Universal Time

Universal Time (UT) is a timescale based on the rotation of the Earth. It is a modern continuation of the Greenwich Mean Time (GMT), i.e., the mean solar time on the meridian of Greenwich, England, which is the conventional 0-meridian for geographic longitude. GMT is sometimes used, incorrectly, as a synonym for UTC. The old GMT has been split, in effect into UTC and UT1.

Universal Time and standard time

Prior to the introduction of standard time, every municipality set its clock, if it had one, by the local position of the sun. This served well until the introduction of the train, when it became possible to travel fast enough to require almost constant re-setting of clocks. Standard time, where all clocks in a region use the same time, was invented to solve this problem.

Related Topics:
Train - Clock

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Standard time divides the world into a number "time zones", each one covering, in theory at least, 15 degrees. All clocks within each of these zones would be set to the same time as the others, but so as to differ by one hour from those in the neighbouring zones. The local time at the Royal Greenwich Observatory in Greenwich, England was chosen as standard at the 1884 International Meridian Conference, leading to the widespread use of Greenwich Mean Time in order to set local clocks. This location was chosen because by 1884 two-thirds of all charts and maps already used it as their prime meridian. The conference rejected Sir Sandford Fleming's time zones because they were outside the purpose for which it was called, to choose a prime meridian. Nevertheless, by 1929 all major countries had adopted time zones.

Related Topics:
Time zone - Royal Greenwich Observatory - Prime meridian - Sandford Fleming - 1929

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In the United States and Canada, standard time zones were introduced on November 18, 1883, by American and Canadian railroads. Newspapers referred to that day as "the Day of Two Noons." There was no legislative enactment or ruling: the railroads simply adopted a five zone system and assumed the public would follow. The American Railway Association, an organization of railroad managers, had noticed growing scientific interest in standardizing time. The ARA devised their own system, which had irregular zone boundaries which followed then-existing boundaries of different lines, partly in order to head off government action which might have been inconvenient to their operations. Most people simply accepted the new time, but a number of cities and counties refused to accept "railroad time", which, after all, had not been made law. In, for example, the expiration of a contract--what does "midnight" mean? In one Iowa Supreme Court case, the owner of a saloon argued that he operated by local (sun) time, not "railroad time," and so he had not violated laws about closing time. Standard time remained a local matter until 1918, when it was made law as part of the introduction of daylight saving.

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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.

Related Topics:
New Zealand - Standard time

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