Crossing the International Date Line is one of the rare thrills of travel. Pass over the Pacific Ocean in the right direction (eastward) and you can relive the same day twice. We left Guam on Thursday and arrived in Hawaii on Wednesday, the night before.

The date line actually used to be in Europe. About 150 years ago, days were measured from noon to noon, starting and ending at the Prime Meridian. When an international conference of leaders changed it to midnight, the date line moved to the middle of the Pacific.

The result creates some fascinating time realities. Even though they’re just 40 miles apart, American Samoa and the independent state of Samoa are constantly separated on the calendar. With two