Time in the United States
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United States time zones are nine standard time zones covering the states and possessions of the United States, used in conjunction with state and national legislation regarding the use of daylight saving time.
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[edit] Daylight Saving Time
As of 2007, DST will begin at 2:00 a.m. on the second Sunday in March (for 2007, this is March 11th) and revert to standard time on the first Sunday in November (for 2007, this is November 4th).
In response to the Uniform Time Act of 1966, each state of the US has officially chosen to apply one of two rules over its entire territory:
- Most use the standard time for their zone (or zones, where a state is divided between two zones), except for using daylight saving time from 2 AM on the first Sunday in April until 2 AM on the last Sunday in October.
- Arizona and Hawaii use standard time throughout the year. However:
- The Navajo Nation observes DST throughout its entire territory, including the portion that lies in Arizona. But the Hopi Nation, which is entirely surrounded by the Navajo Nation, does not observe DST.
- Before 2006, Indiana officially used standard time year-round, with the following exceptions:
- The portions of Indiana that were on Central Time observed Daylight Saving Time.
- Also, some Indiana counties near Cincinnati and Louisville were on Eastern Time, but did (unofficially) observe DST.
- However, in 2005, Indiana passed legislation which took effect on April 2, 2006, that placed the entire state on Daylight Saving Time. See: Time in Indiana
- Daylight Saving Time was extended based on passage of the Energy Policy Act of 2005, Pub. L. No. 109-58, 119 Stat 594 (2005).
[edit] Enumeration of time zones
All time zone abbreviations below are unofficial — only the full names are official.
[edit] Zones used in the contiguous U.S.
From east to west, these zones are:
- Eastern Standard Time (EST; UTC-5; Zone R), which comprises roughly the states on the Atlantic coast and the eastern 2/3rds of the Ohio Valley.
- Central Standard Time (CST; UTC-6; Zone S), which comprises roughly the Gulf Coast, Tennessee Valley, and Great Plains.
- Mountain Standard Time (MST; UTC-7; Zone T), which comprises roughly the states that include the Rocky Mountains.
- Pacific Standard Time (PST; UTC-8; Zone U), which comprises roughly the states on the Pacific coast, plus Nevada.
[edit] Zones used in states beyond the contiguous U.S.
- Alaska Standard Time (AKST; UTC-9; Zone V), which comprises most of the state of Alaska.
- Hawaii-Aleutian Standard Time (or unofficially Hawaii Standard Time) (HST; UTC-10; zone W), which includes Hawaii and most of the length of the Aleutian Islands chain (west of 169°30'W).
[edit] Zones outside the states
- Atlantic Standard Time (AST, UTC-4, Zone Q), which comprises Puerto Rico and the U.S. Virgin Islands.
- Samoa Standard Time (UTC-11, Zone X), which comprises American Samoa.
- Chamorro Standard Time (UTC+10, Zone K), which comprises Guam and the Northern Mariana Islands.
[edit] Boundaries between the zones
(Described from north to south along each boundary.)
[edit] EST/CST boundary
- roughly follows the border between Wisconsin (to west) and the Upper Peninsula of Michigan (to east); the Upper Peninsula counties that border on Wisconsin observe CST, all other counties in the UP observe EST
- follows Lake Michigan
- divides a small portion of northwestern Indiana near Chicago from the rest of the state
- follows the border between Illinois (west) and Indiana (east)
- divides a small portion of southwestern Indiana from the rest of the state
- divides Kentucky roughly in half roughly along a line that is west of Louisville, KY running from northwest to southeast.
- divides the region legally defined as East Tennessee, except for four counties adjoining Middle Tennessee, from the rest of Tennessee.
- follows the border between Alabama (west) and Georgia (east)
- divides most of the western panhandle of Florida just west of Tallahassee, FL from the rest of the state.
[edit] CST/MST boundary
- divides the southwest portion of North Dakota from the rest of the state
- divides South Dakota roughly in half
- divides the western third of Nebraska from the rest of the state
- divides a very small portion of extreme western Kansas (Greeley, Hamilton, Sherman and Wallace counties) from the rest of the state
- follows the border between New Mexico (west) and Oklahoma (east)
- follows the border between New Mexico (west) and Texas (east)
- divides El Paso County and Hudspeth County from the rest of Texas
[edit] MST/PST boundary
- follows the border between northern Idaho (west) and northwestern Montana (east)
- turns west (just south of Nez Perce Pass), following the Salmon River downstream to the Oregon border at the Snake River, dividing the Idaho Panhandle from the rest of the state
- follows the Snake River upstream between Oregon (west) and Idaho (east)
- divides the northern 80% of Malheur County (north of 42°25'N) from the rest of Oregon
- follows the border between Oregon (west) and Idaho (east)
- follows the border (42°N) between Idaho (north) and Nevada (south)
- follows the border between Nevada (west) and Utah (east), except for following city limit line of West Wendover dividing it from the rest of Nevada
- follows the border between Nevada (west) and Arizona (east)
- follows the border between California (west) and Arizona (east)
