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A time zone is a region of the earth that has uniform standard time, usually referred to as the local time. By convention, time zones compute their local time as an offset from UTC (see also Greenwich Mean Time). Local time is UTC plus the current time zone offset for the considered location.
See the main article Time zone.
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Daylight saving time (DST; also summer time in British English; see Terminology) is the convention of advancing clocks so that afternoons have more daylight and mornings have less. Typically clocks are adjusted forward one hour near the start of spring and are adjusted backward in autumn. Modern DST was first proposed in 1907 by the English builder William Willett.<ref name=Prerau-3/> Many countries have used it since then; details vary by location and change occasionally.
The practice is controversial.<ref name=Downing-Prerau/> Adding daylight to afternoons benefits retailing, sports, and other activities that exploit sunlight after working hours,<ref name=Benfield/> but causes problems for farming, entertainment and other occupations tied to the sun.<ref name=farming/><ref name=Kissell/> Traffic fatalities are reduced when there is extra afternoon daylight;<ref name=Ferguson/> its effect on health and crime is less clear. Although an early goal of DST was to reduce evening usage of incandescent lighting, formerly a primary use of electricity,<ref name=Bartlett/> modern heating and cooling usage patterns differ greatly, and research about how DST currently affects energy use is limited and often contradictory.<ref name=Aries/>
DST's occasional clock shifts present other challenges. They complicate timekeeping and can disrupt meetings, travel, billing, recordkeeping, medical devices, and heavy equipment.<ref name=Neumann/> Many computer-based systems can adjust their clocks automatically, but this can be limited and error-prone, particularly when DST rules change.<ref name=Tong/>
Coordinated Universal Time (UTC,See National Institute of Standards and Technology Time and frequency FAQ, accessed 5 October 2008, for the origin of this abbreviation. Fr. Temps Universel Coordonné) is a time standard based on International Atomic Time (TAI) with leap seconds added at irregular intervals to compensate for the Earth's slowing rotation. Leap seconds are used to allow UTC to closely track UT1, which is mean solar time at the Royal Observatory, Greenwich.
The difference between UTC and UT1 cannot exceed 0.9 seconds, so if high precision is not required the general term Universal Time (UT) (without a suffix) may be used.
In casual use, Greenwich Mean Time (GMT) is used to mean either UTC or UT1. Owing to the ambiguity as to whether UTC or UT1 is meant, GMT is generally avoided in technical contexts.''Universal Time''. United States Naval Observatory. Retrieved on 1 February 2009.
Time zones around the world can be expressed as positive or negative offsets from UTC; UTC replaced GMT as the basis for the main reference time scale or civil time in various regions on January 1, 1972.
This is a list of time zones, sorted by time offsets from Coordinated Universal Time (UTC). Countries and regions observing the respective time zones are listed under it. This only gives current offsets. For more detailed and historic information, the zones must be divided. One list that does so is the tz database. See list of tz zones. Also see a helpful map (which is not necessarily completely up to date).
Regions marked with asterisks (* or **) observe daylight saving time: add one hour in summer (* for Northern Hemisphere summer; ** for Southern Hemisphere). Note, some locations use GMT (Greenwich Mean Time) instead of UTC (Coordinated Universal Time) in the definition of local time. For the purposes of this summary, the distinction is ignored.
Some zones north-south of each other in the mid Pacific differ by 24 hours in time: they have the same time of day but differ by a full day. The two extreme time zones on Earth (both in the mid Pacific) differ by 26 hours. A particular day starts earlier in countries with a more positive UTC offset. Thus the first occurrence of a date will be in UTC+14 and the last of the same date in UTC−12. This gives the interesting feature that during one hour each day there are three different dates in use on land around the world, e.g. at 10:30 UTC Monday it is already 00:30 Tuesday in the Line Islands (UTC+14) while the time is 23:30 Sunday in Samoa (UTC-11).
Time zone abbreviations are almost always customary, not legal—those listed here only exist in English and are somewhat arbitrary. English time zone names below generally only apply to English-speaking areas. The CIA and NAO disagree on the time kept by some Russian oblasts, so both are given below—this may be due to a recent time zone change.
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Standard time is the result of synchronizing clocks in different geographical locations within a time zone to the same time rather than using the local meridian as in local mean time or solar time. The time so set has come to be defined in terms of offsets from Universal Time. (See more about standard time.)
Where daylight saving time is used, "standard time" may refer to the time without daylight saving time.
Local mean time is a form of solar time that corrects the variations of local apparent time, forming a uniform time scale at a specific longitude. Its uniformity depends only on the accuracy of the clocks used to measure it.
Local mean time was used from the early nineteenth century, when local solar time or sundial time was last used, until standard time was adopted on various dates in the several countries. Standard time means that the same time is used throughout some region — usually, it was either offset from Greenwich Mean Time or was the local mean time of the capital of the region. The difference between local mean time and local apparent time is the equation of time.
The zoneinfo database, also called the tz database, is a collaborative compilation of information about the world's time zones, primarily intended for use with computer programs and operating systems. It is sometimes referred to as the Olson database after the founding contributor Arthur David Olson. Paul Eggert is editor and maintainer of the tz database.
Its most recognizable feature is the uniform naming convention designed by Paul Eggert for time zones, such as “America/New_York” and “Europe/Paris”. The database attempts to record historical time zones and all civil changes since 1970, the Unix time epoch. It also includes transitions such as daylight saving time, and even records leap seconds.
Solar times are measures of the apparent position of the Sun on the celestial sphere. They are not actually the physical time, but rather hour angles, that is, angles expressed in time units. They are also local times in the sense that they depend on the longitude of the observer.
Central European Time (CET) is one of the names of the time zone that is 1 hour ahead of Coordinated Universal Time. It is used in most European and some North African countries.
Its time offset is normally UTC+1. During daylight saving time, Central European Summer Time (CEST) is used instead (UTC+2). The current time offset is UTC+.
UTC+8 is a band of timezones separated from the Greenwich Mean Time by 8 hours.
UTC+8 is a possible candidate for ASEAN Common Time.
Terrestrial Time (TT) is the modern astronomical standard for the passage of time on the surface of the Earth (for civil purposes, Coordinated Universal Time (UTC) is standard). Since time moves at different rates for observers in different locations (due to relativity), and "the surface of the Earth" is not a single point in space, TT is a theoretical ideal; its measurement is approximated by the International Atomic Time (TAI) + 32.184 seconds.
In technical terms, TT is the proper time experienced by a clock located on the geoid. It is formally defined by its relationship to Geocentric Coordinate Time (TCG), which is the standard for the passage of time at the center of the Earth, used in astronomical calculations. In order to simplify calculations involving multiple astronomical bodies (each with their own gravity wells), TCG is defined as an approximation of time as it would pass without the relativistic effects of gravity; it therefore ticks by faster than TT.
There are eleven time zones in Russia from UTC+2 to UTC+12—more than in any other country of the world.
The time zones are as follows:
The only federal subjects to be in more than one time zone are the Sakha Republic, which is separated into areas which observe the Yakutsk, Vladivostok and Magadan time zones, and Sakhalin Oblast, which is in the Vladivostok (island Sakhalin) and Magadan time zones (Kuril Islands).
The two political entities currently using "China" as part of their official name, the People's Republic of China (PRC) (mainland China, Hong Kong, and Macau) and the Republic of China (ROC) (Taiwan) are in the same time zone which is eight hours ahead of the Coordinated Universal Time (UTC+8). In the past, this region had been divided into five time zones.
Although all jurisdictions within the region are placed under the same time zone, for historical and political reasons different jurisdictions keep their own time standard with their own names.
* In mainland China, the time standard is called the Beijing Time or Chinese Standard Time. A summer daylight saving time was observed from 1986 through 1991. * In Hong Kong, the standard is called Hong Kong Time. * In Macau, it is Macau Standard Time http://www.smg.gov.mo/geo/time_service/e_i_timeservice.htm. * In Taiwan, the time zone is Chungyuan Standard Time, although it is now also frequently referred to as Taipei Time.
Universal Time (UT) is a timescale based on the rotation of the Earth. It is a modern continuation of Greenwich Mean Time (GMT), i.e., the mean solar time on the meridian of Greenwich, and GMT is sometimes used loosely as a synonym for UTC. In fact the expression "Universal Time" is ambiguous, as there are several versions of it, the most commonly used being UTC and UT1 (see below). All of these versions of UT are based on sidereal time, but with a scaling factor and other adjustments to make them closer to solar time.
UTC+9 is a time zone used for the following locations:
The Alaska Time Zone observes standard time by subtracting nine hours from Coordinated Universal Time (UTC-9). During daylight saving time its time offset is only eight hours (UTC-8). The clock time in this zone is based on the mean solar time of the 135th meridian west of the Greenwich Observatory.
The zone includes nearly all of the U.S. state of Alaska and is one hour behind the Pacific Time Zone.
*standard time: Alaska Standard Time (AKST) *daylight saving time: Alaska Daylight Time (AKDT)
The western Aleutian Islands observe Hawaii-Aleutian Time, one hour behind the remainder of the state.
Effective 2007, the local time changes from AKST to AKDT at 02:00 LST to 03:00 LDT on the second Sunday in March and returns at 02:00 LDT to 01:00 LST on the first Sunday in November.
Time or UTC-11.
European Summer Time is the arrangement in Europe by which clocks are advanced by one hour in Spring to make the most of seasonal daylight. This is done in all of the countries of Europe except Iceland which observes Greenwich Mean Time (GMT) all year round. In the European Union this period extends from 01:00 GMT on the last Sunday in March until 01:00 GMT on the last Sunday in October each year. Europe is |0|not}} observing Summer Time today.This is automatically computed by the Mediawiki software by checking whether today's date falls within the interval specified by the above formulae.
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Standard time was introduced into Australia in the 1890s when all colonies adopted standard times. Before the switch to standard times, each local municipality was free to determine its own local time, called local mean time. Australia has three standard time zones from GMT: eastern (UTC+10), central (UTC+9:30) and western (UTC+8).Official government websitehttp://www.australia.gov.au/Time_Zones There are also some areas using an unofficial "central western" zone (UTC+8:45). Most Australian external territories also observe different time zones.
The proper names of Australia's time zones vary. In international contexts they are often called Australian Eastern Standard Time (AEST), Australian Central Standard Time (ACST), Australian Western Standard Time (AWST), and Australian Central Western Standard Time (ACWST). In domestic contexts the leading "Australian" is often dropped in speech though the abbreviations remain.
New South Wales (NSW), the Australian Capital Territory (ACT), Victoria (Vic), South Australia (SA), and Tasmania observe daylight saving time every year. Western Australia also observes daylight saving time on a trial basis. Queensland and Northern Territory do not have daylight saving.
Though each State and Territory has the sole responsibility in respect to time within its jurisdiction, the standard time within each State and Territory is set in relation to the "Co-ordinated Universal Time", which is determined by the International Bureau of Weights and Measures and maintained under section 8AA of the National Measurement Act 1960 of the Commonwealth.
This is a list of time zones as provided by the zoneinfo (or tz) database. It is derived from the 2008i edition of the zoneinfo software.
This table has the following columns: # ISO 3166-1 alpha-2 country code (c.c.). # Latitude and longitude of the zone's principal location in ISO 6709 +sign-degrees-minutes-seconds format, either ±DDMM±DDDMM or ±DDMMSS±DDDMMSS, first latitude (+ is north), then longitude (+ is east). # Zone name used in value of TZ environment variable. # Comments; present if and only if the country has multiple rows.
The table is sorted first by country, then an order within the country that (1) makes some geographical sense, and (2) puts the most populous zones first, where that does not contradict (1).[ftp://elsie.nci.nih.gov/pub/tzdata2008i.tar.gz zone.tab, timezone database], accessed January 3, 2009. NB: this file is in the public domain. The UTC offset is the standard offset, DST is not taken into account.
The Pacific Time Zone observes standard time by subtracting eight hours from Coordinated Universal Time (UTC-8). The clock time in this zone is based on the mean solar time of the 120th meridian west of the Greenwich Observatory. During daylight saving time, its time offset is UTC-7.
In the United States and Canada, this time zone is generically called Pacific Time (PT). Specifically, it is Pacific Standard Time (PST) when observing standard time (Winter), and Pacific Daylight Time (PDT) when observing daylight saving time (Summer). Canada follows United States daylight time. In Mexico the UTC-8 time zone is known as the Northwest Zone (Zona Noroeste), which formerly was synchronized with the U.S. PDT daylight saving schedule.
The zone is one hour ahead of the Alaska Time Zone, one hour behind the Mountain Time Zone and three hours behind the Eastern Time Zone.
UTC+2 corresponds to the following time zones:
The Samoa Time Zone observes standard time by subtracting eleven hours from Coordinated Universal Time (UTC-11). The clock time in this zone is based on the mean solar time of the 165th meridian west west of the Greenwich Observatory.
The zone includes the U.S. territory of American Samoa, as well as the Midway Islands and the uninhabited islands of Jarvis, Palmyra, and Kingman Reef.
The zone is one hour behind Hawaii-Aleutian Time Zone, one hour ahead of Howland and Baker Islands, and 23 hours behind Wake Island Time Zone.
Starting in 2009, Samoa will use Daylight Saving Time from the first Sunday in October until the last Sunday in March. During this period, Samoa will be on UTC-10.
The Mountain Time Zone of North America keeps time by subtracting seven hours from Coordinated Universal Time, sometimes called Greenwich Mean Time (UTC-7) during the shortest days of autumn and winter, and by subtracting six hours during daylight saving time in the spring, summer, and early autumn (UTC-6). The clock time in this zone is based on the mean solar time of the 105th meridian west of the Greenwich Observatory.
In the United States and Canada, this time zone is generically called Mountain Time (MT). Specifically, it is Mountain Standard Time (MST) when observing standard time (Winter), and Mountain Daylight Time (MDT) when observing daylight saving time. In Mexico this time is known as the Pacific Zone. In the USA, the exact specification for the location of time zones and the dividing line between zones is set forth in the Code of Federal Regulations at 49 CFR 71.The specification for the Mountain Time Zone is set forth at 49 CFR 71.8, and is listed in Text and pdf formats.<br />The boundary between Central and Mountain is set forth at 49 CFR 71.7, and is listed in text and pdf formats. The boundary between Mountain and Pacific is set forth at 49 CFR 71.9, and is listed in text and pdf formats.
The zone is one hour ahead of the Pacific Time Zone and one hour behind the Central Time Zone.
In some areas, starting in 2007, the local time changes from MST to MDT at 02:00 LST to 03:00 LDT on the second Sunday in March and returns at 02:00 LDT to 01:00 LST on the first Sunday in November.
TV broadcasting in the Mountain Time Zone is typically tape-delayed one hour, so that shows match the broadcast times of the Central Time Zone (i.e. prime time begins at 7:00 p.m. MT following the same order of programming as the other two time zones).
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UTC+1 is used in the following locations:
* Central European Time * West Africa Time * Western European Summer Time* ** British Summer Time* ** Irish Summer Time* * Romance Standard Time (Microsoft Windows Control panel) * Swatch Internet Time
Daylight saving time around the world, showing usage and a short history by location in alphabetic order.
Canada is divided into six time zones and ranks third among countries with respect to number of time zones, after Russia (eleven) and the United States (nine).
Times used (* indicates use of daylight saving time):
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A time offset is defined by international convention as a number of hours and minutes from Coordinated Universal Time (GMT, approximately). Many time zones employ two time offsets, one for standard time and one for daylight saving time.
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Central European Summer Time (CEST) is one of the names of UTC+2 time zone, 2 hours ahead of Coordinated Universal Time. It is used as a summer daylight saving time in most European and some North African countries. During the winter, Central European Time (UTC+1) is used.
Central European Summer Time used to be also known under other names, such as Middle European Summer Time (MEST), Central European Daylight Saving Time (CEDT) or 'Bravo time', after the 2nd letter of the phonetic alphabet. Note that CEST is commonly referred to as CET.
Time in the United States, by law, is divided into nine standard time zones 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 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.
China standard time or Beijing time is the time zone observed in the People's Republic of China (PRC). It is eight hours ahead of UTC (UTC+8).
Certain regions of eastern Asia, including Greater China, also observe time zones which have the same offset, but use different names, such as Chungyuan Standard Time, Philippine Standard Time, Singapore Standard Time, etc.
The PRC observed daylight saving time from 1986 through 1991, but does not now.
The Central Time Zone is in the Americas and observes standard time by subtracting six hours from UTC during standard time (UTC−6) and five hours during daylight saving time (UTC−5). The clock time in this zone, comprised almost totally of a strip of territory in North America, is based on the mean solar time of the 90th meridian west of the Greenwich Observatory.
In the United States and Canada, this time zone is generically called Central Time (CT). Specifically, it is Central Standard Time (CST) when observing standard time (Winter), and Central Daylight Time (CDT) when observing daylight saving (Summer). In Mexico this time is known as the Central Zone.
The zone is two hours ahead of the Pacific Time Zone, one hour ahead of the Mountain Time Zone, and one hour behind the Eastern Time Zone.
Moscow Time () is the time zone for the city of Moscow, Russia and most of western Russia, including Saint Petersburg. It is the second westernmost of the 11 time zones of Russia.
During the winter, between the last Sunday of October and the last Sunday of March, Moscow Standard Time (MSK, МСК) is 3 hours ahead of UTC, or UTC+3. During the summer, Moscow Time shifts forward an additional hour ahead of Moscow Standard Time to become Moscow Summer Time (MSD), making it UTC+4.
In accordance with the 16 June 1930 Decree of the Council of People's Commissars, the Decree Time was introduced by adding one hour to the time in each time zone of the USSR, so that Moscow Time became three hours ahead of Coordinated Universal Time.
Moscow Time is in use for scheduling trains, airplanes, ships, etc. throughout the Russian Federation, this time is registered in telegrams, etc. Times in Russia are often announced throughout the country on radio stations as Moscow Time.
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Korea Standard Time (KST, Korean: Han-guk pyojunsi) is the standard time zone in North and South Korea and is 9 hours ahead of UTC (UTC+9): i.e., when it is midnight (00:00) UTC, it is 9 am (09:00) Korea Standard Time. Korea does not currently observe daylight saving time but has experimented with it in the past.When is daylight saving time worldwide?<!-- Bot generated title -->South Korea time changes Korea Standard Time is the same as Japan Standard Time, Indonesian Eastern Standard Time and Yakutsk Time.
UTC−12 is a nautical time zone comprising the high seas between 180° and 172°30′W longitude. Subtract twelve hours from Coordinated Universal Time to obtain the time for this zone. Ships using this time are the last to begin each calendar day. No human habitations are in this time zone. Uninhabited Baker Island and Howland Island are the only landmasses in this time zone.
UTC+5:45 is used in:
The United Kingdom uses Greenwich Mean Time (UTC) and British Summer Time (UTC+1).
The UK used Local Mean Time until railway timetabling gradually established the two standards of Greenwich Mean Time and Dublin Mean Time (UTC-0:25). These were legally adopted in 1880. In 1916, Greenwich Mean Time was introduced to Ireland, and British Summer Time was introduced.
At the beginning of the 20th century Sandringham Time (UTC+0:30) was used by the royal household.
The United Kingdom experimentally adopted Central European Time in the years 1968–71; however, this experiment proved unpopular and short-lived, mainly due to the increased number of road accidents (many involving children walking to school) in the dark winter mornings.
Regulation of time zones and Summer Time is a reserved matter, meaning that only in the Parliament of the United Kingdom has power to legislate, rather than devolved administrations such as the Scottish Parliament.
The Daylight Saving Act of 1917 was an act enacted by the Dominion of Newfoundland to adopt daylight saving time (DST), thus making it one of the first jurisdictions in North America to do so, only a year after Britain itself on May 21 1916. DST was not instituted in the United States until March 31, 1918.
Nepal Time (NPT) is the time zone for Nepal. It is UTC+5:45, and is one of only two time zones without an hour or half-hour offset from UTC. Chatham Islands (offshore islands of New Zealand) is the only other place with such time zone. Its time zone is UTC+12:45. See Chatham Standard Time Zone
UTC+4:30 is used in:
The time correction DUT1 (sometimes also written DUT) is the difference between Universal Time (UT1), which is defined by Earth's rotation, and Coordinated Universal Time (UTC), which is defined by a network of precision clocks.
:DUT1 = UT1 − UTC
UTC is maintained via leap seconds, such that DUT1 remains within the range −0.9 s < DUT1 < +0.9 s. The reason for this correction is that the rate of rotation of the Earth is not constant, due to tidal braking and the redistribution of mass within the Earth, including its oceans and atmosphere.
Forecast values of DUT1 are published by IERS Bulletin A. Weekly updated values of DUT1 with 0.1 s precision are broadcast by several time signal services, including WWVB.
The Province of Saskatchewan observes Central Standard Time but, since it is geographically located in the Mountain Time Zone, is effectively on daylight saving time year round.
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UTC+3 is used in the following locations:
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The history of Chatham Islands numismatics begins in 1999, when the Reserve Bank of New Zealand authorized a private organization, the Chatham Islands Note Corporation, to issue banknotes to celebrate that the Chatham Islands would have been the first land to enter the third millennium of the common era (although this is not actually true - this honour belongs to Antarctica. The first island to enter the third millennium would be Millennium Island).
The Reserve Bank of New Zealand gave this authorization under the condition that such notes cannot be declared legal tender. In other words, these notes were to be used for payment, but only if the seller accepted them: there was no obligation for anyone to accept the notes issued by the Chatham Islands, contrarily to the notes issued by the Reserve Bank of New Zealand. These Chatham Islands notes were generally accepted by merchants on the Chatham Islands.
The Chatham Islands Note Corporation was initially based in Christchurch, in the South Island of New Zealand. The agent for providing the notes to the numismatic trade was Leon Morel, FRNSNZ of Melbourne, Victoria (Australia). The Chatham Islands Note Corporation later shifted their base of operations to Waitangi, Chatham Islands.
The Chatham Islands dollar (Ch.I.$) was pegged at the same rate as the New Zealand dollar.
The Newfoundland Time Zone (NT) is a geographic region that keeps time by subtracting 3½ hours from Coordinated Universal Time (UTC), resulting in UTC-3:30, or 2½ hours during daylight saving time. The clock time in this zone is based on the mean solar time of the 52nd degree and 30 arcminute meridian west of the Greenwich Observatory. NT is used only in Canada, and there only by the province of Newfoundland and Labrador. Officially, the entire province is in the Newfoundland Time Zone by legislation.http://www.assembly.nl.ca/legislation/sr/statutes/s23.htm In practice, however, it is observed only on the island of Newfoundland, its offshore islands, and southeastern Labrador communities south of Black Tickle. The rest of Labrador, from Cartwright north and west, observes Atlantic Standard Time. Southeastern Labrador prefers Newfoundland Time in part to synchronize with the schedule of radio broadcasts from Newfoundland.
This unique time zone exists because of the location of the island and the fact that it was a separate dominion when the time zones were established. The island of Newfoundland lies squarely in the eastern half of the Atlantic Standard Time Zone, exactly three and a half hours from Greenwich and, as a separate dominion, it had the ability to adopt its own timezone. However the entire province lies west of the standard meridian for a half-hour time zone, 52.5 degrees west longitude. In 1963, the Newfoundland government attempted to bring the province into conformity with the other Atlantic provinces, but withdrew in the face of stiff public opposition.http://wwp.greenwichmeantime.com/time-zone/north-america/canada/newfoundland/index.htm
Daylight saving time is observed throughout the province. In 1988 the provincial government experimented with double daylight saving time, moving clocks ahead two hours during daylight saving time instead of just one. This move proved unpopular in the fall when children started going to school in the dark. In 2006, the province enacted an extension to daylight saving time,http://www.assembly.nl.ca/legislation/sr/statutes/s23.htm starting in 2007, following the lead of the United States and other Canadian provinces.
This unusual time zone puts the island of Newfoundland an hour and a half ahead of Central Canada, a half hour ahead of New Brunswick, Nova Scotia, Prince Edward Island, and half an hour behind Saint-Pierre and Miquelon. Because of this, it will hit milestones of time before (almost) any other part of the continent, a quirk that draws attention to Newfoundland. For instance the Newfoundland release of Harry Potter and the Half-Blood Prince and Halo 2 was publicized across Canada.
Likewise, in the case of Canada-wide broadcasts timed to be heard at the same hour in the rest of the country through the use of a different feed for each time zone, Newfoundland uses Atlantic-time broadcasts, so references to programs being at "six o'clock, six-thirty in Newfoundland" are commonly heard across Canada. However, a station in St. John's originating local programming may refer to it as "coming up at six-thirty, six o'clock in Labrador".
UTC+5 is the timezone for:
ASEAN Common Time is an idea by ASEAN to adopt a standard time of UTC+8 for all member countries. Some businesses with a local or regional reach have already adopted the use of the "ASEAN Common Time", and can be seen using the abbreviation '"ACT"' in their Press Releases, communications, and legal documents. There are also ASEAN Citizens who have started using ACT in their sites and blogs.
time zones used by ASEAN countries are UTC+6:30, UTC+7, UTC+8 and UTC+9.
* UTC+7, UTC+8, UTC+9, see Time in Indonesia * UTC+8 * UTC+8, Peninsular Malay switched from UTC+7:30 on 1982-01-01, see Time in Malaysia, East Malaysia since 1933 except for Jap. occupation. * UTC+8 * UTC+8, since 1982-01-01, see Time in Singapore * UTC+7 * UTC+7 * UTC+7, tried to switch in 2001, see Time in Thailand * UTC+7 * UTC+6:30
The observers use * UTC+9 * UTC+10
Non-ASEAN members of ASEAN Plus Three * UTC+8 * UTC+9 * UTC+9
The Atlantic Standard Time Zone (AST) is a geographical region that keeps time by subtracting four hours from either Coordinated Universal Time (UTC) or Greenwich Mean Time (GMT), resulting in UTC-4 or GMT-4. The clock time in this zone is based on the mean solar time of the 60th meridian west of the Greenwich Observatory.
In Canada, the provinces of New Brunswick and Nova Scotia reckon time specifically as an offset of 4 hours from Greenwich Mean time (GMT-4). (UTC is regularly adjusted by means of leap seconds to keep it synchronized to within 1 second of GMT.) Prince Edward Island and small portions of Quebec (eastern Côte-Nord and the Magdalen Islands) are also part of the Atlantic Standard Time Zone. Officially, the entirety of Newfoundland and Labrador observes Newfoundland Standard Time, but in practice most of Labrador uses the Atlantic Standard Time Zone.
Other parts of the world that keep time by subtracting four hours from UTC include Bermuda, in the North Atlantic; many Caribbean islands, including Puerto Rico, the US Virgin Islands; and several South American countries, such as Paraguay, Chile, Bolivia, and parts of Brazil. Venezuela used AST until December 9, 2007, when it switched to UTC-4:30.
AST is known (where applicable) as Atlantic Daylight Time (ADT) during daylight saving time, and has one hour added to make it three hours behind GMT (UTC-3).
Decree time () refers to the changes introduced to the USSR time system by a Sovnarkom decree of 16 June 1930. By this decree, all clocks in the Soviet Union were permanently shifted one hour ahead of standard time for each timezone.
It is independent from Daylight Saving Time, which was introduced in the USSR much later, in 1981. In fact, with both time shifts in effect, summer time was two hours ahead of standard time in the USSR.
From 1982 to 1986, decree time was gradually abolished by the USSR government in 30 oblasts and autonomous Republics of the Russian SFSR. In 1990, it was further abolished in Ukraine, Moldavia, Georgia and Azerbaijan, followed by the entire territory of the Soviet Union in March 1991 (eight months before its dissolution).
On 23 October 1991, the Supreme Soviet of the Russian SFSR ruled to restore decree time in Russia. It was restored on 19 January 1992, except for the following federal subjects: *Astrakhan Oblast *Kirov Oblast *Novosibirsk Oblast *Samara Oblast *Saratov Oblast *Udmurtia *Volgograd Oblast
Indian Standard Time (IST) is the time observed throughout India and Sri Lanka, with a time offset of UTC+5:30. India does not observe daylight saving time, (DST) or other seasonal adjustments, although DST was used briefly during the Sino–Indian War of 1962 and the Indo–Pakistani Wars of 1965 and 1971.<ref name="timez"> </ref> In military and aviation time, IST is designated E* ("Echo-Star").
Indian Standard Time is calculated on the basis of 82.5° E longitude, which is just west of the town of Mirzapur, near Allahabad in the state of Uttar Pradesh.<ref name="two-timing"></ref> The longitude difference between Mirzapur and the United Kingdom's Royal Observatory at Greenwich translates to an exact time difference of 5 hours 30 minutes. Local time is calculated from a clock tower at the Allahabad Observatory () though the official time-keeping devices are entrusted to the National Physical Laboratory, in New Delhi.<ref name="bbc"></ref>
Hong Kong Time (abbreviation: HKT ; ) is the time in Hong Kong. The time is UTC+8 all year round. Owing to the longitude in which Hong Kong is located, HKT is in the same time zone as used by the time standards in the rest of the People's Republic of China - Chinese Standard Time (also known as Beijing Time or Beijing Standard Time) in mainland China, and Macau Standard Time in Macau.
From 1941 to 1979, Hong Kong adopted daylight saving measures, but in 1980 the government found these unnecessary as Hong Kong is at a relatively low latitude, and decided to eliminate the practice.
Greenwich Mean Time was adopted as the basis in 1904, and UTC was adopted as a standard in 1972. Before that, local time was determined by astronomical observations at the Hong Kong Observatory using a 6-inch Lee Equatorial and a 3-inch Transit Circle.
The Chatham Islands Note Corporation was the private organisation that was set up to issue the two series of Chatham Islands notes in 2000 and 2001. It planned to issue coins in 2001, but their activities were curtailed upon the instruction of the Reserve Bank of New Zealand. The Chatham Islands Note Corporation ceased to operate some time in 2003.
Singapore uses a time zone eight hours in advance of UTC, (UTC+8). It is known as Singapore Standard Time or SST, and is the same as Australian Western Standard Time, Central Indonesia Time, Malaysian Standard Time, Philippine Standard Time, Chinese Standard Time, Hong Kong Time and Macau Standard Time.
The British Columbia time referendum, 1972 was a referendum held in British Columbia on August 30, 1972, simultaneously with a general election. The actual referendum only took place in four electoral districts and part of a fifth, all located in the northeast or southeast parts of the province. The purpose of the vote was to determine which areas favoured following Mountain Time rather than Pacific Time and whether to follow daylight saving time or not. All areas chose to follow Mountain Time.
In Indonesia, the keeping of standard time is divided into three time zones: *Indonesian Western Standard Time (Indonesian: Waktu Indonesia Barat/WIB) (UTC+7) **WIB is observed in islands of Sumatra, Java, provinces of West Kalimantan and Central Kalimantan *Indonesian Central Standard Time (Waktu Indonesia Tengah/WITA) (UTC+8) **WITA is observed in islands of Sulawesi, Bali, provinces of East Nusa Tenggara, West Nusa Tenggara, East Kalimantan and South Kalimantan *Indonesian Eastern Standard Time (Waktu Indonesia Timur/WIT) (UTC+9). **WIT is observed in provinces of Maluku, North Maluku, Papua and West Papua.
Philippine Standard Time (, abbreviated PST) or Philippine Time (abbreviated PHT), is the name used in the Philippines to describe its location among the world's time zones. Modern Philippine Standard Time was instituted through Batas Pambansa Blg. 8, the law defining the metric system, which was approved on December 2, 1978 and implemented on January 1, 1983.
Geographically, the Philippines lies within 116°40′ and 126°34′ east of the Prime Meridian, and as such is physically located within the UTC+8 time zone. Philippine Standard Time is maintained by the Philippine Atmospheric, Geophysical and Astronomical Services Administration, or PAGASA. The Philippines shares the same timezone with Hong Kong, Macau, Singapore, most parts of China, Taiwan, Malaysia, Brunei, central Indonesia and Western Australia.
In the 1990s, due to frequent power outages, daylight saving time was instituted. As the Philippine power supply and transmission systems recovered, daylight saving time was ended, and is presently not in use.
Macau Standard Time () is the time in Macau. The time is UTC+8 all year round, and daylight saving time is not applied. Macau Standard Time is in the same time zone as China Standard Time, also known as Beijing Standard Time or simply Beijing Time in mainland China, and Hong Kong Time in Hong Kong.
Yekaterinburg Time (YEKT) is the time zone 5 hours ahead of UTC (UTC+5) and 2 hours ahead of Moscow Time (MSK+2). Yekaterinburg Summer Time (YEKST) is UTC+6, but remains constant as regards Moscow Time (MSD+2). YEKT/YEKST is the official time zone for Bashkortostan, Perm Krai, Kurgan Oblast, Orenburg Oblast, Sverdlovsk Oblast, Tyumen Oblast, Chelyabinsk Oblast, Khanty-Mansi Autonomous Okrug and Yamalo-Nenets Autonomous Okrug.
Main cities: *Yekaterinburg *Kurgan *Perm *Tyumen *Ufa *Chelyabinsk
This is a list of United States of America States by time zone. For more about the time zones of the U.S. and other time zones see time in the United States and time zone.
Krasnoyarsk Time (KRAT) is the time zone 7 hours ahead of UTC (UTC+7) and 4 hours ahead of Moscow Time (MSK+4). Krasnoyarsk Summer Time (KRAST) is UTC+8, but remains constant as regards Moscow Time (MSD+4). KRAT/KRAST is the official time zone for Kemerovo oblast (Western Siberian region), Krasnoyarsk Krai, and most other Eastern Siberian regions in Russia. Previously known as Novosibirsk Time (NOVT/NOVST), in 1993 Novosibirsk Oblast changed time zones and since then has used Omsk Time (MSK+3/MSD+3), thus requiring a new name for the time zone.
The Chamorro Time Zone"Chamorro" per as amended and 49 CFR 71.14 (text, PDF)., formerly the Guam Time Zone, observes standard time by adding ten hours to Coordinated Universal Time (UTC+10). The clock time in this zone is based on the mean solar time of the 150th meridian east of the Greenwich Observatory.
The zone includes the U.S. territories of Guam and the Northern Mariana Islands. Daylight Saving Time is not observed anywhere in the zone. Because the original inhabitants of the region are Chamorro, the time in this zone is always known as Chamorro Standard Time (ChST).
The zone is two hours behind Wake Island Time Zone, 15 hours ahead of North American Eastern Time Zone, and 18 hours ahead of Pacific Time Zone.
Chamorro Standard Time is practically the same time as Australian Eastern Standard Time.
Port Blair mean time was the time zone of the Andaman and Nicobar Islands of India in the Bay of Bengal. The time zone was set up during the early 1800s remained in effect until January 1, 1906 as the Indian Standard Time became the official time of India.
Calcutta time was one of the two time zones established in British India in 1884. It was established during the International Meridian Conference held at Washington, D.C in the United States. It was then decided that India were to have two time zones, with Calcutta (now Kolkata) would use the 90th east meridian and Bombay (Mumbai) the 75th east meridian. Calcutta time was set at 5 hours, 30 minutes, and 21 seconds in advance of GMT.
It remained in effect even after Indian Standard Time (IST) was adopted on January 1, 1906. In 1948, Calcutta time was completely abandoned in favour of IST.
The Chatham Standard Time Zone is a geographic region that keeps time by adding twelve hours and forty-five minutes to Coordinated Universal Time (UTC) resulting in UTC+12:45.
The Chatham Standard Time Zone is used exclusively in the Chatham Island Group, a territory of New Zealand, located in the South Pacific Ocean at 43°53′54″S, 176°31′44″W.
The Yukon Standard Time Zone (YST) was a geographic region that kept standard time by subtracting nine hours from Coordinated Universal Time (UTC) resulting in UTC−9 after 1971, or from Greenwich Mean Time (GMT) before 1972.
It included the Yukon in Canada, as well as a small region around Yakutat, Alaska (Alaska had been spread across four different time zones at the time). However, in 1975, the Yukon officially switched to Pacific Time zone (PST), which is UTC−8. Moreover, Alaska switched in 1983 from four time zones to two time zones, placing most of the state in Alaska Standard Time Zone (AKST), the time zone formerly known as Yukon Standard Time Zone, while the Aleutian Islands remained in the Hawaii-Aleutian Standard Time Zone (until 1983 known as the Alaska-Hawaii Standard Time Zone).
Yukon Standard Time Zone is the same as Alaska Standard Time Zone. The only difference is that the name of the time zone was officially changed from Yukon Standard Time Zone to Alaska Standard Time Zone following the Alaska switch from four different time zones to predominantly UTC−9 in 1983.
Uzbekistan Time is the standard timezone in Uzbekistan that 5 hours ahead of UTC. The standard time uses no daylight saving time, though there has been constant debate whether to adopt it in order to increase leisure time.
Prior to the breakup of the Soviet Union there were two time zones in Uzbekistan. In the Soviet era most time zones were daylight time in the winter and double daylight time in the summer. The western part of the country observed Samarkand Time 5 or 6 hours ahead of UTC.http://www.timeanddate.com/worldclock/timezone.html?n=386&syear=1990 The eastern part observed Tashkent Time 6 or 7 hours ahead of UTC.http://www.timeanddate.com/worldclock/timezone.html?n=244&syear=1990 In 1991 the clocks did not move forward in the spring to maintain single daylight time only in the summer. That fall a unified time zone was adopted 5 hours ahead of UTC.
The Wake Island Time Zone observes standard time by adding twelve hours to Coordinated Universal Time (UTC+12). The clock time in this zone is based on the mean solar time of the 180th degree meridian east of the Greenwich Observatory.
The zone includes the U.S. territory of Wake Island and is two hours ahead of Chamorro Time Zone, 23 hours ahead of Samoa Time Zone, and 24 hours ahead of Howland and Baker Islands.
UTC+5:40 was a sometimes used as approximation for Nepal Time, which until 1986 was based on Kathmandu mean time, which is at 85°19'E or 5:41:16.
Since 1986 Nepal Time is UTC+5:45.
The Hawaii-Aleutian Time Zone observes Hawaii-Aleutian Standard Time (HST), by subtracting ten hours from Coordinated Universal Time (UTC-10). The clock time in this zone is based on the mean solar time of the 150th meridian west of the Greenwich Observatory.
The zone also includes Alaska's Aleutian Islands west of 169° 30′ west, along with Hawaii. The portion in the Aleutian islands observes DST while Hawaii does not.
Hawaii used a standard time of GMT-10:30 from 1900 until 1947, when clocks were changed to the present -10:00 zone. http://www.twinsun.com/tz/tz-link.htm
[Abstract not available for the category]
Chatham Island is by far the largest island of the Chatham Islands group, in the south Pacific Ocean off the eastern coast of New Zealand, — not exactly "halfway between the equator and the pole, and right on the International Date Line" but close enough for tourism marketing purposes. Chatham Island was named after the survey ship HMS Chatham which was the first European ship to locate the island in 1791 . It covers an area of .
The island is also known by two other names, the Maori name of Wharekauri and the Moriori name of Rekohu (meaning misty skies).
The geography of the roughly T-shaped island is dominated by three features: two bays and a lagoon. More than half of the west coast of Chatham is taken up by the deep indentation of Petre Bay. The island's main settlement of Waitangi is located in a small indentation in Petre Bay's southern sage.
On the east coast is the even larger Hanson Bay, which stretches for the entire length of the island.
The ten kilometre width of the island, between these two bays, is entirely illusory. Much of it is taken up by the large Te Whanga Lagoon, which drains to the sea in the southern half of Hanson Bay. This lagoon covers about , and drains several small rivers that rise in the hills at the south end of the island.
Eastern European Summer Time (EEST) is one of the names of UTC+3 time zone, 3 hours ahead of Coordinated Universal Time. It is used as a summer daylight saving time in some European, North African, and Middle Eastern countries. During the winter, the Eastern European Time (UTC+2) is used.
UTC+0:30 was used in the British royal household, and is known as Sandringham time. It was stopped in 1936.
It was also used in Switzerland (Bernese Time) until the adoption of Central European Time in 1894.
Mexico uses three different UTC offsets as defined in the federal Law of Time Systems:National Commission for the Conservation of Energy http://www.conae.gob.mx/work/sites/CONAE/resources/LocalContent/4634/5/Leyhorario.pdf
*Zone 1 (Central Zone) covers most of Mexico and is equivalent to UTC-6 (the equivalent of Canadian and U.S. Central Time Zone). *Zone 2 (Pacific Zone) covers the states of Baja California Sur, Chihuahua, Nayarit, Sinaloa, and Sonora, which use UTC-7 (the equivalent of Canadian and U.S. Mountain Time Zone). *Zone 3 (Northwest Zone) covers the state of Baja California and uses UTC-8 (the equivalent of Canadian and U.S. Pacific Time Zone).
In addition, the law dictates that all island territories should fall within the time zone corresponding to their geographic location.
#redirect Thai six-hour clock
Germany uses Central European Time (Mitteleuropäische Zeit, MEZ; UTC+1) and Central European Summer Time (Mitteleuropäische Sommerzeit, MESZ; UTC+2). Daylight saving time is observed from the last Sunday in March (02:00 CET) to the last Sunday in October (03:00 CEST). The doubled hour during the switch back to standard time is named 2A (02:00 to 03:00 CEST) and 2B (02:00 to 03:00 CET).
Germany has the single zoneinfo zone "Europe/Berlin", although in 1945, the Trizone did not follow Berlin's switch to midsummer time.
UTC+7:30 was used both as daylight saving time as well as its Standard Time later in Singapore. Between 1941 and 1942 before the Japanese occupation, and from 1945 to 1970 after the occupation, Singapore used UTC+7:30 as its daylight saving time. It was later in 1970 that Singapore decided declare UTC+7:30 as its Singapore Standard Time.
UTC+8 is the current Singapore Standard Time and this time standard has been in use since 1982.
UTC+7:20 was used as daylight saving time in Singapore between 1933 and 1940.
Brazil has three time zones. Daylight saving time (summer time) is also observed by the Southern, Southeast and Central-Western Brazilian states.
Central European Midsummer Time (CEMT) is one of the names of UTC+3 time zone, 3 hours ahead of Coordinated Universal Time. It was used as a double summer daylight saving time in several European countries during the 1940s.
[Abstract not available for the category]
The establishment of nautical standard times, nautical standard time zones and the nautical date line were recommended by the Anglo-French Conference on Time-keeping at Sea in 1917. The Conference recommended that the standard apply to all ships, both military and civilian. These zones were adopted by all major fleets between 1920 and 1925 but not by many independent merchant ships until World War II.
The nautical time zone system is an ideal form of the terrestrial time zone system for use on high seas. Under the system time changes are required for changes of longitude in one-hour steps. The one-hour step corresponds to a time zone width of 15° longitude. The 15° gore that is offset from GMT or UT1 (not UTC) by twelve hours is bisected by the nautical date line into two 7.5° gores that differ from GMT by ±12 hours. A nautical date line is implied but not explicitly drawn on time zone maps. It follows the 180th meridian except where it is interrupted by territorial waters adjacent to land, forming gaps: it is a pole-to-pole dashed line.
Time on a ship's clocks and in a ship's log had to be stated along with a "zone description", which was the number of hours to be added to zone time to obtain GMT, hence zero in the Greenwich time zone, with negative numbers from −1 to −12 for time zones to the east and positive numbers from +1 to +12 to the west (hours, minutes, and seconds for nations without an hourly offset). These signs are opposite to those given below because ships must obtain GMT from zone time, not zone time from GMT. All zones were pole-to-pole staves 15° wide, except −12 and +12 which were each 7.5° wide, with the 180° meridian separating them. Unlike the zig-zagging land-based International Date Line, the nautical International Date Line follows 180° except where it is interrupted by territorial waters and the lands they border, including islands.
Around 1950, a letter suffix was added to the zone description, assigning Z to the Zero Zone, and A–M (except J) to the east and N–Y to the west (J may be assigned to local time in non-nautical applications; zones M and Y have the same clock time but differ by 24 hours: a full day). These were to be vocalized using a phonetic alphabet which pronounces the letter Z as Zulu, leading sometimes to the use of the term "Zulu Time". The Greenwich time zone runs from 7.5°W to 7.5°E longitude, while zone A runs from 7.5°E to 22.5°E longitude, etc.
These nautical letters have been added to some time zone maps, like the map of Standard Time Zones by Her Majesty's Nautical Almanac Office (NAO), which extended the letters by adding an asterisk (*) or dagger (†) for areas that do not use a nautical time zone, and a double dagger (‡) for areas that do not have a legal standard time (Greenland's ice sheet and all of Antarctica. The United Kingdom specifies UTC−3 for the Antarctic Peninsula, but no other country recognizes that). They conveniently ignore any zone that does not have an hour or half-hour offset, so a double dagger (‡) has been co-opted for these zones in the list of time zones.
In maritime usage, GMT retains its historical meaning of UT1, the mean solar time at Greenwich. UTC, atomic time at Greenwich, is too inaccurate, differing by as much as 0.9 s from UT1, creating an error of 0.4 km in longitude at the equator. However, DUT can be added to UTC to correct it to within 50 ms of UT1, reducing the error to only 20 m.
A ship is required to adopt the standard time of a country when it is in its territorial waters, but must revert to nautical time as soon as it leaves territorial waters.
In reality nautical times are used only for radio communication etc. Internally on the ship, e.g. for work and meal hours, the ship may use a suitable time of its own choosing. The captain is permitted to change his ship's clocks at a time of his choice following his ship's entry into another time zone — he often chose midnight. Long distance going ships change time zone onboard at suitable times. Ships on short distance journeys do not change time zone at all, even if they go between different time zones, like between the UK and the continent. Passenger ships often use both time zones on signs. In time tables and communication with land, the land time zone has to be used.
For airplanes similar principles are used.
Bombay time was one of the two official time zones established in British India in 1884. The time zone was established during the International Meridian Conference held at Washington, D.C in the United States in 1884. It was then decided that India would have two time zones, with Calcutta (now Kolkata) using the 90th east meridian and Bombay (now Mumbai) the 75th east meridian. Bombay time was set at 4 hours and 51 minutes ahead of Greenwich Mean Time (GMT).
Bombay time however faced difficulties in converting to Indian Standard Time (IST) after that was adopted on 1 January 1906 as the official time zone of India. During the same time period in Mumbai, Bal Gangadhar Tilak, a prominent freedom fighter of the Indian independence movement was put on trial in a bomb blast case. With public sentiment against the government, prominent barrister Pherozeshah Mehta fervidly argued against the time change. He managed to stall proceedings in the Bombay Municipal Corporation for a few days by arguing that the government did not take the people into confidence. Faced with rising public resentment over the trial, the government shelved the conversion, and Bombay time was maintained until 1955.
Thailand uses the UTC+7 time zone, with no observation of daylight saving time. The abbreviation for Thailand Standard Time is "THA".
In 2001,Why is Singapore in the “Wrong” Time Zone?<!-- Bot generated title --> then-Prime Minister Thaksin Shinawatra announced intentions to change the country's time zone to UTC+8 to be in line with Singapore, Malaysia, China, Hong Kong. This was met with much criticism and resistance. The plan was later withdrawn.
Although the Chatham Islands are constitutionally part of New Zealand, the Chatham Islands did issue numismatic items prior to the banknote issues of 2000 and 2001 in the form of postal notes and postal orders.
Washington mean time was the time at the meridian through the center of the old dome atop the main building at the old US Naval Observatory at Washington, D.C. This Washington meridian was defined on 28 September 1850 by the United States Congress (9 Stat. 515). The Old Naval Observatory is now on the grounds of the United States Navy Bureau of Medicine and Surgery, southwest of the corner of E and 23rd Streets in Foggy Bottom (north of the Lincoln Memorial). Washington mean time was sometimes called Washington meridian time. It was never used as the basis of any time zone, although it was the local mean time of the city of Washington before the advent of American time zones on 18 November 1883. It was also used to time astronomical events by users of the American Ephemeris and Nautical Almanac, first published for the year 1855.
The difference between Washington mean time and Greenwich Mean Time was determined to be 5 hours 8 minutes 12.04 seconds in 1884 by the U.S. Coast and Geodetic Survey. This is equivalent to 77°3'0.6"W. However, most sources cite 77°3'2.3"W as the Washington meridian to which the borders of several western states are referred. The difference may be due to polar motion which was not yet recognized in 1884. This old Washington meridian was repealed on 22 August 1912 (37 Stat. 342). Nevertheless, Washington mean time was still being used in 1950 on a few pages of the American Ephemeris and Nautical Almanac, even though most of its pages used Greenwich Civil Time, the American name for the midnight epoch Greenwich Mean Time. For astronomical purposes, before 1925 a day was considered to start at noon rather than the previous midnight. Thus to convert times of astronomical events before 1925 given in Washington mean time to modern Universal Time it is necessary to add not 05:08:12.04 but 17:08:12.04.
In the United Kingdom, continental time refers to a time-keeping system used on the mainland of Europe, either the 24-hour clock, or the Central European Time zone. The former usage has become rarer as the UK uses the 24-hour clock more.
A synodic day is the period of time it takes for a planet to rotate once in relation to the body it is orbiting (as opposed to a sidereal day which is one complete rotation in relation to the stars).
Thus, a synodic day may be 'sunrise to sunrise', whereas a sidereal day may be 'star-rise to star-rise'. These two quantities are not equal because the Sun, as seen from Earth, moves against the fixed sphere of stars along an imaginary line known as the ecliptic. The Sun appears to move a little less than a degree each day, (360 degrees/year)/(365.25 days/year), toward the east in a manner known as prograde motion.
Although correct, neither term can be defined as the rising or setting of a celestial body because of variations due to the Earth's tilt. See the equation of time.
For Earth, the synodic day is known as a solar day, and is 24 hours long.
The Eastern Time Zone (ET) of the Western Hemisphere falls mostly along the east coast of North America and the west coast of South America. Its time offset is -5 hrs GMT or UTC-5 during standard time and UTC-4 during daylight saving time. The clock time in this zone is based on the mean solar time of the 75th meridian west of the Greenwich Observatory.
In the United States and Canada, this time zone is generally called Eastern Time (ET). Specifically, it is Eastern Standard Time (EST) when observing standard time (winter), and Eastern Daylight Time (EDT) when observing daylight saving time (summer). The 1966 Uniform Time Act in the USA meant that EDT was instituted on the last Sunday in April, starting in 1966, throughout most of the USA.<ref name = "edt"> </ref> EST would be re-instituted on the last Sunday in October. The act was amended to make the first Sunday in April the beginning of EDT as of 1987.<ref name = "edt"/> The Energy Policy Act of 2005 extended daylight saving time in the U.S. beginning in 2007. The local time changes at 02:00 EST to 03:00 EDT on the second Sunday in March and returns at 02:00 EDT to 01:00 EST on the first Sunday in November<ref name = "edt"/>. In Canada, the time changes as it does in the U.S.
The term ephemeris time is in itself apt to refer to time in connection with any astronomical ephemeris. It has been used more specifically to refer:-
(1) to a (former standard) astronomical time scale, officially ephemeris time, sometimes designated ET. This was adopted in 1952 by IAU,<ref name=ESAE>'ESAE 1961': 'Explanatory Supplement to the Astronomical Ephemeris and the American Ephemeris and Nautical Almanac' ('prepared jointly by the Nautical Almanac Offices of the United Kingdom and the United States of America', HMSO, London, 1961), esp. p.9</ref> and superseded in the 1970s.<ref name=ESAA>'ESAA (1992)': (ed) P K Seidelmann, 'Explanatory Supplement to the Astronomical Almanac', University Science Books, CA, 1992 ; ISBN 0-935702-68-7, esp. at pp.41-42.</ref> This time scale was proposed in 1948, to overcome the drawbacks of irregularly fluctuating mean solar time. The intent was to define a uniform time (as far as was then feasible) based on Newtonian theory (see Definition of ephemeris time (1952)).
also
(2) (sometimes in past, but with risk of confusion with (1)) to a modern relativistic coordinate time scale, implemented by the JPL ephemeris time argument T<sub>eph</sub>, in a series of numerically integrated Development Ephemerides. Among them is the DE405 ephemeris in widespread current use. The time scale represented by T<sub>eph</sub> is closely related to, but distinct (by an offset and constant rate) from, the TCB time scale currently adopted as a standard by the IAU (see JPL ephemeris time argument Teph).<ref name=EMS1998>E M Standish, 'Time scales in the JPL and CfA ephemerides', Astron & Astrophys 336 (1998), 381-384.</ref>
Most of the following sections relate to the ephemeris time of the 1952 standard.
An impression has sometimes arisen that ephemeris time was in use from 1900: this probably arose because ET, though proposed and adopted in the period 1948-1952, was defined in detail using formulae that made retrospective use of the epoch date of 1900 Jan 0 and of Newcomb's Tables of the Sun.See ESAE (1961), e.g. pp.69 and 87, and Clemence (1948), at p.172
The ephemeris time of the 1952 standard leaves a continuing legacy, through its ephemeris second which became closely duplicated in the length of the current standard SI second (see Redefinition of the second).
