Time zone

::Time Zone is also a historical computer game.

History

The first time zone in the world was established by British railways on December 1, 1847—Greenwich Mean Time (GMT) being hand carried on chronometers. About August 23, 1852, time signals were first transmitted by telegraph from the Royal Greenwich Observatory. Even though 98% of the Great Britain's public clocks were using GMT by 1855, it was not made Britain's legal time until August 2, 1880. Some old clocks from this period have two minute hands — one for the local time, one for GMT http://www.wwp-italia.com/info/bristol-time.htm. This only applied to the island of Great Britain, and not to the island of Ireland.

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On November 2, 1868, New Zealand officially adopted a standard time to be observed nationally, and was perhaps the first country to do so. It was based on the longitude 172° 30' East of Greenwich, that is 11 hours 30 minutes ahead of Greenwich Mean Time. This standard was known as New Zealand Mean Time.

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Timekeeping on the American railroads in the mid 19th century was somewhat confused. Each railroad used its own standard time, usually based on the local time of its headquarters or most important terminus, and the railroad's train schedules were published using its own time. Some major railroad junctions served by several different railroads had a separate clock for each railroad, each showing a different time. Pittsburgh main station used six different times! The confusion for travellers making a long journey involving several changes of train can be imagined.

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A system of one-hour standard time zones for American railroads was first proposed by Charles F. Dowd about 1863. He made this proposal while teaching teenage girls, but without publishing anything. He did not even consult railroad officials until 1869. In 1870, he proposed four ideal time zones (having north-south borders), the first centered on Washington, DC, but by 1872 the first was centered 75°W of Greenwich with geographic borders (for example, sections of the Appalachian Mountains). Dowd's system was never accepted by American railroads—instead, U.S. and Canadian railroads implemented their own version on Sunday, November 18, 1883, when each railroad station clock was either advanced or delayed as noon, standard time, was reached within each time zone, east to west. The zones were named Intercolonial, Eastern, Central, Mountain, and Pacific. Within one year, 85% of all cities having populations over 10,000, about 200 cities, were using standard time. A notable exception was Detroit, Michigan, which kept local time until 1900, then vacillated between Central Standard Time, local mean time, and Eastern Standard Time until it settled on EST by ordinance May 1915, ratified by popular vote August 1916. This hodgepodge was made uniform when Standard zone time was made legal by the U.S. Congress in 1918.

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Time zones were first proposed for the entire world by Canada's Sir Sandford Fleming in 1876 as an appendage to the single 24-hour clock he proposed for the entire world (located at the center of the Earth and not linked to any surface meridian!). In 1879 he specified that his universal day would begin at the anti-meridian of Greenwich (now called 180°), while conceding that hourly time zones might have some limited local use. He continued to advocate his system at subsequent international conferences. In October 1884 the International Meridian Conference did not adopt his time zones because they were not within its purview. The conference did adopt a universal day of 24 hours beginning at Greenwich midnight, but specified that it "shall not interfere with the use of local or standard time where desirable." Nevertheless, most major countries had adopted hourly time zones by 1929. Even today, they have not been fully realized, with several time zones keeping a standard time that is not offset by a number of whole hours from Greenwich Mean Time.

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Before 1920, all ships kept local apparent time on the high seas by setting their clocks at night or at the morning sight so that, given the ship's speed and direction, it would be 12 o'clock when the Sun crossed the ship's meridian (12 o'clock = local apparent noon). During 1917, at the Anglo-French Conference on Time-keeping at Sea, it was recommended that all ships, both military and civilian, should adopt hourly standard time zones on the high seas. Whenever a ship was within the territorial waters of any nation it would use that nation's standard time. The captain was permitted to change his ship's clocks at a time of his choice following his ship's entry into another time zone—he often chose midnight. These zones were adopted by all major fleets between 1920 and 1925 but not by many independent merchant ships until World War II. On February 9, 1942, the United States switched from Eastern Standard Time to Eastern War Time (Eastern Daylight Time maintained year round) and switched back to Eastern Standard Time on September 30, 1945.

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Time on a ship's clocks and in a ship's log had to be stated along with a "zone description", which was the number of hours that was to be added to zone time to obtain GMT, hence zero in the Greenwich time zone, and negative numbers from −1 to −12 for time zones to the east and positive numbers from +1 to +12 to the west (hours, minutes, and seconds for nations without an hourly offset). These signs are opposite to those given below because ships must obtain GMT from zone time, not zone time from GMT. All zones were pole-to-pole staves 15° wide except for −12 and +12, which were each 7.5° wide separated by a longitude of 180°. Unlike the zig-zagging land-based International Date Line, the nautical International Date Line follows 180° except where it is interrupted by territorial waters and the lands they border, including islands. About 1950, a letter suffix was added to the zone description, assigning Z to the zero zone, and A-M (except J) to the east and N-Y to the west (J may be assigned to local time in non-nautical applications). These were to be vocalized using a phonetic alphabet which included Zulu for GMT, leading sometimes to the use of the term 'Zulu Time'.

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These nautical letters have been added to some time zone maps, like the map of Standard Time Zones by Her Majesty's Nautical Almanac Office (NAO), which extended the letters by adding an asterisk (*) or dagger (†) for areas that do not use a nautical time zone, and a double dagger (‡) for areas that do not have a legal standard time (Greenland's ice sheet and all of Antarctica—The United Kingdom specifies UTC − 3 for the Antarctic Peninsula, but no other country recognizes that). They conveniently ignore any zone that does not have an hour or half-hour offset, so a double dagger (‡) has been co-opted for these zones below.

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In maritime usage, GMT retains its historical meaning of UT1, the mean solar time at Greenwich. UTC, atomic time at Greenwich, is too inaccurate, differing by as much as 0.9 s from UT1, creating an error of 0.4 km in longitude at the equator. However, DUT can be added to UTC to correct it to within 50 ms of UT1, reducing the error to only 20 m.

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