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The evolution of United States standard time zone boundaries from 1919 to 2024 in five-year increments. Plaque in Chicago marking the creation of the four time zones of the continental US in 1883 Colorized 1913 time zone map of the United States, showing boundaries very different from today Map of U.S. time zones during between April 2, 2006, and March 11, 2007.
Four standard time zones for the continental United States were introduced at noon on November 18, 1883, in Chicago, IL, when the telegraph lines transmitted time signals to all major cities. [ 4 ] [ 5 ]
Chief meteorologist at the United States Weather Bureau Cleveland Abbe divided the United States into four standard time zones for consistency among the weather stations. In 1879, he published a paper titled Report on Standard Time. [13] In 1883, he convinced North American railroad companies to adopt his time-zone system.
A standardised time system was first used by British railways on 1 December 1847, when they switched from local mean time, which varied from place to place, to Greenwich Mean Time (GMT). It was also given the name railway time , reflecting the important role the railway companies played in bringing it about.
In the United States, the problems were much more severe, with one table showing over 100 local times varying by more than 3 hours. In 1870, Charles F. Dowd published a pamphlet titled A System of national time and its application advocating three time zones across the country based on the Washington meridian , modifying this to four zones ...
The instant that was designated as "December 31.5 GMT" in 1924 almanacs became "January 1.0 GMT" in 1925 almanacs. The term Greenwich Mean Astronomical Time ( GMAT ) was introduced to unambiguously refer to the previous noon-based astronomical convention for GMT. [ 17 ]
North of the Salmon River, that is between the Oregon state border and the Idaho County/Lemhi County border; west of the Idaho County/Lemhi County border, that is between the Salmon River and the Montana state border: UTC−08:00 PST Pacific Standard Time Illinois: UTC−06:00 CT: Yes: Central Indiana: UTC−05:00 ET Yes
Such designations can be ambiguous; for example, "CST" can mean China Standard Time (UTC+08:00), Cuba Standard Time (UTC−05:00), and (North American) Central Standard Time (UTC−06:00), and it is also a widely used variant of ACST (Australian Central Standard Time, UTC+9:30). Such designations predate both ISO 8601 and the internet era; in ...