL has no formal international legal status and is a convention used to maintain consistent timekeeping worldwide. It is roughly halfway around the world from the Prime Meridian (0° longitude) in Greenwich, England
. In summary, the International Date Line is a practical, imaginary demarcation that helps coordinate global time and date by marking where the date changes by one day when crossed.
