# Relationship between prime meridian and international date line

### A History of the International Date Line - International Meridian Conference

The International Date Line is an imaginary boundary that runs from east to line east or west of this is measured in terms of its proximity to the Prime Meridian. the time difference between countries on either side of the line is not exactly What is the Prime Meridian and where is the International Date Line? Longitude is an imaginary line that runs from the North Pole to the South Pole and is Longitude can be calculated by knowing the time difference at a given location and. Before discussing how and why the International Date Line came to be, we should In , England designated the Prime Meridian (0 degrees That difference will depend on how far east or west one is located within a.

## International Date Line

This is to keep countries in that area from being divided into separate time zones, such as Polynesia. Although it would seem that way from the description, the time difference between countries on either side of the line is not exactly 24 hours.

It depends on local time zone factors and varies depending on where in the world the divide is located. To explain why it exists in simpler terms, let's say you're going to travel around the world and the International Date Line doesn't exist. When you move into a new time zone you must either subtract an hour if you're going east or add an hour if you're going west.

Therefore, by the time you pass through all of the time zones, you'll have jumped ahead - or fallen back - a day from the actual calendar date. Things would get pretty messed up if we didn't account for this shift.

The International Date Line prevents the date from being uncoordinated with the real calendar. If you cross the IDL during travel while you're moving in an easterly direction, you must subtract a day, but if you cross the date line moving in the opposite direction - west - then you must add a day.

Ultimately, it helps keep everyone across the world synced up with the real time. Night and day is illustrative only; daylight hours depend on latitude and time of year. Description[ edit ] This description is based on the most common understanding of the de facto International Date Line. In other places, however, the IDL deviates east or west away from that meridian. Lawrence Island and St. The IDL crosses between the U. Two US-owned uninhabited atolls, Howland Island and Baker Islandjust north of the equator in the central Pacific Ocean and ships at sea between It follows that meridian until reaching Antarcticawhich has multiple time zones.

Conventionally, the IDL is not drawn into Antarctica on most maps.

The IDL must therefore be observed in conjunction with the Earth's time zones: Facts dependent on the IDL[ edit ] For the two hours between For example, at During the first hour UTC During the second hour UTC These include portions of the Republic of Kiribatiincluding Millennium Island in the Line Islandsas well as Samoa during the southern summer.

As a result, this atoll was renamed Millennium Island.

Understanding Time Zones

At the equinoxesthe first place to see daylight would be the uninhabited Millennium Island in Kiribati, which is the easternmost land located west of the IDL. All nations unilaterally determine their standard time zonesapplicable only on land and adjacent territorial waters. This date line can be called de facto since it is not based on international law, but on national laws.

These national zones do not extend into international waters. The nautical date linenot the same as the IDL, is a de jure construction determined by international agreement.

### What Is the International Date Line for?

It is the result of the Anglo-French Conference on Time-keeping at Seawhich recommended that all ships, both military and civilian, adopt hourly standard time zones on the high seas.

The United States adopted its recommendation for U. This date line is implied but not explicitly drawn on time zone maps. In reality, ships use these time zones only for radio communication and similar purposes. For internal purposes, such as work and meal hours, ships use a time zone of their own choosing. Cartographic practice and convention[ edit ] The IDL on the map on this page and all other maps is based on the de facto line and is an artificial construct of cartographers, as the precise course of the line in international waters is arbitrary.

Similarly, the western Aleutian Islands are islands of American date in a sea of Asian date.

• What Is the International Date Line for?
• international date line

No international organization, nor any treaty between nations, has fixed the IDL drawn by cartographers: The conference resolved that the Universal Day, midnight-to-midnight Greenwich Mean Time now known as Coordinated Universal Time, or UTCwhich it did agree to, "shall not interfere with the use of local or standard time where desirable".

The Philippine Islands are shown pre, while Alaska is shown post Philippines and [ edit ] As part of New Spainthe Philippines long had its most important communication with Acapulco in Mexico and was accordingly on the east side of the IDL despite being at the far western edge of the Pacific Ocean.

From tothe Philippines was one day behind its Asian neighbors Saturday, 16 March was the first European visit, when Ferdinand Magellan claimed the area for Spain; colonization began on Friday, 27 April After Mexico gained its independence from Spain inPhilippine trade interests turned to Imperial Chinathe Dutch East Indies and adjacent areas, so the Philippines decided to shift back to the west side of the IDL by removing Tuesday, 31 December from its calendar.

Western publications were generally unaware of this change until the early s, so erroneously gave the International Date Line a large western bulge for the next half century. The United States purchased Russian America while based in the contiguous United Statesfrom the east with its own Gregorian calendar adopted in while several British colonies. Senator Charles Sumner stated during his three-hour ratification speech an encyclopedic discussion of Russian America on Tuesday, 9 Aprilthat this day of the week and calendar discord should be changed.

Sitka mean solar time time zones were not yet in use[13] that was the date and time that Alaska changed from an Asian and Julian date to an American and Gregorian date.

If the transfer had occurred at the preceding midnight then Friday, 6 October Julian would have been followed by Friday, 18 October Gregoriana duplicate day with a day difference appropriate both for changing from an Asian date to an American date equivalent to moving the IDL from the east to the west of Alaska and for changing from the Julian calendar to the Gregorian calendar during the 19th century.

### What is the difference between the prime meridian and the international date line

In that year, King Malietoa Laupepa was persuaded by American traders to adopt the American date three hours behind California to replace the former Asian date four hours ahead of Japan. Being 21 hours behind made business difficult because having weekends on backward days meant only four days of the week were shared workdays.

Tokelau is a territory of New Zealand north of Samoa whose principal transportation and communications links with the rest of the world pass through Samoa. During that period it was west of the IDL.

Because of that, Kwajalein used the Hawaiian date, so was effectively east of the International Date Line unlike the rest of the Marshalls. Kwajalein returned to the west side of the IDL by removing Saturday, 21 August from its calendar to match the dates used by the rest of the Marshall Islands, at the request of its government.

Along with the shift, Kwajalein's work week was changed to Tuesday through Saturday to match the Hawaiian work week of Monday through Friday on the other side of the IDL. As a result, the country straddled the IDL. Government and commercial concerns on opposite sides of the line could only conduct routine business by radio or telephone on the four days of the week which were weekdays on both sides. To eliminate this anomaly, Kiribati introduced a change of date for its eastern half by removing Saturday, 31 December from its calendar.