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Worldwide time zones at present. Standard time is the synchronization of clocks within a geographical region to a single time standard, rather than a local mean time standard. Generally, standard time agrees with the local mean time at some meridian that passes through the region, often near the centre of the region.
The history of standard time in the United States began November 18, 1883, when United States and Canadian railroads instituted standard time in time zones. Before then, time of day was a local matter, and most cities and towns used some form of local solar time , maintained by some well-known clock (for example, on a church steeple or in a ...
Time zones of the world. A time zone is an area which observes a uniform standard time for legal, commercial and social purposes. Time zones tend to follow the boundaries between countries and their subdivisions instead of strictly following longitude, because it is convenient for areas in frequent communication to keep the same time.
It is ultimately the authority of the secretary of transportation, in coordination with the states, to determine which regions will observe which of the standard time zones and if they will observe daylight saving time. [7] As of August 9, 2007, the standard time zones are defined in terms of hourly offsets from UTC. [8]
Standard time zones of the world. The number at the bottom of each zone specifies the number of hours to add to UTC to convert it to the local time. As international commerce increased, the need for an international standard of time measurement emerged. Several authors proposed a "universal" or "cosmic" time (see Time zone § Worldwide time zones).
The Uniform Time Act of 1966, Pub. L. 89–387, 80 Stat. 107, enacted April 13, 1966, was a Law of the United States to "promote the adoption and observance of uniform time within the standard time zones" prescribed by the Standard Time Act of 1918.
The Standard Time Act of 1918, also known as the Calder Act, was the first United States federal law implementing Standard time and Daylight saving time in the United States. [2] It defined five time zones for the continental United States and authorized the Interstate Commerce Commission to define the limits of each time zone.
He proposed 24 time zones, each an hour wide or 15 degrees of longitude. The zones were labelled A-Y, excluding J, and arbitrarily linked to the Greenwich meridian, which was designated G. All clocks within each zone would be set to the same time as the others, and between zones the alphabetic labels could be used as common notation.