<P> 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 . The IDL does not extend into Antarctica on the world time zone maps by the United States Central Intelligence Agency (CIA) or the United Kingdom's Her Majesty's Nautical Almanac Office (HMNAO). The IDL on modern CIA maps now reflects the most recent shifts in the IDL (see § Historical alterations below). The current HMNAO map does not draw the IDL in conformity with recent shifts in the IDL; it draws a line virtually identical to that adopted by the UK's Hydrographic Office about 1900 . Instead, HMNAO labels island groups with their time zones, which do reflect the most recent IDL shifts . This approach is consistent with the principle of national and nautical time zones: the islands of eastern Kiribati are actually "islands" of Asian date (west side of IDL) in a sea of American date (east side of IDL). </P> <P> No international organization, nor any treaty between nations, has fixed the IDL drawn by cartographers: the 1884 International Meridian Conference explicitly refused to propose or agree to any time zones, stating that they were outside its purview . The conference resolved that the Universal Day, midnight - to - midnight Greenwich Mean Time (now known as Coordinated Universal Time, or UTC), which it did agree to, "shall not interfere with the use of local or standard time where desirable". From this comes the utility and importance of UTC or "Z (Zulu)" time: it permits a single universal reference for time that is valid for all points on the globe at the same moment . </P> <P> As part of New Spain, the 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 1521 to 1844, the Philippines was one day behind its Asian neighbors (Saturday, 16 March 1521 was the first European visit, when Ferdinand Magellan claimed the area for Spain; colonization began on Friday, 27 April 1565). After Mexico gained its independence from Spain in 1821, Philippine trade interests turned to Imperial China, the 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 1844 from its calendar . The change was also applied to Mariana Islands, Guam and Caroline Islands since they also belonged to Spain . Because of this change, New Year's Eve happened on Monday, 30 December 1844 . Effective Wednesday, 1 January 1845, the Philippines, Guam, Mariana Islands and Caroline Islands switched back to Asian date . Western publications were generally unaware of this change until the early 1890s, so erroneously gave the International Date Line a large western bulge for the next half century . </P> <P> The Russian Empire settled northwest North America from Siberia, from the west with its own Julian calendar (it did not adopt the Gregorian calendar until 1918). The United States purchased Russian America while based in the contiguous United States, from the east with its own Gregorian calendar (adopted in 1752 while several British colonies). The transfer ceremony occurred on the day that the commissioners appointed by the governments of Russia and the United States for that purpose arrived via the USS Ossipee at New Archangel (Sitka), the capital of Russian America . The United States recorded this date as Friday, 18 October 1867 (Gregorian), now known as Alaska Day, whereas the Russian governor, who had remained in New Archangel, would have recorded it as Saturday, 7 October 1867 (Julian). Senator Charles Sumner stated during his three - hour ratification speech (an encyclopedic discussion of Russian America) on Tuesday, 9 April 1867, that this day of the week and calendar discord should be changed . Because the transfer of ownership officially occurred at 3: 30 p.m. Sitka mean solar time (time zones were not yet in use), 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 1867 (Julian) would have been followed by Friday, 18 October 1867 (Gregorian), a duplicate day with a 12 - 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 . </P>

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