International Date Line [IDL]

Updated: 2017-03-27.

The International Date Line, or IDL, is an arbitrary line going from north to south that marks where one calendar day ends and another begins. Unlike the Prime Meridian, which is located on the opposite side of the earth, it does not go straight north to south, but rather goes around several island groups for logistical reasons.

Traveling east over the International Date Line will cause one to go back one day, to the previous calendar day by about a full 24 hours. Traveling west across the International Date Line causes one to move up about a full calendar day.

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