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. Each time zone is generally about 15 degrees wide, about one hour ahead or behind its neighboring. The ITU recognizes a total of 40 time zones, which are generally centered around these 24 primary meridians. Since 1967, the US Department of Transportation (DOT) has been responsible for governing time zones in the country. The ITU defines time zones based on the world’s 24 primary meridians, each 15 degrees apart and running north-south around the Earth. 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 That year, the United States was divided into four time zones roughly centered on the 75th, 90th, 105th, and 120th meridians. Until 1883 most railway companies relied on some 100 different, but consistent, time zones. 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). The problem of keeping track of over 300 local times was overcome by establishing railroad time zones. 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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