![]() ![]() ![]() Noon occurred at different times but time differences between distant locations were barely noticeable prior to the 19th century because of long travel times and the lack of long-distance instant communications prior to the development of the telegraph. See also: Standard time in the United Statesīefore the adoption of four standard time zones for the continental United States, many towns and cities set their clocks to noon when the sun passed their local meridian, pre-corrected for the equation of time on the date of observation, to form local mean solar time. History Rand McNally Standard Map of the United States, 1921, showing boundaries different from today It is the combination of the time zone and daylight saving rules, along with the timekeeping services, which determines the legal civil time for any U.S. ![]() The clocks run by these services are kept synchronized with each other as well as with those of other international timekeeping organizations. Official and highly precise timekeeping services (clocks) are provided by two federal agencies: the National Institute of Standards and Technology (NIST) (an agency of the Department of Commerce) and the United States Naval Observatory (USNO). The time zone boundaries and DST observance are regulated by the Department of Transportation, but no single map of those existed until the agency announced intentions to make one in September 2022. Indiana introduced DST in 2006.In the United States, time is divided into nine standard time zones covering the states, territories and other US possessions, with most of the country observing daylight saving time (DST) for approximately the spring, summer, and fall months. 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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