The International Date Line .

The International Date Line, established in 1884, passes through the mid-Pacific Ocean and roughly follows a 180 degrees longitude north-south line on the Earth. It is located halfway round the world from the prime meridian—the zero degrees longitude established in Greenwich, England, in 1852.

International Date Line, also called Date Line, imaginary line extending between the North Pole and the South Pole and arbitrarily demarcating each calendar day from the next. It corresponds along most of its length to the 180th meridian of longitude but deviates eastward through the Bering Strait to avoid dividing Siberia and then deviates westward to include the Aleutian Islands with Alaska. South of the Equator, another eastward deviation allows certain island groups to have the same day as New Zealand.



The International Date Line is a consequence of the worldwide use of timekeeping systems arranged so that local noon corresponds approximately to the time at which the sun crosses the local meridian of longitude (see Standard Time). A traveler going completely around the world while carrying a clock that he advanced or set back by one hour whenever he entered a new time zone and a calendar that he advanced by one day whenever his clock indicated midnight would find on returning to his starting point that the date according to his own experience was different by one day from that kept by persons who had remained at the starting point. The International Date Line provides a standard means of making the needed readjustment: travelers moving eastward across the line set their calendars back one day, and those traveling westward set theirs a day ahead.

Circumnavigating the globe

People traveling westward around the world must set their clocks:


Back by one hour for every 15° of longitude crossed, and

Forward by 24 hours upon crossing the International Date Line.

For anyone traveling eastward, they must set their clocks:



Forward by one hour for every 15° of longitude crossed, and

Back by 24 hours upon crossing the International Date Line.

Failing to do this would make their time inaccurate to the local time.



The Arab geographer Abulfeda (1273–1331) predicted that circumnavigators would accumulate a one-day offset to the local date.[1] This phenomenon was confirmed in 1522 at the end of the Magellan–Elcano circumnavigation (1519–1522), the first successful circumnavigation. After sailing westward around the world from Spain, the expedition called at Cape Verde for provisions on Wednesday, 9 July 1522 (ship's time). However, the locals told them that it was actually Thursday, 10 July 1522. The crew was surprised, as they had recorded each day of the three-year journey without omission.[2] Cardinal Gasparo Contarini, the Venetian ambassador to Spain, was the first European to give a correct explanation of the discrepancy

Ushakovskoye, Russia ( 77*56'N 178*29'W )


Diomede Island, Alaska, USA ( 65*45'N 168*57'W )


Attu, Aleution Islands, USA ( 52*53'N 173*04'E )


Nikolskoye, Bering Is, Russia ( 55*12'N 165*59'E )


Tarawa, Kiribati ( 1*28'N 173*02'E )



Pago Pago, American Samoa ( 14*16'S 170*42'W )


Apia, Samoa ( 13*50'S 171*45'W )


Chatham Islands, NZ ( 44*02'S 176*26'W )


McMurdo Station, Antarctica ( 77*50'S 166*40'W )