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International Date Line
An imaginary line on the earth that separates two consecutive calendar days. The date in the Western Hemisphere, to the right of the line, is always one day behind the date in the Eastern Hemisphere. While the line has no force in international law, it is, however, recognized as a convenience.
Without the international date line, travelers headed west would discover on their return that an additional day had passed, even if they kept an accurate record of the number of days traveled. A historic example of this occurred during Magellan's cruise to circumnavigate the globe. Conversely, traveling eastward would result in one day less traveled.
In theory, the international date line can be anywhere on the globe; however, it has been conveniently drawn at 180° from ...