WHAT IS THE INTERNATIONAL DATE LINE?
This imaginary line separates time, running from the North Pole to the South Pole
WORDS TOM GARLINGHOUSE
The international date line (IDL) is an imaginary line that runs along Earth’s surface from the North Pole to the South Pole in the middle of the Pacific Ocean. When you cross it, you either gain or lose a day depending on which way you are travelling. If you’re travelling westward you gain a day, and if you’re travelling eastward you lose a day. For example, if a traveller moves eastward across the Pacific Ocean from Wake Island to the Hawaiian Islands on 2 December, they will jump backwards to 1 December as soon as they cross the IDL. If they were travelling in the opposite direction, they would arrive at Wake Island on 3 December. Although the traveller seems to move back or forward in time, there’s no physics-defying magic going on here. The international date line is based on a rational, practical system of universal timekeeping that takes into account the movement of Earth around the Sun.