|
The International Date Line (IDL) is an imaginary line of navigation on the surface of the Earth that runs from the north pole to the south pole and demarcates the change of one calendar day to the next. It passes through the middle of the Pacific Ocean, roughly following the 180° line of longitude but deviating to pass around some territories and island groups. ==Geography== For parts of its length, the IDL follows the meridian of 180° longitude, roughly down the middle of the Pacific Ocean. To avoid crossing nations internally, the IDL deviates west around the US Aleutian Islands, separating them from islands in the far east of Russia, and further south, it deviates east around various island nations in the Pacific such as Kiribati, Samoa, Tonga and Tokelau. These various deviations, east or west, generally accommodate the political and/or economic affiliations of the affected areas. Proceeding from north to south, the first deviation of the IDL from 180° is to pass to the east of Wrangel Island and the Chukchi Peninsula, the easternmost part of Russian Siberia. It then passes through the Bering Strait between the Diomede Islands at a distance of 1.5 km (1 mi) from each island. It then bends considerably west of 180°, passing west of St. Lawrence Island and St. Matthew Island and finally bisecting the Aleutian Islands between those belonging to the US -- Attu Island being the westernmost—and the Commander Islands belonging to Russia. It then bends southeast again to return to 180°. Thus all of Russia is to the west of the IDL and all of the USA to the east. Two uninhabited atolls, Howland Island and Baker Island, just north of the equator in the central Pacific Ocean (and ships at sea between 172.5°W and 180°) have the latest time on Earth of UTC-12 hours. The IDL circumscribes Kiribati by swinging far to the east, almost reaching the 150° meridian. Kiribati's easternmost islands, the southern Line Islands south of Hawaii, have the most advanced time on Earth, UTC+14 hours. South of Kiribati, it returns westwards but remains east of 180°, passing between Samoa and American Samoa;〔http://www.samoadatechange.com/the-sdc-story/〕 accordingly, Samoa, Tokelau, Wallis and Futuna, Fiji, Tonga, Tuvalu and New Zealand's Kermadec Islands and Chatham Islands have the same date, while American Samoa, the Cook Islands, Niue, and French Polynesia are one day behind. (The IDL then bends southwest to return to 180°.) A person who goes around the world from east to west (the same direction as Magellan's voyage) would lose one hour for every 15° of longitude crossed, and would lose 24 hours for one circuit of the globe from east to west if they did not compensate by adding 24 hours when they crossed the IDL. In contrast, a west-to-east circumnavigation of the globe gains an hour for every 15° of longitude crossed and requires subtracting 24 hours when crossing the IDL. The IDL must therefore be observed in conjunction with the Earth's time zones: on crossing it in either direction, the calendar ''date'' is adjusted by one day. For the two hours between 10:00 and 11:59 (UTC) each day, in summer three different days are observed at the same time in different places. For example, at UTC time Thursday 10:15, it is Wednesday 23:15 in American Samoa, (UTC-11), and Friday 00:15 in Kiritimati (UTC+14). For the first hour (UTC 10:00–10:59), this is true for both inhabited and uninhabited territories, but during the second hour (UTC 11:00–11:59) it is only true in an uninhabited maritime time zone twelve hours behind UTC (UTC-12). According to the clock, the first areas to experience a new day and a New Year are islands that use UTC+14, the Line Islands, and in the southern summer also Samoa. The first major city is Auckland, New Zealand. The areas that are the first to see the daylight of a new day vary by the season. On , it is a large part of the Chukchi Peninsula, which uses UTC+12 and experiences midnight sun on this date. At New Year, the first places to see daylight are the South Pole and McMurdo Station in Antarctica, which both experience midnight sun. Both use UTC+13 as daylight saving time. At equinox, the first place to see daylight is the uninhabited Caroline Island, which is the easternmost land located west of the IDL, and among inhabited places it is Kiritimati. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「International Date Line」の詳細全文を読む スポンサード リンク
|