These meridians are theoretically the centres of 24 standard time zones in practice, the zones have in many cases been subdivided or altered in shape for the convenience of inhabitants. The present system employs 24 standard meridians of longitude (lines running from the North Pole to the South, at right angles to the Equator) 15º apart, starting with the prime meridian through Greenwich, England. Following this initiative, in 1884 delegates from 27 nations met in Washington, D.C., for the MeridianĬonference and agreed on a system basically the same as that now in use. Sir Sandford Fleming, a Canadian railway planner and engineer, outlined a plan for worldwide standard time in the late 1870s. The need for a standard time was felt most particularly in the United States and Canada, where several extensive railway routes passed through places that differed by several hours in local time. Some such standard became increasingly necessary with the development of rapid railway systems and the consequent confusion of schedules that used scores of different local times kept in separate communities (local time varies continuously with change in longitude). The concept of standard time was adopted in the late 19th century in an attempt to end the confusion that was caused by each community's use of its own solar time. The whole of China, one of the largest countries in the world, has decided to adopt a single time zone. Standard time the time of a town, region or country that is established by law or Indiana introduced DST in 2006.Copyright © 1997 - 2015 Wayana Software. Most of Arizona and Hawaii don't use DST. In addition the uninhabited atolls of Baker Island (AoE) and Wake Island (WAKT) add to the time zone count, making 11 the total number of time zones in the US.Īlmost all states in the US use Daylight Saving Time (DST). There are 9 official time zones according to the law. The time zones in the law are defined by their offset from Coordinated Universal Time (UTC). Code, Title 15, Chapter 6, Subchapter IX - Standard Time. Time zones in the USA are defined in the U.S. Since 1967, the US Department of Transportation (DOT) has been responsible for governing time zones in the country. The US was divided into 4 standard time zones on November 18, 1883, and jurisdiction for the zones was given to the Interstate Commerce Commission (ICC). Time Zones Being Used in Dependencies of United States Offset They will become active again after the next clock change as Daylight Saving Time begins or ends. The above time zones are used during other parts of the year. Time Zones Not Currently Being Observed in United States Offset Note: Local time in these time zones changes when Daylight Saving Time begins and ends. In practice, this means that the local time in these time zones changes when DST begins and ends. For example, Eastern Time (ET) refers to Eastern Standard Time (EST) or Eastern Daylight Time (EDT), depending on which is currently in use. The time zones in the contiguous US are often referred to by their generic name, without making a difference between standard time and Daylight Saving Time designations. Generalized Time Zones in United States Time Zone Abbreviation & Name Since Howland Island and Baker Island constitute the world's westernmost landmasses in relation to the International Date Line, making them the last places on Earth where any date exists, they are sometimes assigned a theoretical 12th time zone called Anywhere on Earth (AoE). As neither Hawaii nor the 5 dependencies use Daylight Saving Time (DST), there are only 6 corresponding DST time zones. In addition, Alaska, Hawaii, and 5 US dependencies all have their own time zones. The contiguous US has 4 standard time zones. However, adding the time zones of 2 uninhabited US territories, Howland Island and Baker Island, brings the total count to 11 time zones. There are 9 time zones by law in the USA and its dependencies. Time Zones Currently Being Used in United States Offset Business Date to Date (exclude holidays).
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