Time Zones
As the earth rotates on its axis from west to east, night and day arrive at different parts of the earth at different times. Until the late 1800s, every town, county, or isolated group of islands observed its own time and set clocks according to the local sunrise and sunset. Time differences between locations were practically unnoticeable, however, because it took days, weeks, or months to travel, and instant modes of communication did not exist.
Demand for a unified time system evolved as a result of two technological advances: the telegraph and the locomotive. In the 1830s, the telegraph made possible instantaneous communication between distant points, and the first locomotives developed in England and America made rapid travel possible. With the development of telegraph and railroad networks on a continental scale in North America, Europe, and elsewhere, local times came into conflict for it was nearly impossible to create schedules or to relay messages effectively. Railroads wrote timetables and set station clocks accordingly; yet, these schedules were not coordinated among the railroad companies or among political areas.
American meteorologist Cleveland Abbe, who helped found the United States Weather Bureau in 1870, pioneered a system of weather reporting and forecasting using the telegraph to collect and disseminate information. As accurate timekeeping was important to accurate weather forecasting, Abbe persuaded North American railroads to adopt time zones by 1883.
The following year an international system of 24 time zones was adopted. The line of 0° longitude, which runs through the Greenwich Observatory at London, England, is the prime, or starting, meridian. The zones extending east from Greenwich increase one hour each for a total of 12 hours. The zones extending west decrease by a total of 12 hours. The 24th zone is divided by the International Date Line (IDL), at 180° longitude. The time difference on either side of the line is 24 hours, one day greater west of the line than east of it.
Major deviations from the ideal zone system exist. For instance, Newfoundland and the Cook Islands are located in half-hour zones. In the former Soviet Union, all time zones are one hour greater than the zones adopted in 1884. Time zone boundaries, especially in populated areas, are deliberately defined along political boundaries or physical features. Even the IDL, which runs down the center of the pacific Ocean, has been flexed through the Bering Strait so that Siberia and Alaska are entirely within their own time units.
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