Like many aspects of geography, the International Date Line isn’t so much a physical boundary as it is a human construct that tries to make sense of the world we live in. It sits roughly on the 180-degree line of longitude in the middle of the Pacific Ocean, and its purpose is to separate calendar days based on the Greenwich Meridian half a planet away. Everything to the left of the Date Line is one day ahead of everything to the right; it also separates the Eastern and Western hemispheres. Things get interesting when you get to Polynesia, where Tonga and American Samoa are in the same time zone but are one day apart, because American Samoa is in the Western Hemisphere on the far side of the International Date Line from Tonga. If you travel farther west, you’ll find that the time in Fiji is one hour earlier than Tonga. These exceptions have been made over the years by independent nations to improve commerce and convenience for their trading partners. Crossing the International Date Line is a unique experience, as it’s the only place in the world where you can either add or lose an entire day in a single second!