World map with International Date Line

World International Dateline (IDL)Dateline Map and Location Explanation

The IDL is on the opposite side of the Earth to the Prime Meridian. The International Date Line rests roughly on the 180º meridian longitude line in the Central Pacific Ocean, the manmade drawn line that divides two 24 hour calendar days. Over the years, this manmade line has been moved to best suit the needs of the island countries that live next to it(see below) Most of the changes in the shape of this line occur near the Samoan and Kiribati islands. Time zones to the east of the Prime Meridian are in advance of UTC (up to UTC+14); time zones to the west are behind UTC (to UTC-12). The IDL is the line between those highest (up to UTC+14) and those lowest (down to UTC−12) time zones.

The International Date Line and the moving longitude point of midnight separate the two calendar days that are moving and current somewhere on Earth. However, during a two-hour period between 10:00 and 11:59 (UTC) each day, three different calendar days are in use due to the complex IDT shape and rules. This is because of daylight saving in the UTC+12 zone and the use of additional date-shifted time zones in areas roughly east of the 180th meridian. These additional time zones result in the standard time and date in some communities being 24 or 25 hours different from the standard time and date in others.

A World traveler crossing the IDL eastbound removes one day, or 24 hours, so that the calendar date to the west of the line is repeated after the following midnight. Crossing the IDL westbound results in the reverse with 24 hours being added to their watch/calendar, advancing the calendar date by one full day. Having the dateline in the middle ocean was a brilliant idea, since it effects a very small population of people. Can you imagine if the dateline split the United State or some very heavily populated place. Jumping from one day to the next with one foot step would cause massive scheduling and work issues.

Countries and Islands along the dateline

Samoan Islands(Samoa and America Samoa) and Tokelau The IDL passes between Samoa and America Samoa due to a time shift in December 2011. This changed the Samoa side timezone from UTC-11 to UTC-13. This Samoa and Tokelau +13 time change was due to the fact that Samoa wanted to have their hours closer aligned to Australia and New Zealand, since they are close trading partners.

Kwajalein
Kwajalein time is unique and has many special rules it follows. Kwajalein atoll in the Marshall Islands, has been over seen by the United States and used the Hawaiian date, so was placed east of the International Date Line. Kwajalein advanced to the west of the IDL by skipping 21 August 1993 to match the dates used by the rest of the Marshall Islands at the request of its government. As a result of the shift, Kwajalein's work day week was changed to Tuesday - Saturday to match the Hawaiian work week of Monday - Friday on the other side of the IDL (with a remaining difference of two hours due to the two time zones involved, UTC+12 and UTC-10)

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