Date-line

The date-line is an imaginary line on the surface of the Earth which skirts the 180 roughly {{E}} meridian (is and western) in the Pacific Ocean and whose role is to indicate the place where it is necessary to change date when it is crossed.

Goal

Each day at midnight, in all the time zones, it is necessary to change date to pass to the next day. But taking into account the use of a Meridian of reference for these time zones, there exists also a meridian line where, whatever the hour, it is necessary when one crosses it to add or cut off one day, according to the direction of the crossing.

Thus, somebody travelling towards the West and crossing the date-line must add one day to the date which it would expect to have if it did not do it. Similarly, a traveller towards the East must cut off one day. At the precise moment where it is midnight on the date-line, all the planet is at the same date.

The date-line can appear diverting, particularly on short air ways which lead to cross it. For example, a traveller on the basis of the Tonga (islands located in the time zone UTC+13) to go to the Samoa (UTC-11) by plane carries out a two hours way between two places where the standard time differs from 24 heures ; consequently, if it leaves Tonga at midday Tuesday, it will arrive at the Samoa at 2 o'clock in the afternoon Monday. Another example was the flight charter of Air Kiribati (policy-holder by Aloha Airlines) at the beginning of Hawaii: party Sunday morning at 6 a.m., the Boeing 737 arrived on the Christmas island three hours after… Monday, then after having made stopover, turned over to Honolulu Sunday in the afternoon.

History

By considering the round Earth, the need for a date-line had been predicted by Arab and French theorists as of the Middle Ages. But the first manifestation of the phenomenon appeared at the time of the Circumnavigation of Magellan: the crew, of return in Spain, was persuaded of the day of the week, was attested by various logbooks perfectly maintained up to date. In same time, the people with ground ensured that the day was different. The problem - although perfectly comprehensible as of this time as Antonio Pigafetta showed it, sailor and chronicler embarked in forwarding - caused debates, until sending a special delegation near the pope for explaining to him.

This situation, seemingly paradoxical, was used as arises dramatic in several novels, of which the Round the world tour in eighty days of Jules Verne and the Island of the day of before of Umberto Eco.

Localization

The date-line follows for its greater part the meridian line of 180° of longitude. But in two places, the line was deviated in order to prevent that countries, particularly archipelagoes of the Pacific, are with horse on two dates (a situation more difficult to manage than the fact of being on several time zones).

In the Northern Pacific Ocean, the line first of all deviates towards the East through the Bering Strait then towards the Western along the Aleutian Islands in order to maintain all the Russia and all the Alaska on both sides.

In the Pacific Ocean central, the date-line was moved in 1995 in order to circumvent the Kiribati rather than to pass through. Before this modification, the Kiribati were constantly with horse over two days and the administrations on both sides of the line could be contacted only four working days per week. Another consequence was that the island Caroline, the atoll more in the east of the country, was the first ground to enter the year 2000, a situation that the Kiribati, like the Neighboring states, sought to exploit at tourist ends.

See too

Internal bonds

Meridian Time zone
universal Time coordinated

External bonds

has History off the International Dates Line

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