Time in the United States 579351 226058907 2008-07-16T17:20:29Z 198.45.18.70 /* CST/MST boundary */ double hyphen to em-dash '''Time in the United States''', by law, is divided into nine standard [[time zone]]s covering the states and its possessions, with most of the [[United States]] observing [[daylight saving time]] for part of the year. The time zone boundaries and DST observance are under the authority of the [[United States Department of Transportation|Department of Transportation]]. Official and highly precise time keeping services (clocks) are provided by two federal time agencies: a Department of Commerce agency, the [[National Institute of Standards and Technology]] (NIST), and its military counterpart, the [[United States Naval Observatory]] (USNO). The clocks run by these services are kept highly synchronized with each other as well as with those of international time keeping organizations. It is the combination of the time zone and daylight saving rules along with the time keeping services which determines the legal [[civil time]] for any U.S. location at any moment. [[Image:TimeZonesUSA large.png|right|thumb|330px|Map of U.S. time zones between [[April 2]], [[2006]], and [[March 11]], [[2007]]. The current situation is different only in that [[Pulaski County, Indiana]] is now in the Eastern time zone and no longer in the Central time zone.]] == United States time zones == Standard time zones in the United States are currently defined at the federal level by law ''[[Title 15 of the United States Code|15 U.S.C.]] [http://www.law.cornell.edu/uscode/15/260.html §260]''. The federal law also establishes the transition dates and times at which [[daylight saving time]] occurs, if observed. It is ultimately the authority of the [[United States Secretary of Transportation|Secretary of Transportation]], in coordination with the states, to determine which regions will observe which of the standard time zones and if they will observe daylight saving time. As of [[August 9]], [[2007]], the standard time zones are defined in terms of hourly offsets from [[Coordinated Universal Time|UTC]].<ref>[http://thomas.loc.gov/cgi-bin/bdquery/z?d110:h2272: H.R.2272 — America COMPETES Act] (Sec. 3013)</ref> Prior to this they were based upon the [[mean solar time]] at several meridians 15° apart west of [[Royal Observatory, Greenwich|Greenwich]] ([[GMT]]). Only the full time zone names listed below are official; abbreviations are by common use conventions. === Zones used in the contiguous U.S. === From east to west, these zones are: * [[Eastern Time Zone (North America)|Eastern standard time zone]]: (EST; [[UTC-5]]; Zone R), which comprises roughly the states on the [[Atlantic coast]] and the eastern two thirds of the [[Ohio Valley]]. * [[Central Time Zone (North America)|Central standard time zone]]: (CST; [[UTC-6]]; Zone S), which comprises roughly the [[Gulf Coast]], [[Tennessee Valley]], and [[Great Plains]]. * [[Mountain Standard Time Zone|Mountain standard time zone]]: (MST; [[UTC-7]]; Zone T), which comprises roughly the states that include the [[Rocky Mountains]]. * [[Pacific Standard Time Zone|Pacific standard time zone]]: (PST; [[UTC-8]]; Zone U), which comprises roughly the states on the [[Pacific coast]], plus [[Nevada]]. === Zones used in states beyond the contiguous U.S. === * [[Alaska Standard Time|Alaska standard time zone]]: (AKST; [[UTC-9]]; Zone V), which comprises most of the state of [[Alaska]]. * [[Hawaii-Aleutian Standard Time|Hawaii-Aleutian standard time zone]]: (or unofficially Hawaii Standard Time: HST) (HAST; [[UTC-10]]; zone W), which includes [[Hawaii]] and most of the length of the [[Aleutian Islands]] chain (west of 169°30′W). ===Zones outside the states=== *[[Atlantic Standard Time|Atlantic standard time zone]]: (AST; [[UTC-4]]; Zone Q), which comprises [[Puerto Rico]] and the [[U.S. Virgin Islands]]. *[[Samoa Time Zone|Samoa standard time zone]] (SST; [[UTC-11]]; Zone X), which comprises [[American Samoa]]. *[[Chamorro Time Zone|Chamorro standard time zone]]: (ChST; [[UTC+10]]; Zone K), which comprises [[Guam]] and the [[Northern Mariana Islands]]. == Boundaries between the zones == (Described from north to south along each boundary.) === EST/CST boundary === * roughly follows the border between [[Wisconsin]] (to west) and the [[Upper Peninsula of Michigan|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 (U.S. state)|Georgia]] (east) * divides most of the western [[Florida Panhandle|panhandle]] of Florida just west of [[Tallahassee, FL]] from the rest of the state. === 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]] bordering [[Colorado]] ([[Greeley County, Kansas|Greeley]], [[Hamilton County, Kansas|Hamilton]], [[Sherman County, Kansas|Sherman]] and [[Wallace County, Kansas|Wallace]] counties) from the rest of the state (three other counties which border [[Colorado]]—[[Cheyenne County, Kansas|Cheyenne]], [[Morton County, Kansas|Morton]] and [[Stanton County, Kansas|Stanton]]—observe CST) * follows the border between [[New Mexico]] (west) and [[Oklahoma]] (east) * follows the border between New Mexico (west) and [[Texas]] (east) * divides [[El Paso County, Texas|El Paso County]] and [[Hudspeth County, Texas|Hudspeth County]] from the rest of Texas === 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, Oregon|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) == Daylight saving time == {{seealso|Daylight saving time in the United States}} As an energy conservation measure, the [[Energy Policy Act of 2005]] extended [[daylight saving time|daylight saving time (DST)]] for an additional month beginning in 2007. The start of DST now occurs on the second Sunday in March and ends on the first Sunday in November. The Energy Policy Act specifies that continuation of daylight saving time beyond 2008 is subject to favorable evaluation of the energy savings attained. Unless the expanded DST period is rescinded, clocks will be set ahead one hour at 2 a.m. on the following start dates and set back one hour at 2 a.m. on these ending dates: {| class="wikitable" align="center" ! Year !! Start date !! Ending date |- |2006 || [[April 2]] || [[October 29]] |- |2007 || [[March 11]] || [[November 4]] |- |2008 || [[March 9]] || [[November 2]] |- |2009 || [[March 8]] || [[November 1]] |- |2010 || [[March 14]] || [[November 7]] |- |2011 || [[March 13]] || [[November 6]] |- |2012 || [[March 11]] || [[November 4]] |- |2013 || [[March 10]] || [[November 3]] |- |2014 || [[March 9]] || [[November 2]] |- |2015 || [[March 8]] || [[November 1]] |} 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 during the summer months. Originally this ran from the last Sunday in April until the last Sunday in October. Two subsequent amendments, in 1986 and 2005, have shifted these days so that daylight saving time now runs from the second Sunday in March until the first Sunday in November. [[Image:AZTZ.gif|thumb|right|128px|Arizona Time Zones]] * [[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|Hopi Nation]], which is [[Enclave and exclave|entirely surrounded]] by the Navajo Nation, does ''not'' observe DST. (See map inset right.) * 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, Ohio|Cincinnati]] and [[Louisville, Kentucky|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]] ==Notes== {{reflist}} ==See also== * [[History of time in the United States]] * [[Time in Indiana]] * [[List of U.S. states by time zone]] ==External links== *[http://aa.usno.navy.mil/faq/docs/us_tzones.php U.S. Navy time zone page] *[http://www.access.gpo.gov/nara/cfr/waisidx_03/49cfr71_03.html Standard Time Zone Boundaries 49CFR71] *[http://www4.law.cornell.edu/uscode/15/ch6schIX.html Standard Time Law 15USC260-267] *[http://www.time.gov/ The Official U.S. Time] [[Category:Time by country|United States]] [[Category:Geography of the United States]] [[de:Zeitzonen in den Vereinigten Staaten]] [[zh:美國時區]]