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Wikipedia

Time zone

January 01, 1970

This article is about time zones in general. For a list of time zones by country, see List of time zones by country. For more time zone lists, see Lists of time zones. For other uses, see Time zone (disambiguation).

A time zone is an area which observes a uniform standard time for legal, commercial and social purposes. Time zones tend to follow the boundaries between countries and their subdivisions instead of strictly following longitude, because it is convenient for areas in frequent communication to keep the same time.

Time zones of the world

Each time zone is defined by a standard offset from Coordinated Universal Time (UTC). The offsets range from UTC−12:00 to UTC+14:00, and are usually a whole number of hours, but a few zones are offset by an additional 30 or 45 minutes, such as in India and Nepal. Some areas in a time zone may use a different offset for part of the year, typically one hour ahead during spring and summer, a practice known as daylight saving time (DST).

List of UTC offsets

Main article: List of UTC time offsets
 
Time zones of the world

In the table below, the locations that use daylight saving time (DST) are listed in their UTC offset when DST is not in effect. When DST is in effect, approximately during spring and summer, their UTC offset is increased by one hour (except for Lord Howe Island, where it is increased by 30 minutes). For example, during the DST period California observes UTC−07:00 and the United Kingdom observes UTC+01:00.

UTC offset Locations that do not use DST Locations that use DST
UTC−12:00
UTC−11:00
UTC−10:00
  Cook Islands
  French Polynesia (most)
  Johnston Atoll
  United States: Hawaii
   United States: Andreanof Islands, Islands of Four Mountains, Near Islands, Rat Islands (Aleutian Islands, Alaska)
UTC−09:30   French Polynesia: Marquesas Islands
UTC−09:00   French Polynesia: Gambier Islands   United States: Alaska (most)
UTC−08:00   Clipperton Island
  Pitcairn Islands
UTC−07:00   Canada: British Columbia (northeast), Yukon
  Mexico: Baja California Sur, Nayarit (most), Sinaloa, Sonora
  United States: Arizona (most) 		  Canada: Alberta, British Columbia (southeast), Northwest Territories, Nunavut (west)
  Mexico: Chihuahua (northwest border)
  United States: Arizona (Navajo Nation), Colorado, Idaho (most), Kansas (west), Montana, Nebraska (west), New Mexico, Nevada (northeast border), North Dakota (southwest), Oregon (east), South Dakota (west), Texas (west), Utah, Wyoming
UTC−06:00
  Canada: Manitoba, Nunavut (central), Ontario (west)
  Chile: Easter Island
  Mexico (northeast border)
  United States: Alabama, Arkansas, Florida (northwest), Illinois, Indiana (northwest, southwest), Iowa, Kansas (most), Kentucky (west), Louisiana, Michigan (northwest border), Minnesota, Mississippi, Missouri, Nebraska (most), North Dakota (most), Oklahoma, South Dakota (most), Tennessee (most), Texas (most), Wisconsin
UTC−05:00
UTC−04:00   Bermuda
  Canada: Labrador (most), New Brunswick, Nova Scotia, Prince Edward Island
  Chile (most)
  Greenland: Pituffik Space Base
  Paraguay
UTC−03:30   Canada: Newfoundland, Labrador (southeast)
UTC−03:00   Saint Pierre and Miquelon
UTC−02:00   Brazil: Fernando de Noronha
  South Georgia and the South Sandwich Islands 		  Greenland (most)
UTC−01:00   Cape Verde   Portugal: Azores
UTC+00:00   Faroe Islands
  Guernsey
  Ireland
  Isle of Man
  Jersey
  Portugal (most)
  Spain: Canary Islands
  United Kingdom
UTC+01:00
UTC+02:00
UTC+03:00
UTC+03:30   Iran
UTC+04:00
UTC+04:30   Afghanistan
UTC+05:00
UTC+05:30
UTC+05:45   Nepal
UTC+06:00
UTC+06:30
UTC+07:00
UTC+08:00
UTC+08:45   Australia: Eucla
UTC+09:00
UTC+09:30   Australia: Northern Territory   Australia: South Australia, Yancowinna County[5]
UTC+10:00   Australia: Australian Capital Territory, Jervis Bay Territory, New South Wales (most), Tasmania, Victoria
UTC+10:30   Australia: Lord Howe Island (DST increase is 30 minutes)
UTC+11:00   Norfolk Island
UTC+12:00   New Zealand (most)
UTC+12:45   New Zealand: Chatham Islands
UTC+13:00
UTC+14:00   Kiribati: Line Islands

History

The apparent position of the Sun in the sky, and thus solar time, varies by location due to the spherical shape of the Earth. This variation corresponds to four minutes of time for every degree of longitude, so for example when it is solar noon in London, it is about 10 minutes before solar noon in Bristol, which is about 2.5 degrees to the west.[6]

The Royal Observatory, Greenwich, founded in 1675, established Greenwich Mean Time (GMT), the mean solar time at that location, as an aid to mariners to determine longitude at sea, providing a standard reference time while each location in England kept a different time.

Railway time

Main article: Railway time
 
Plaque commemorating the Railway General Time Convention of 1883 in North America
 
The control panel of the Time Zone Clock in front of Coventry Transport Museum

In the 19th century, as transportation and telecommunications improved, it became increasingly inconvenient for each location to observe its own solar time. In November 1840, the British Great Western Railway started using GMT kept by portable chronometers.[7][failed verification] This practice was soon followed by other railway companies in Great Britain and became known as Railway Time.

Around August 23, 1852, time signals were first transmitted by telegraph from the Royal Observatory. By 1855, 98% of Great Britain's public clocks were using GMT, but it was not made the island's legal time until August 2, 1880. Some British clocks from this period have two minute hands, one for the local time and one for GMT.[8]

On November 2, 1868, the then British Colony of New Zealand officially adopted a standard time to be observed throughout the colony.[9] It was based on longitude 172°30′ east of Greenwich, that is 11 hours 30 minutes ahead of GMT. This standard was known as New Zealand Mean Time.[10]

 
1913 time zone map of the United States, showing boundaries very different from today

Timekeeping on North American railroads in the 19th century was complex. Each railroad used its own standard time, usually based on the local time of its headquarters or most important terminus, and the railroad's train schedules were published using its own time. Some junctions served by several railroads had a clock for each railroad, each showing a different time.[11]

Around 1863, Charles F. Dowd proposed a system of hourly standard time zones for North American railroads, although he published nothing on the matter at that time and did not consult railroad officials until 1869. In 1870 he proposed four ideal time zones having north–south borders, the first centered on Washington, D.C., but by 1872 the first was centered on meridian 75° west of Greenwich, with natural borders such as sections of the Appalachian Mountains. Dowd's system was never accepted by North American railroads. Chief meteorologist at the United States Weather Bureau Cleveland Abbe divided the United States into four standard time zones for consistency among the weather stations. In 1879, he published a paper titled Report on Standard Time.[12] In 1883, he convinced North American railroad companies to adopt his time-zone system. In 1884, Britain, which had already adopted its own standard time system for England, Scotland, and Wales, helped gather international consent for global time. In time, the American government, influenced in part by Abbe's 1879 paper, adopted the time-zone system.[13] It was a version proposed by William F. Allen, the editor of the Traveler's Official Railway Guide.[14] The borders of its time zones ran through railroad stations, often in major cities. For example, the border between its Eastern and Central time zones ran through Detroit, Buffalo, Pittsburgh, Atlanta, and Charleston. It was inaugurated on Sunday, November 18, 1883, also called "The Day of Two Noons",[15] when each railroad station clock was reset as standard-time noon was reached within each time zone.

The North American zones were named Intercolonial, Eastern, Central, Mountain, and Pacific. Within a year 85% of all cities with populations over 10,000 (about 200 cities) were using standard time.[16] A notable exception was Detroit (located about halfway between the meridians of Eastern and Central time), which kept local time until 1900, then tried Central Standard Time, local mean time, and Eastern Standard Time (EST) before a May 1915 ordinance settled on EST and was ratified by popular vote in August 1916. The confusion of times came to an end when standard time zones were formally adopted by the U.S. Congress in the Standard Time Act of March 19, 1918.

Worldwide time zones

"World time" redirects here. For the global time standard, see Universal Time.

Italian mathematician Quirico Filopanti introduced the idea of a worldwide system of time zones in his book Miranda!, published in 1858. He proposed 24 hourly time zones, which he called "longitudinal days", the first centred on the meridian of Rome. He also proposed a universal time to be used in astronomy and telegraphy. However, his book attracted no attention until long after his death.[17][18]

Scottish-born Canadian Sir Sandford Fleming proposed a worldwide system of time zones in 1876 - see Sandford Fleming § Inventor of worldwide standard time. The proposal divided the world into twenty-four time zones labeled A-Y (skipping J), each one covering 15 degrees of longitude. All clocks within each zone would be set to the same time as the others, but differed by one hour from those in the neighboring zones.[19] He advocated his system at several international conferences, including the International Meridian Conference, where it received some consideration. The system has not been directly adopted, but some maps divide the world into 24 time zones and assign letters to them, similarly to Fleming's system.[20]

 
World map of time zones in 1928

By about 1900, almost all inhabited places on Earth had adopted a standard time zone, but only some of them used an hourly offset from GMT. Many applied the time at a local astronomical observatory to an entire country, without any reference to GMT. It took many decades before all time zones were based on some standard offset from GMT or Coordinated Universal Time (UTC). By 1929, the majority of countries had adopted hourly time zones, though some countries such as Iran, India, Myanmar and parts of Australia had time zones with a 30-minute offset. Nepal was the last country to adopt a standard offset, shifting slightly to UTC+05:45 in 1986.[21]

All nations currently use standard time zones for secular purposes, but not all of them apply the concept as originally conceived. Several countries and subdivisions use half-hour or quarter-hour deviations from standard time. Some countries, such as China and India, use a single time zone even though the extent of their territory far exceeds the ideal 15° of longitude for one hour; other countries, such as Spain and Argentina, use standard hour-based offsets, but not necessarily those that would be determined by their geographical location. The consequences, in some areas, can affect the lives of local citizens, and in extreme cases contribute to larger political issues, such as in the western reaches of China.[22] In Russia, which has 11 time zones, two time zones were removed in 2010[23][24] and reinstated in 2014.[25]

Notation

ISO 8601

Main article: ISO 8601

ISO 8601 is a standard established by the International Organization for Standardization defining methods of representing dates and times in textual form, including specifications for representing time zones.

If a time is in Coordinated Universal Time (UTC), a "Z" is added directly after the time without a separating space. "Z" is the zone designator for the zero UTC offset. "09:30 UTC" is therefore represented as "09:30Z" or "0930Z". Likewise, "14:45:15 UTC" is written as "14:45:15Z" or "144515Z".[26] UTC time is also known as "Zulu" time, since "Zulu" is a phonetic alphabet code word for the letter "Z".[26]

Offsets from UTC are written in the format ±hh:mm, ±hhmm, or ±hh (either hours ahead or behind UTC). For example, if the time being described is one hour ahead of UTC (such as the time in Germany during the winter), the zone designator would be "+01:00", "+0100", or simply "+01". This numeric representation of time zones is appended to local times in the same way that alphabetic time zone abbreviations (or "Z", as above) are appended. The offset from UTC changes with daylight saving time, e.g. a time offset in Chicago, which is in the North American Central Time Zone, is "−06:00" for the winter (Central Standard Time) and "−05:00" for the summer (Central Daylight Time).[27]

Abbreviations

Main article: List of time zone abbreviations

Time zones are often represented by alphabetic abbreviations such as "EST", "WST", and "CST", but these are not part of the international time and date standard ISO 8601. Such designations can be ambiguous; for example, "CST" can mean (North American) Central Standard Time (UTC−06:00), Cuba Standard Time (UTC−05:00) and China Standard Time (UTC+08:00), and it is also a widely used variant of ACST (Australian Central Standard Time, UTC+09:30).[28]

Conversions

Conversion between time zones obeys the relationship

"time in zone A" − "UTC offset for zone A" = "time in zone B" − "UTC offset for zone B",

in which each side of the equation is equivalent to UTC.

The conversion equation can be rearranged to

"time in zone B" = "time in zone A" − "UTC offset for zone A" + "UTC offset for zone B".

For example, the New York Stock Exchange opens at 09:30 (EST, UTC offset= −05:00). In California (PST, UTC offset= −08:00) and India (IST, UTC offset= +05:30), the New York Stock Exchange opens at

time in California = 09:30 − (−05:00) + (−08:00) = 06:30;
time in India = 09:30 − (−05:00) + (+05:30) = 20:00.

These calculations become more complicated near the time switch to or from daylight saving time, as the UTC offset for the area becomes a function of UTC time.

The time differences may also result in different dates. For example, when it is 22:00 on Monday in Egypt (UTC+02:00), it is 01:00 on Tuesday in Pakistan (UTC+05:00).

The table "Time of day by zone" gives an overview on the time relations between different zones.

Nautical time zones

Main article: Nautical time

Since the 1920s, a nautical standard time system has been in operation for ships on the high seas. As an ideal form of the terrestrial time zone system, nautical time zones consist of gores of 15° offset from GMT by a whole number of hours. A nautical date line follows the 180th meridian, bisecting one 15° gore into two 7.5° gores that differ from GMT by ±12 hours.[29][30][31]

However, in practice each ship may choose what time to observe at each location. Ships may decide to adjust their clocks at a convenient time, usually at night, not exactly when they cross a certain longitude.[32] Some ships simply remain on the time of the departing port during the whole trip.[33]

Skewing of time zones

 
Difference between sun time and clock time during daylight saving time:
1h ± 30 min behind
0h ± 30m
1h ± 30 m ahead
2h ± 30 m ahead
3h ± 30 m ahead
 
  DST observed
  DST formerly observed
  DST never observed

Ideal time zones, such as nautical time zones, are based on the mean solar time of a particular meridian in the middle of that zone with boundaries located 7.5 degrees east and west of the meridian. In practice, however, many time zone boundaries are drawn much farther to the west, and some countries are located entirely outside their ideal time zones.

For example, even though the Prime Meridian (0°) passes through Spain and France, they use the mean solar time of 15 degrees east (Central European Time) rather than 0 degrees (Greenwich Mean Time). France previously used GMT, but was switched to CET (Central European Time) during the German occupation of the country during World War II and did not switch back after the war.[34] Similarly, prior to World War II, the Netherlands observed "Amsterdam Time", which was twenty minutes ahead of Greenwich Mean Time. They were obliged to follow German time during the war, and kept it thereafter. In the mid-1970s the Netherlands, as other European states, began observing daylight saving (summer) time.

One reason to draw time zone boundaries far to the west of their ideal meridians is to allow the more efficient use of afternoon sunlight.[35] Some of these locations also use daylight saving time (DST), further increasing the difference to local solar time. As a result, in summer, solar noon in the Spanish city of Vigo occurs at 14:41 clock time. This westernmost area of continental Spain never experiences sunset before 18:00 clock time, even in winter, despite lying 42 degrees north of the equator.[36] Near the summer solstice, Vigo has sunset times after 22:00, similar to those of Stockholm, which is in the same time zone and 17 degrees farther north. Stockholm has much earlier sunrises, though.[37]

A more extreme example is Nome, Alaska, which is at 165°24′W longitude – just west of center of the idealized Samoa Time Zone (165°W). Nevertheless, Nome observes Alaska Time (135°W) with DST so it is slightly more than two hours ahead of the sun in winter and over three in summer.[38] Kotzebue, Alaska, also near the same meridian but north of the Arctic Circle, has two sunsets on the same day in early August, one shortly after midnight at the start of the day, and the other shortly before midnight at the end of the day.[39]

China extends as far west as 73°E, but all parts of it use UTC+08:00 (120°E), so solar "noon" can occur as late as 15:00 in western portions of China such as Xinjiang.[40] The Afghanistan-China border marks the greatest terrestrial time zone difference on Earth, with a 3.5 hour difference between Afghanistan's UTC+4:30 and China's UTC+08:00.

 
A visualization of the mismatch between clock time and solar time in different locations. In blue areas, clock time lags behind solar time; in red areas, the reverse is true. The two are synchronized in the white areas.

Daylight saving time

Main article: Daylight saving time

Many countries, and sometimes just certain regions of countries, adopt daylight saving time (DST), also known as summer time, during part of the year. This typically involves advancing clocks by an hour near the start of spring and adjusting back in autumn ("spring forward", "fall back"). Modern DST was first proposed in 1907 and was in widespread use in 1916 as a wartime measure aimed at conserving coal. Despite controversy, many countries have used it off and on since then; details vary by location and change occasionally. Countries around the equator usually do not observe daylight saving time, since the seasonal difference in sunlight there is minimal.

Computer systems

Many computer operating systems include the necessary support for working with all (or almost all) possible local times based on the various time zones. Internally, operating systems typically use UTC as their basic time-keeping standard, while providing services for converting local times to and from UTC, and also the ability to automatically change local time conversions at the start and end of daylight saving time in the various time zones. (See the article on daylight saving time for more details on this aspect.)

Web servers presenting web pages primarily for an audience in a single time zone or a limited range of time zones typically show times as a local time, perhaps with UTC time in brackets. More internationally oriented websites may show times in UTC only or using an arbitrary time zone. For example, the international English-language version of CNN includes GMT and Hong Kong Time,[41] whereas the US version shows Eastern Time.[42] US Eastern Time and Pacific Time are also used fairly commonly on many US-based English-language websites with global readership. The format is typically based in the W3C Note "datetime".

Email systems and other messaging systems (IRC chat, etc.)[43] time-stamp messages using UTC, or else include the sender's time zone as part of the message, allowing the receiving program to display the message's date and time of sending in the recipient's local time.

Database records that include a time stamp typically use UTC, especially when the database is part of a system that spans multiple time zones. The use of local time for time-stamping records is not recommended for time zones that implement daylight saving time because once a year there is a one-hour period when local times are ambiguous.

Calendar systems nowadays usually tie their time stamps to UTC, and show them differently on computers that are in different time zones. That works when having telephone or internet meetings. It works less well when travelling, because the calendar events are assumed to take place in the time zone the computer or smartphone was on when creating the event. The event can be shown at the wrong time. For example, if a New Yorker plans to meet someone in Los Angeles at 9 am, and makes a calendar entry at 9 am (which the computer assumes is New York time), the calendar entry will be at 6 am if taking the computer's time zone. There is also an option in newer versions of Microsoft Outlook to enter the time zone in which an event will happen, but often not in other calendar systems. Calendaring software must also deal with daylight saving time (DST). If, for political reasons, the begin and end dates of daylight saving time are changed, calendar entries should stay the same in local time, even though they may shift in UTC time. In Microsoft Outlook, time stamps are therefore stored and communicated without DST offsets.[44] Hence, an appointment in London at noon in the summer will be represented as 12:00 (UTC+00:00) even though the event will actually take place at 13:00 UTC. In Google Calendar, calendar events are stored in UTC (although shown in local time) and might be changed by a time-zone changes,[45] although normal daylight saving start and end are compensated for (similar to much other calendar software).

Operating systems

Unix

Main article: Unix time

Unix-like systems, including Linux and macOS, keep system time in Unix time format, representing the number of seconds (excluding leap seconds) that have elapsed since 00:00:00 Coordinated Universal Time (UTC) on Thursday, January 1, 1970.[46] Unix time is usually converted to local time when displayed to the user, and times specified by the user in local time are converted to Unix time. The conversion takes into account the time zone and daylight saving time rules; by default the time zone and daylight saving time rules are set up when the system is configured, though individual processes can specify time zones and daylight saving time rules using the TZ environment variable.[47] This allows users in multiple time zones, or in the same time zone but with different daylight saving time rules, to use the same computer, with their respective local times displayed correctly to each user. Time zone and daylight saving time rule information most commonly comes from the IANA time zone database. In fact, many systems, including anything using the GNU C Library, a C library based on the BSD C library, or the System V Release 4 C library, can make use of this database.

Microsoft Windows

Windows-based computer systems prior to Windows 95 and Windows NT used local time, but Windows 95 and later, and Windows NT, base system time on UTC.[48][49] They allow a program to fetch the system time as UTC, represented as a year, month, day, hour, minute, second, and millisecond;[50][51] Windows 95 and later, and Windows NT 3.5 and later, also allow the system time to be fetched as a count of 100 ns units since 1601-01-01 00:00:00 UTC.[52][53] The system registry contains time zone information that includes the offset from UTC and rules that indicate the start and end dates for daylight saving in each zone. Interaction with the user normally uses local time, and application software is able to calculate the time in various zones. Terminal Servers allow remote computers to redirect their time zone settings to the Terminal Server so that users see the correct time for their time zone in their desktop/application sessions. Terminal Services uses the server base time on the Terminal Server and the client time zone information to calculate the time in the session.

Programming languages

Java

While most application software will use the underlying operating system for time zone and daylight saving time rule information, the Java Platform, from version 1.3.1, has maintained its own database of time zone and daylight saving time rule information. This database is updated whenever time zone or daylight saving time rules change. Oracle provides an updater tool for this purpose.[54]

As an alternative to the information bundled with the Java Platform, programmers may choose to use the Joda-Time library.[55] This library includes its own data based on the IANA time zone database.[56]

As of Java 8 there is a new date and time API that can help with converting times.[57]

JavaScript

Traditionally, there was very little in the way of time zone support for JavaScript. Essentially the programmer had to extract the UTC offset by instantiating a time object, getting a GMT time from it, and differencing the two. This does not provide a solution for more complex daylight saving variations, such as divergent DST directions between northern and southern hemispheres.

ECMA-402, the standard on Internationalization API for JavaScript, provides ways of formatting Time Zones.[58] However, due to size constraint, some implementations or distributions do not include it.[59]

Perl

The DateTime object in Perl supports all entries in the IANA time zone database and includes the ability to get, set and convert between time zones.[60]

PHP

The DateTime objects and related functions have been compiled into the PHP core since 5.2. This includes the ability to get and set the default script time zone, and DateTime is aware of its own time zone internally. PHP.net provides extensive documentation on this.[61] As noted there, the most current time zone database can be implemented via the PECL timezonedb.

Python

The standard module datetime included with Python stores and operates on the time zone information class tzinfo. The third party pytz module provides access to the full IANA time zone database.[62] Negated time zone offset in seconds is stored time.timezone and time.altzone attributes. From Python 3.9, the zoneinfo module introduces timezone management without need for third party module.[63]

Smalltalk

Each Smalltalk dialect comes with its own built-in classes for dates, times and timestamps, only a few of which implement the DateAndTime and Duration classes as specified by the ANSI Smalltalk Standard. VisualWorks provides a TimeZone class that supports up to two annually recurring offset transitions, which are assumed to apply to all years (same behavior as Windows time zones). Squeak provides a Timezone class that does not support any offset transitions. Dolphin Smalltalk does not support time zones at all.

For full support of the tz database (zoneinfo) in a Smalltalk application (including support for any number of annually recurring offset transitions, and support for different intra-year offset transition rules in different years) the third-party, open-source, ANSI-Smalltalk-compliant Chronos Date/Time Library is available for use with any of the following Smalltalk dialects: VisualWorks, Squeak, Gemstone, or Dolphin.[64]

Time in outer space

Orbiting spacecraft may experience many sunrises and sunsets, or none, in a 24-hour period. Therefore, it is not possible to calibrate the time with respect to the Sun and still respect a 24-hour sleep/wake cycle. A common practice for space exploration is to use the Earth-based time of the launch site or mission control, synchronizing the sleeping cycles of the crew and controllers. The International Space Station normally uses Greenwich Mean Time (GMT).[65][66]

Timekeeping on Mars can be more complex, since the planet has a solar day of approximately 24 hours and 40 minutes, known as a sol. Earth controllers for some Mars missions have synchronized their sleep/wake cycles with the Martian day, because solar-powered rover activity on the surface was tied to periods of light and dark.[67]

See also

Notes

  1. ^ a b Observes UTC+00:00 around Ramadan.[1][2][3]

References

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  2. ^ "Time Zone in Casablanca, Morocco". Timeanddate.com. from the original on March 30, 2021.
  3. ^ "Time Zone in El Aaiún, Western Sahara". Timeanddate.com. from the original on February 14, 2021.
  4. ^ a b "Décret nº 2017-292 du 6 mars 2017 relatif au temps légal français" [Decree no. 2017-292 of 6 March 2017 relative to French legal time] (in French). Légifrance. March 8, 2017. from the original on December 2, 2020.
  5. ^ "Standard Time Act 1987 No 149". New South Wales Government. Retrieved February 29, 2024.
  6. ^ "Latitude and Longitude of World Cities". Infoplease. from the original on May 24, 2011. Retrieved April 18, 2012.
  7. ^ "WESTMINSTER MEDICAL SOCIETY. Saturday, November 21, 1840". The Lancet. 35 (901): 383. December 1840. doi:10.1016/s0140-6736(00)59842-0. ISSN 0140-6736. from the original on March 30, 2021. Retrieved January 27, 2021.
  8. ^ . GreenwichMeanTime.com. Archived from the original on June 28, 2006. Retrieved December 5, 2011.
  9. ^ "Telegraph line laid across Cook Strait". New Zealand Ministry for Culture and Heritage. from the original on February 18, 2020. Retrieved January 5, 2020.
  10. ^ "Our Time. How we got it. New Zealand's Method. A Lead to the World". Papers Past. Evening Post. p. 10. from the original on October 8, 2013. Retrieved October 2, 2013.
  11. ^ Alfred, Randy (November 18, 2010). "Nov. 18, 1883: Railroad Time Goes Coast to Coast". Wired. from the original on August 19, 2018. Retrieved July 30, 2018.
  12. ^ Debus 1968, p. 2
  13. ^ Asimov 1964, p. 344
  14. ^ (PDF). Archived from the original (PDF) on May 14, 2012.  (1.89 MB)
  15. ^ "The Times Reports on "the Day of Two Noons"". History Matters. from the original on April 4, 2012. Retrieved December 5, 2011.
  16. ^ . Sos.state.il.us. Archived from the original on October 5, 2011. Retrieved December 5, 2011.
  17. ^ Quirico Filopanti from scienzagiovane, Bologna University, Italy. January 17, 2013, at the Wayback Machine
  18. ^ Gianluigi Parmeggiani (Osservatorio Astronomico di Bologna), The origin of time zones August 24, 2007, at the Wayback Machine
  19. ^ Fleming, Sandford (1886). "Time-reckoning for the twentieth century". Annual Report of the Board of Regents of the Smithsonian Institution (1): 345–366. from the original on October 5, 2022. Retrieved March 24, 2022. Reprinted in 1889: Time-reckoning for the twentieth century at the Internet Archive.
  20. ^ Stromberg, Joseph (November 18, 2011). "Sandford Fleming Sets the World's Clock". Smithsonian Magazine. from the original on March 24, 2022. Retrieved March 24, 2022.
  21. ^ "Time Zone & Clock Changes in Kathmandu, Nepal". timeanddate.com. from the original on January 22, 2021. Retrieved December 1, 2020.
  22. ^ Schiavenza, Matt (November 5, 2013). "China Only Has One Time Zone—and That's a Problem". The Atlantic. from the original on August 22, 2018. Retrieved August 22, 2018.
  23. ^ "Russia Reduces Number of Time Zones". TimeAndDate.com. March 23, 2010. from the original on August 9, 2020. Retrieved May 31, 2020.
  24. ^ "About Time: Huge country, nine time zones" (Video). BBC. March 22, 2011. from the original on February 13, 2019. Retrieved February 12, 2019.
  25. ^ "Russian clocks to retreat again in winter, 11 time zones return". Reuters. July 2014. from the original on October 28, 2020. Retrieved October 25, 2020.
  26. ^ a b "Z – Zulu Time Zone (Time Zone Abbreviation)". TimeAndDate.com. from the original on August 22, 2018. Retrieved August 22, 2018.
  27. ^ "What is UTC or GMT Time?". National Hurricane Center. from the original on August 22, 2018. Retrieved August 22, 2018.
  28. ^ "Time Zone Abbreviations – Worldwide List", Timeanddate.com. August 21, 2018, at the Wayback Machine.
  29. ^ Bowditch, Nathaniel. American Practical Navigator. Washington: Government Printing Office, 1925, 1939, 1975.
  30. ^ Hill, John C., Thomas F. Utegaard, Gerard Riordan. Dutton's Navigation and Piloting. Annapolis: United States Naval Institute, 1958.
  31. ^ Howse, Derek. Greenwich Time and the Discovery of the Longitude. Oxford: Oxford University Press, 1980. ISBN 0-19-215948-8.
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Sources

  • Asimov, Isaac (1964). "Abbe, Cleveland". Asimov's Biographical Encyclopedia of Science and Technology: The Living Stories of More than 1000 Great Scientists from the Age of Greece to the Space Age. Garden City, NY: Doubleday & Company, Inc. pp. 343–344. LCCN 64016199.
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Further reading

  • Biswas, Soutik (February 12, 2019). "How India's single time zone is hurting its people". BBC News. Retrieved February 12, 2019.
  • Maulik Jagnani, economist at Cornell University (January 15, 2019). "PoorSleep: Sunset Time and Human Capital Production" (Job Market Paper). Retrieved February 12, 2019.
  • "Time Bandits: The countries rebelling against GMT" (Video). BBC News. August 14, 2015. Retrieved February 12, 2019.
  • "How time zones confused the world". BBC News. August 7, 2015. Retrieved February 12, 2019.
  • Lane, Megan (May 10, 2011). "How does a country change its time zone?". BBC News. Retrieved February 12, 2019.
  • "A brief history of time zones" (Video). BBC News. March 24, 2011. Retrieved February 12, 2019.
  • The Time Zone Information Format (TZif). doi:10.17487/RFC8536. RFC 8536.

External links

 
Wikivoyage has a travel guide for Time zones.
  •   Media related to Time zones at Wikimedia Commons

January 01, 1970
time, zone, this, article, about, time, zones, general, list, time, zones, country, list, time, zones, country, more, time, zone, lists, lists, time, zones, other, uses, disambiguation, time, zone, area, which, observes, uniform, standard, time, legal, commerc. This article is about time zones in general For a list of time zones by country see List of time zones by country For more time zone lists see Lists of time zones For other uses see Time zone disambiguation A time zone is an area which observes a uniform standard time for legal commercial and social purposes Time zones tend to follow the boundaries between countries and their subdivisions instead of strictly following longitude because it is convenient for areas in frequent communication to keep the same time Time zones of the world Each time zone is defined by a standard offset from Coordinated Universal Time UTC The offsets range from UTC 12 00 to UTC 14 00 and are usually a whole number of hours but a few zones are offset by an additional 30 or 45 minutes such as in India and Nepal Some areas in a time zone may use a different offset for part of the year typically one hour ahead during spring and summer a practice known as daylight saving time DST Contents 1 List of UTC offsets 2 History 2 1 Railway time 2 2 Worldwide time zones 3 Notation 3 1 ISO 8601 3 2 Abbreviations 4 Conversions 5 Nautical time zones 6 Skewing of time zones 7 Daylight saving time 8 Computer systems 8 1 Operating systems 8 1 1 Unix 8 1 2 Microsoft Windows 8 2 Programming languages 8 2 1 Java 8 2 2 JavaScript 8 2 3 Perl 8 2 4 PHP 8 2 5 Python 8 2 6 Smalltalk 9 Time in outer space 10 See also 11 Notes 12 References 13 Sources 14 Further reading 15 External linksList of UTC offsetsMain article List of UTC time offsets nbsp Time zones of the world In the table below the locations that use daylight saving time DST are listed in their UTC offset when DST is not in effect When DST is in effect approximately during spring and summer their UTC offset is increased by one hour except for Lord Howe Island where it is increased by 30 minutes For example during the DST period California observes UTC 07 00 and the United Kingdom observes UTC 01 00 UTC offset Locations that do not use DST Locations that use DST UTC 12 00 nbsp Baker Island nbsp Howland Island UTC 11 00 nbsp American Samoa nbsp Jarvis Island nbsp Kingman Reef nbsp Midway Atoll nbsp Niue nbsp Palmyra Atoll UTC 10 00 nbsp Cook Islands nbsp French Polynesia most nbsp Johnston Atoll nbsp United States Hawaii nbsp United States Andreanof Islands Islands of Four Mountains Near Islands Rat Islands Aleutian Islands Alaska UTC 09 30 nbsp French Polynesia Marquesas Islands UTC 09 00 nbsp French Polynesia Gambier Islands nbsp United States Alaska most UTC 08 00 nbsp Clipperton Island nbsp Pitcairn Islands nbsp Canada British Columbia most nbsp Mexico Baja California nbsp United States California Idaho north Nevada most Oregon most Washington UTC 07 00 nbsp Canada British Columbia northeast Yukon nbsp Mexico Baja California Sur Nayarit most Sinaloa Sonora nbsp United States Arizona most nbsp Canada Alberta British Columbia southeast Northwest Territories Nunavut west nbsp Mexico Chihuahua northwest border nbsp United States Arizona Navajo Nation Colorado Idaho most Kansas west Montana Nebraska west New Mexico Nevada northeast border North Dakota southwest Oregon east South Dakota west Texas west Utah Wyoming UTC 06 00 nbsp Belize nbsp Canada Saskatchewan most nbsp Costa Rica nbsp Ecuador Galapagos nbsp El Salvador nbsp Guatemala nbsp Honduras nbsp Mexico most nbsp Nicaragua nbsp Canada Manitoba Nunavut central Ontario west nbsp Chile Easter Island nbsp Mexico northeast border nbsp United States Alabama Arkansas Florida northwest Illinois Indiana northwest southwest Iowa Kansas most Kentucky west Louisiana Michigan northwest border Minnesota Mississippi Missouri Nebraska most North Dakota most Oklahoma South Dakota most Tennessee most Texas most Wisconsin UTC 05 00 nbsp Brazil Acre Amazonas southwest nbsp Canada Atikokan Mishkeegogamang Southampton Island nbsp Cayman Islands nbsp Colombia nbsp Ecuador most nbsp Jamaica nbsp Mexico Quintana Roo nbsp Navassa Island nbsp Panama nbsp Peru nbsp Bahamas nbsp Canada Nunavut east Ontario most Quebec most nbsp Cuba nbsp Haiti nbsp Turks and Caicos Islands nbsp United States Connecticut Delaware District of Columbia Florida most Georgia Indiana most Kentucky most Maine Maryland Massachusetts Michigan most New Hampshire New Jersey New York North Carolina Ohio Pennsylvania Rhode Island South Carolina Tennessee east Vermont Virginia West Virginia UTC 04 00 nbsp Anguilla nbsp Antigua and Barbuda nbsp Aruba nbsp Barbados nbsp Bolivia nbsp Brazil Amazonas most Mato Grosso Mato Grosso do Sul Rondonia Roraima nbsp British Virgin Islands nbsp Canada Quebec east nbsp Caribbean Netherlands nbsp Curacao nbsp Dominica nbsp Dominican Republic nbsp Grenada nbsp Guadeloupe nbsp Guyana nbsp Martinique nbsp Montserrat nbsp Puerto Rico nbsp Saint Barthelemy nbsp Saint Kitts and Nevis nbsp Saint Lucia nbsp Saint Martin nbsp Saint Vincent and the Grenadines nbsp Sint Maarten nbsp Trinidad and Tobago nbsp U S Virgin Islands nbsp Venezuela nbsp Bermuda nbsp Canada Labrador most New Brunswick Nova Scotia Prince Edward Island nbsp Chile most nbsp Greenland Pituffik Space Base nbsp Paraguay UTC 03 30 nbsp Canada Newfoundland Labrador southeast UTC 03 00 nbsp Argentina nbsp Brazil most nbsp Chile Magallanes Region nbsp Falkland Islands nbsp French Guiana nbsp Suriname nbsp Uruguay nbsp Saint Pierre and Miquelon UTC 02 00 nbsp Brazil Fernando de Noronha nbsp South Georgia and the South Sandwich Islands nbsp Greenland most UTC 01 00 nbsp Cape Verde nbsp Portugal Azores UTC 00 00 nbsp Burkina Faso nbsp Gambia nbsp Ghana nbsp Greenland National Park east coast nbsp Guinea nbsp Guinea Bissau nbsp Iceland nbsp Ivory Coast nbsp Liberia nbsp Mali nbsp Mauritania nbsp Saint Helena Ascension and Tristan da Cunha nbsp Senegal nbsp Sierra Leone nbsp Sao Tome and Principe nbsp Togo nbsp Faroe Islands nbsp Guernsey nbsp Ireland nbsp Isle of Man nbsp Jersey nbsp Portugal most nbsp Spain Canary Islands nbsp United Kingdom UTC 01 00 nbsp Algeria nbsp Angola nbsp Benin nbsp Cameroon nbsp Central African Republic nbsp Chad nbsp Congo nbsp Democratic Republic of the Congo Equateur Kinshasa Kongo Central Kwango Kwilu Mai Ndombe Mongala Nord Ubangi Sud Ubangi Tshuapa nbsp Equatorial Guinea nbsp Gabon nbsp Morocco a nbsp Niger nbsp Nigeria nbsp Tunisia nbsp Western Sahara a nbsp Albania nbsp Andorra nbsp Austria nbsp Belgium nbsp Bosnia and Herzegovina nbsp Croatia nbsp Czech Republic nbsp Denmark nbsp France metropolitan nbsp Germany nbsp Gibraltar nbsp Hungary nbsp Italy nbsp Kosovo nbsp Liechtenstein nbsp Luxembourg nbsp Malta nbsp Monaco nbsp Montenegro nbsp Netherlands European nbsp North Macedonia nbsp Norway nbsp Poland nbsp San Marino nbsp Serbia nbsp Slovakia nbsp Slovenia nbsp Spain most nbsp Sweden nbsp Switzerland nbsp Vatican City UTC 02 00 nbsp Botswana nbsp Burundi nbsp Democratic Republic of the Congo most nbsp Eswatini nbsp Lesotho nbsp Libya nbsp Malawi nbsp Mozambique nbsp Namibia nbsp Russia Kaliningrad nbsp Rwanda nbsp South Africa most nbsp South Sudan nbsp Sudan nbsp Zambia nbsp Zimbabwe nbsp Akrotiri and Dhekelia nbsp Bulgaria nbsp Cyprus nbsp Egypt nbsp Estonia nbsp Finland nbsp Greece nbsp Israel nbsp Latvia nbsp Lebanon nbsp Lithuania nbsp Moldova nbsp Northern Cyprus nbsp Palestine nbsp Romania nbsp Transnistria nbsp Ukraine most UTC 03 00 nbsp Abkhazia nbsp Bahrain nbsp Belarus nbsp Comoros nbsp Djibouti nbsp Eritrea nbsp Ethiopia nbsp French Southern and Antarctic Lands Scattered Islands 4 nbsp Iraq nbsp Jordan nbsp Kenya nbsp Kuwait nbsp Madagascar nbsp Mayotte nbsp Qatar nbsp Russia most of European part nbsp Saudi Arabia nbsp Somalia nbsp Somaliland nbsp South Africa Prince Edward Islands nbsp South Ossetia nbsp Syria nbsp Tanzania nbsp Turkey nbsp Uganda nbsp Ukraine occupied territories nbsp Yemen UTC 03 30 nbsp Iran UTC 04 00 nbsp Armenia nbsp Azerbaijan nbsp French Southern and Antarctic Lands Crozet Islands 4 nbsp Georgia nbsp Mauritius nbsp Oman nbsp Russia Astrakhan Samara Saratov Udmurtia Ulyanovsk nbsp Reunion nbsp Seychelles nbsp United Arab Emirates UTC 04 30 nbsp Afghanistan UTC 05 00 nbsp French Southern and Antarctic Lands Kerguelen Islands Saint Paul Island Amsterdam Island nbsp Heard Island and McDonald Islands nbsp Kazakhstan nbsp Maldives nbsp Pakistan nbsp Russia Bashkortostan Chelyabinsk Khanty Mansi Kurgan Orenburg Perm Sverdlovsk Tyumen Yamalia nbsp Tajikistan nbsp Turkmenistan nbsp Uzbekistan UTC 05 30 nbsp India nbsp Sri Lanka UTC 05 45 nbsp Nepal UTC 06 00 nbsp Bangladesh nbsp Bhutan nbsp British Indian Ocean Territory nbsp Kyrgyzstan nbsp Russia Omsk UTC 06 30 nbsp Cocos Keeling Islands nbsp Myanmar UTC 07 00 nbsp Cambodia nbsp Christmas Island nbsp Indonesia Sumatra Java West Kalimantan Central Kalimantan nbsp Laos nbsp Mongolia Bayan Olgii Khovd Uvs nbsp Russia Altai Krai Altai Republic Kemerovo Khakassia Krasnoyarsk Novosibirsk Tomsk Tuva nbsp Thailand nbsp Vietnam UTC 08 00 nbsp Australia Western Australia most nbsp Brunei nbsp China nbsp Hong Kong nbsp Indonesia South Kalimantan East Kalimantan North Kalimantan Sulawesi Lesser Sunda Islands nbsp Macau nbsp Malaysia nbsp Mongolia most nbsp Philippines nbsp Russia Buryatia Irkutsk nbsp Singapore nbsp Taiwan UTC 08 45 nbsp Australia Eucla UTC 09 00 nbsp East Timor nbsp Indonesia Maluku Islands Western New Guinea nbsp Japan nbsp North Korea nbsp Palau nbsp Russia Amur Sakha most Zabaykalsky nbsp South Korea UTC 09 30 nbsp Australia Northern Territory nbsp Australia South Australia Yancowinna County 5 UTC 10 00 nbsp Australia Queensland nbsp Guam nbsp Micronesia Chuuk Yap nbsp Northern Mariana Islands nbsp Papua New Guinea most nbsp Russia Jewish Khabarovsk Primorsky Sakha central east nbsp Australia Australian Capital Territory Jervis Bay Territory New South Wales most Tasmania Victoria UTC 10 30 nbsp Australia Lord Howe Island DST increase is 30 minutes UTC 11 00 nbsp Micronesia Kosrae Pohnpei nbsp New Caledonia nbsp Papua New Guinea Bougainville nbsp Russia Magadan Sakha east Sakhalin nbsp Solomon Islands nbsp Vanuatu nbsp Norfolk Island UTC 12 00 nbsp Fiji nbsp Kiribati Gilbert Islands nbsp Marshall Islands nbsp Nauru nbsp Russia Chukotka Kamchatka nbsp Tuvalu nbsp Wake Island nbsp Wallis and Futuna nbsp New Zealand most UTC 12 45 nbsp New Zealand Chatham Islands UTC 13 00 nbsp Kiribati Phoenix Islands nbsp Samoa nbsp Tokelau nbsp Tonga UTC 14 00 nbsp Kiribati Line IslandsHistoryThe apparent position of the Sun in the sky and thus solar time varies by location due to the spherical shape of the Earth This variation corresponds to four minutes of time for every degree of longitude so for example when it is solar noon in London it is about 10 minutes before solar noon in Bristol which is about 2 5 degrees to the west 6 The Royal Observatory Greenwich founded in 1675 established Greenwich Mean Time GMT the mean solar time at that location as an aid to mariners to determine longitude at sea providing a standard reference time while each location in England kept a different time Railway time Main article Railway time nbsp Plaque commemorating the Railway General Time Convention of 1883 in North America nbsp The control panel of the Time Zone Clock in front of Coventry Transport Museum In the 19th century as transportation and telecommunications improved it became increasingly inconvenient for each location to observe its own solar time In November 1840 the British Great Western Railway started using GMT kept by portable chronometers 7 failed verification This practice was soon followed by other railway companies in Great Britain and became known as Railway Time Around August 23 1852 time signals were first transmitted by telegraph from the Royal Observatory By 1855 98 of Great Britain s public clocks were using GMT but it was not made the island s legal time until August 2 1880 Some British clocks from this period have two minute hands one for the local time and one for GMT 8 On November 2 1868 the then British Colony of New Zealand officially adopted a standard time to be observed throughout the colony 9 It was based on longitude 172 30 east of Greenwich that is 11 hours 30 minutes ahead of GMT This standard was known as New Zealand Mean Time 10 nbsp 1913 time zone map of the United States showing boundaries very different from today Timekeeping on North American railroads in the 19th century was complex Each railroad used its own standard time usually based on the local time of its headquarters or most important terminus and the railroad s train schedules were published using its own time Some junctions served by several railroads had a clock for each railroad each showing a different time 11 Around 1863 Charles F Dowd proposed a system of hourly standard time zones for North American railroads although he published nothing on the matter at that time and did not consult railroad officials until 1869 In 1870 he proposed four ideal time zones having north south borders the first centered on Washington D C but by 1872 the first was centered on meridian 75 west of Greenwich with natural borders such as sections of the Appalachian Mountains Dowd s system was never accepted by North American railroads Chief meteorologist at the United States Weather Bureau Cleveland Abbe divided the United States into four standard time zones for consistency among the weather stations In 1879 he published a paper titled Report on Standard Time 12 In 1883 he convinced North American railroad companies to adopt his time zone system In 1884 Britain which had already adopted its own standard time system for England Scotland and Wales helped gather international consent for global time In time the American government influenced in part by Abbe s 1879 paper adopted the time zone system 13 It was a version proposed by William F Allen the editor of the Traveler s Official Railway Guide 14 The borders of its time zones ran through railroad stations often in major cities For example the border between its Eastern and Central time zones ran through Detroit Buffalo Pittsburgh Atlanta and Charleston It was inaugurated on Sunday November 18 1883 also called The Day of Two Noons 15 when each railroad station clock was reset as standard time noon was reached within each time zone The North American zones were named Intercolonial Eastern Central Mountain and Pacific Within a year 85 of all cities with populations over 10 000 about 200 cities were using standard time 16 A notable exception was Detroit located about halfway between the meridians of Eastern and Central time which kept local time until 1900 then tried Central Standard Time local mean time and Eastern Standard Time EST before a May 1915 ordinance settled on EST and was ratified by popular vote in August 1916 The confusion of times came to an end when standard time zones were formally adopted by the U S Congress in the Standard Time Act of March 19 1918 Worldwide time zones World time redirects here For the global time standard see Universal Time Italian mathematician Quirico Filopanti introduced the idea of a worldwide system of time zones in his book Miranda published in 1858 He proposed 24 hourly time zones which he called longitudinal days the first centred on the meridian of Rome He also proposed a universal time to be used in astronomy and telegraphy However his book attracted no attention until long after his death 17 18 Scottish born Canadian Sir Sandford Fleming proposed a worldwide system of time zones in 1876 see Sandford Fleming Inventor of worldwide standard time The proposal divided the world into twenty four time zones labeled A Y skipping J each one covering 15 degrees of longitude All clocks within each zone would be set to the same time as the others but differed by one hour from those in the neighboring zones 19 He advocated his system at several international conferences including the International Meridian Conference where it received some consideration The system has not been directly adopted but some maps divide the world into 24 time zones and assign letters to them similarly to Fleming s system 20 nbsp World map of time zones in 1928 By about 1900 almost all inhabited places on Earth had adopted a standard time zone but only some of them used an hourly offset from GMT Many applied the time at a local astronomical observatory to an entire country without any reference to GMT It took many decades before all time zones were based on some standard offset from GMT or Coordinated Universal Time UTC By 1929 the majority of countries had adopted hourly time zones though some countries such as Iran India Myanmar and parts of Australia had time zones with a 30 minute offset Nepal was the last country to adopt a standard offset shifting slightly to UTC 05 45 in 1986 21 All nations currently use standard time zones for secular purposes but not all of them apply the concept as originally conceived Several countries and subdivisions use half hour or quarter hour deviations from standard time Some countries such as China and India use a single time zone even though the extent of their territory far exceeds the ideal 15 of longitude for one hour other countries such as Spain and Argentina use standard hour based offsets but not necessarily those that would be determined by their geographical location The consequences in some areas can affect the lives of local citizens and in extreme cases contribute to larger political issues such as in the western reaches of China 22 In Russia which has 11 time zones two time zones were removed in 2010 23 24 and reinstated in 2014 25 NotationISO 8601 Main article ISO 8601 ISO 8601 is a standard established by the International Organization for Standardization defining methods of representing dates and times in textual form including specifications for representing time zones If a time is in Coordinated Universal Time UTC a Z is added directly after the time without a separating space Z is the zone designator for the zero UTC offset 09 30 UTC is therefore represented as 09 30Z or 0930Z Likewise 14 45 15 UTC is written as 14 45 15Z or 144515Z 26 UTC time is also known as Zulu time since Zulu is a phonetic alphabet code word for the letter Z 26 Offsets from UTC are written in the format hh mm hhmm or hh either hours ahead or behind UTC For example if the time being described is one hour ahead of UTC such as the time in Germany during the winter the zone designator would be 01 00 0100 or simply 01 This numeric representation of time zones is appended to local times in the same way that alphabetic time zone abbreviations or Z as above are appended The offset from UTC changes with daylight saving time e g a time offset in Chicago which is in the North American Central Time Zone is 06 00 for the winter Central Standard Time and 05 00 for the summer Central Daylight Time 27 Abbreviations Main article List of time zone abbreviations Time zones are often represented by alphabetic abbreviations such as EST WST and CST but these are not part of the international time and date standard ISO 8601 Such designations can be ambiguous for example CST can mean North American Central Standard Time UTC 06 00 Cuba Standard Time UTC 05 00 and China Standard Time UTC 08 00 and it is also a widely used variant of ACST Australian Central Standard Time UTC 09 30 28 ConversionsConversion between time zones obeys the relationship time in zone A UTC offset for zone A time in zone B UTC offset for zone B in which each side of the equation is equivalent to UTC The conversion equation can be rearranged to time in zone B time in zone A UTC offset for zone A UTC offset for zone B For example the New York Stock Exchange opens at 09 30 EST UTC offset 05 00 In California PST UTC offset 08 00 and India IST UTC offset 05 30 the New York Stock Exchange opens at time in California 09 30 05 00 08 00 06 30 time in India 09 30 05 00 05 30 20 00 These calculations become more complicated near the time switch to or from daylight saving time as the UTC offset for the area becomes a function of UTC time The time differences may also result in different dates For example when it is 22 00 on Monday in Egypt UTC 02 00 it is 01 00 on Tuesday in Pakistan UTC 05 00 The table Time of day by zone gives an overview on the time relations between different zones Time of day by zone UTC offset Monday UTC 12 00 00 00 01 00 02 00 03 00 04 00 05 00 06 00 07 00 08 00 09 00 10 00 11 00 12 00 13 00 14 00 15 00 16 00 17 00 18 00 19 00 20 00 21 00 22 00 23 00 UTC 11 00 01 00 02 00 03 00 04 00 05 00 06 00 07 00 08 00 09 00 10 00 11 00 12 00 13 00 14 00 15 00 16 00 17 00 18 00 19 00 20 00 21 00 22 00 23 00 00 00 UTC 10 00 02 00 03 00 04 00 05 00 06 00 07 00 08 00 09 00 10 00 11 00 12 00 13 00 14 00 15 00 16 00 17 00 18 00 19 00 20 00 21 00 22 00 23 00 00 00 01 00 UTC 09 30 02 30 03 30 04 30 05 30 06 30 07 30 08 30 09 30 10 30 11 30 12 30 13 30 14 30 15 30 16 30 17 30 18 30 19 30 20 30 21 30 22 30 23 30 00 30 01 30 UTC 09 00 03 00 04 00 05 00 06 00 07 00 08 00 09 00 10 00 11 00 12 00 13 00 14 00 15 00 16 00 17 00 18 00 19 00 20 00 21 00 22 00 23 00 00 00 01 00 02 00 UTC 08 00 04 00 05 00 06 00 07 00 08 00 09 00 10 00 11 00 12 00 13 00 14 00 15 00 16 00 17 00 18 00 19 00 20 00 21 00 22 00 23 00 00 00 01 00 02 00 03 00 UTC 07 00 05 00 06 00 07 00 08 00 09 00 10 00 11 00 12 00 13 00 14 00 15 00 16 00 17 00 18 00 19 00 20 00 21 00 22 00 23 00 00 00 01 00 02 00 03 00 04 00 UTC 06 00 06 00 07 00 08 00 09 00 10 00 11 00 12 00 13 00 14 00 15 00 16 00 17 00 18 00 19 00 20 00 21 00 22 00 23 00 00 00 01 00 02 00 03 00 04 00 05 00 UTC 05 00 07 00 08 00 09 00 10 00 11 00 12 00 13 00 14 00 15 00 16 00 17 00 18 00 19 00 20 00 21 00 22 00 23 00 00 00 01 00 02 00 03 00 04 00 05 00 06 00 UTC 04 00 08 00 09 00 10 00 11 00 12 00 13 00 14 00 15 00 16 00 17 00 18 00 19 00 20 00 21 00 22 00 23 00 00 00 01 00 02 00 03 00 04 00 05 00 06 00 07 00 UTC 03 30 08 30 09 30 10 30 11 30 12 30 13 30 14 30 15 30 16 30 17 30 18 30 19 30 20 30 21 30 22 30 23 30 00 30 01 30 02 30 03 30 04 30 05 30 06 30 07 30 UTC 03 00 09 00 10 00 11 00 12 00 13 00 14 00 15 00 16 00 17 00 18 00 19 00 20 00 21 00 22 00 23 00 00 00 01 00 02 00 03 00 04 00 05 00 06 00 07 00 08 00 UTC 02 30 09 30 10 30 11 30 12 30 13 30 14 30 15 30 16 30 17 30 18 30 19 30 20 30 21 30 22 30 23 30 00 30 01 30 02 30 03 30 04 30 05 30 06 30 07 30 08 30 UTC 02 00 10 00 11 00 12 00 13 00 14 00 15 00 16 00 17 00 18 00 19 00 20 00 21 00 22 00 23 00 00 00 01 00 02 00 03 00 04 00 05 00 06 00 07 00 08 00 09 00 UTC 01 00 11 00 12 00 13 00 14 00 15 00 16 00 17 00 18 00 19 00 20 00 21 00 22 00 23 00 00 00 01 00 02 00 03 00 04 00 05 00 06 00 07 00 08 00 09 00 10 00 UTC 00 00 12 00 13 00 14 00 15 00 16 00 17 00 18 00 19 00 20 00 21 00 22 00 23 00 00 00 01 00 02 00 03 00 04 00 05 00 06 00 07 00 08 00 09 00 10 00 11 00 UTC 01 00 13 00 14 00 15 00 16 00 17 00 18 00 19 00 20 00 21 00 22 00 23 00 00 00 01 00 02 00 03 00 04 00 05 00 06 00 07 00 08 00 09 00 10 00 11 00 12 00 UTC 02 00 14 00 15 00 16 00 17 00 18 00 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17 45 18 45 19 45 20 45 21 45 22 45 23 45 UTC 13 00 01 00 02 00 03 00 04 00 05 00 06 00 07 00 08 00 09 00 10 00 11 00 12 00 13 00 14 00 15 00 16 00 17 00 18 00 19 00 20 00 21 00 22 00 23 00 00 00 UTC 13 45 01 45 02 45 03 45 04 45 05 45 06 45 07 45 08 45 09 45 10 45 11 45 12 45 13 45 14 45 15 45 16 45 17 45 18 45 19 45 20 45 21 45 22 45 23 45 00 45 UTC 14 00 02 00 03 00 04 00 05 00 06 00 07 00 08 00 09 00 10 00 11 00 12 00 13 00 14 00 15 00 16 00 17 00 18 00 19 00 20 00 21 00 22 00 23 00 00 00 01 00 UTC offset Tuesday WednesdayNautical time zonesMain article Nautical time Since the 1920s a nautical standard time system has been in operation for ships on the high seas As an ideal form of the terrestrial time zone system nautical time zones consist of gores of 15 offset from GMT by a whole number of hours A nautical date line follows the 180th meridian bisecting one 15 gore into two 7 5 gores that differ from GMT by 12 hours 29 30 31 However in practice each ship may choose what time to observe at each location Ships may decide to adjust their clocks at a convenient time usually at night not exactly when they cross a certain longitude 32 Some ships simply remain on the time of the departing port during the whole trip 33 Skewing of time zones nbsp Difference between sun time and clock time during daylight saving time 1h 30 min behind 0h 30m 1h 30 m ahead 2h 30 m ahead 3h 30 m ahead nbsp DST observed DST formerly observed DST never observed Ideal time zones such as nautical time zones are based on the mean solar time of a particular meridian in the middle of that zone with boundaries located 7 5 degrees east and west of the meridian In practice however many time zone boundaries are drawn much farther to the west and some countries are located entirely outside their ideal time zones For example even though the Prime Meridian 0 passes through Spain and France they use the mean solar time of 15 degrees east Central European Time rather than 0 degrees Greenwich Mean Time France previously used GMT but was switched to CET Central European Time during the German occupation of the country during World War II and did not switch back after the war 34 Similarly prior to World War II the Netherlands observed Amsterdam Time which was twenty minutes ahead of Greenwich Mean Time They were obliged to follow German time during the war and kept it thereafter In the mid 1970s the Netherlands as other European states began observing daylight saving summer time One reason to draw time zone boundaries far to the west of their ideal meridians is to allow the more efficient use of afternoon sunlight 35 Some of these locations also use daylight saving time DST further increasing the difference to local solar time As a result in summer solar noon in the Spanish city of Vigo occurs at 14 41 clock time This westernmost area of continental Spain never experiences sunset before 18 00 clock time even in winter despite lying 42 degrees north of the equator 36 Near the summer solstice Vigo has sunset times after 22 00 similar to those of Stockholm which is in the same time zone and 17 degrees farther north Stockholm has much earlier sunrises though 37 A more extreme example is Nome Alaska which is at 165 24 W longitude just west of center of the idealized Samoa Time Zone 165 W Nevertheless Nome observes Alaska Time 135 W with DST so it is slightly more than two hours ahead of the sun in winter and over three in summer 38 Kotzebue Alaska also near the same meridian but north of the Arctic Circle has two sunsets on the same day in early August one shortly after midnight at the start of the day and the other shortly before midnight at the end of the day 39 China extends as far west as 73 E but all parts of it use UTC 08 00 120 E so solar noon can occur as late as 15 00 in western portions of China such as Xinjiang 40 The Afghanistan China border marks the greatest terrestrial time zone difference on Earth with a 3 5 hour difference between Afghanistan s UTC 4 30 and China s UTC 08 00 nbsp A visualization of the mismatch between clock time and solar time in different locations In blue areas clock time lags behind solar time in red areas the reverse is true The two are synchronized in the white areas Daylight saving timeMain article Daylight saving time Many countries and sometimes just certain regions of countries adopt daylight saving time DST also known as summer time during part of the year This typically involves advancing clocks by an hour near the start of spring and adjusting back in autumn spring forward fall back Modern DST was first proposed in 1907 and was in widespread use in 1916 as a wartime measure aimed at conserving coal Despite controversy many countries have used it off and on since then details vary by location and change occasionally Countries around the equator usually do not observe daylight saving time since the seasonal difference in sunlight there is minimal Computer systemsMany computer operating systems include the necessary support for working with all or almost all possible local times based on the various time zones Internally operating systems typically use UTC as their basic time keeping standard while providing services for converting local times to and from UTC and also the ability to automatically change local time conversions at the start and end of daylight saving time in the various time zones See the article on daylight saving time for more details on this aspect Web servers presenting web pages primarily for an audience in a single time zone or a limited range of time zones typically show times as a local time perhaps with UTC time in brackets More internationally oriented websites may show times in UTC only or using an arbitrary time zone For example the international English language version of CNN includes GMT and Hong Kong Time 41 whereas the US version shows Eastern Time 42 US Eastern Time and Pacific Time are also used fairly commonly on many US based English language websites with global readership The format is typically based in the W3C Note datetime Email systems and other messaging systems IRC chat etc 43 time stamp messages using UTC or else include the sender s time zone as part of the message allowing the receiving program to display the message s date and time of sending in the recipient s local time Database records that include a time stamp typically use UTC especially when the database is part of a system that spans multiple time zones The use of local time for time stamping records is not recommended for time zones that implement daylight saving time because once a year there is a one hour period when local times are ambiguous Calendar systems nowadays usually tie their time stamps to UTC and show them differently on computers that are in different time zones That works when having telephone or internet meetings It works less well when travelling because the calendar events are assumed to take place in the time zone the computer or smartphone was on when creating the event The event can be shown at the wrong time For example if a New Yorker plans to meet someone in Los Angeles at 9 am and makes a calendar entry at 9 am which the computer assumes is New York time the calendar entry will be at 6 am if taking the computer s time zone There is also an option in newer versions of Microsoft Outlook to enter the time zone in which an event will happen but often not in other calendar systems Calendaring software must also deal with daylight saving time DST If for political reasons the begin and end dates of daylight saving time are changed calendar entries should stay the same in local time even though they may shift in UTC time In Microsoft Outlook time stamps are therefore stored and communicated without DST offsets 44 Hence an appointment in London at noon in the summer will be represented as 12 00 UTC 00 00 even though the event will actually take place at 13 00 UTC In Google Calendar calendar events are stored in UTC although shown in local time and might be changed by a time zone changes 45 although normal daylight saving start and end are compensated for similar to much other calendar software Operating systems Unix Main article Unix time Unix like systems including Linux and macOS keep system time in Unix time format representing the number of seconds excluding leap seconds that have elapsed since 00 00 00 Coordinated Universal Time UTC on Thursday January 1 1970 46 Unix time is usually converted to local time when displayed to the user and times specified by the user in local time are converted to Unix time The conversion takes into account the time zone and daylight saving time rules by default the time zone and daylight saving time rules are set up when the system is configured though individual processes can specify time zones and daylight saving time rules using the TZ environment variable 47 This allows users in multiple time zones or in the same time zone but with different daylight saving time rules to use the same computer with their respective local times displayed correctly to each user Time zone and daylight saving time rule information most commonly comes from the IANA time zone database In fact many systems including anything using the GNU C Library a C library based on the BSD C library or the System V Release 4 C library can make use of this database Microsoft Windows Windows based computer systems prior to Windows 95 and Windows NT used local time but Windows 95 and later and Windows NT base system time on UTC 48 49 They allow a program to fetch the system time as UTC represented as a year month day hour minute second and millisecond 50 51 Windows 95 and later and Windows NT 3 5 and later also allow the system time to be fetched as a count of 100 ns units since 1601 01 01 00 00 00 UTC 52 53 The system registry contains time zone information that includes the offset from UTC and rules that indicate the start and end dates for daylight saving in each zone Interaction with the user normally uses local time and application software is able to calculate the time in various zones Terminal Servers allow remote computers to redirect their time zone settings to the Terminal Server so that users see the correct time for their time zone in their desktop application sessions Terminal Services uses the server base time on the Terminal Server and the client time zone information to calculate the time in the session Programming languages Java While most application software will use the underlying operating system for time zone and daylight saving time rule information the Java Platform from version 1 3 1 has maintained its own database of time zone and daylight saving time rule information This database is updated whenever time zone or daylight saving time rules change Oracle provides an updater tool for this purpose 54 As an alternative to the information bundled with the Java Platform programmers may choose to use the Joda Time library 55 This library includes its own data based on the IANA time zone database 56 As of Java 8 there is a new date and time API that can help with converting times 57 JavaScript Traditionally there was very little in the way of time zone support for JavaScript Essentially the programmer had to extract the UTC offset by instantiating a time object getting a GMT time from it and differencing the two This does not provide a solution for more complex daylight saving variations such as divergent DST directions between northern and southern hemispheres ECMA 402 the standard on Internationalization API for JavaScript provides ways of formatting Time Zones 58 However due to size constraint some implementations or distributions do not include it 59 Perl The DateTime object in Perl supports all entries in the IANA time zone database and includes the ability to get set and convert between time zones 60 PHP The DateTime objects and related functions have been compiled into the PHP core since 5 2 This includes the ability to get and set the default script time zone and DateTime is aware of its own time zone internally PHP net provides extensive documentation on this 61 As noted there the most current time zone database can be implemented via the PECL timezonedb Python The standard module datetime included with Python stores and operates on the time zone information class tzinfo The third party pytz module provides access to the full IANA time zone database 62 Negated time zone offset in seconds is stored time timezone and time altzone attributes From Python 3 9 the zoneinfo module introduces timezone management without need for third party module 63 Smalltalk Each Smalltalk dialect comes with its own built in classes for dates times and timestamps only a few of which implement the DateAndTime and Duration classes as specified by the ANSI Smalltalk Standard VisualWorks provides a TimeZone class that supports up to two annually recurring offset transitions which are assumed to apply to all years same behavior as Windows time zones Squeak provides a Timezone class that does not support any offset transitions Dolphin Smalltalk does not support time zones at all For full support of the tz database zoneinfo in a Smalltalk application including support for any number of annually recurring offset transitions and support for different intra year offset transition rules in different years the third party open source ANSI Smalltalk compliant Chronos Date Time Library is available for use with any of the following Smalltalk dialects VisualWorks Squeak Gemstone or Dolphin 64 Time in outer spaceOrbiting spacecraft may experience many sunrises and sunsets or none in a 24 hour period Therefore it is not possible to calibrate the time with respect to the Sun and still respect a 24 hour sleep wake cycle A common practice for space exploration is to use the Earth based time of the launch site or mission control synchronizing the sleeping cycles of the crew and controllers The International Space Station normally uses Greenwich Mean Time GMT 65 66 Timekeeping on Mars can be more complex since the planet has a solar day of approximately 24 hours and 40 minutes known as a sol Earth controllers for some Mars missions have synchronized their sleep wake cycles with the Martian day because solar powered rover activity on the surface was tied to periods of light and dark 67 See also nbsp Geography portal nbsp World portal Daylight saving time ISO 8601 Jet lag Lists of time zones Metric time Time by country Time in Europe Time zone abolition World clock International Date LineNotes a b Observes UTC 00 00 around Ramadan 1 2 3 References Morocco Re Introduces Clock Changes for Ramadan 2019 Timeanddate com April 19 2019 Archived from the original on December 28 2020 Time Zone in Casablanca Morocco Timeanddate com Archived from the original on March 30 2021 Time Zone in El Aaiun Western Sahara Timeanddate com Archived from the original on February 14 2021 a b Decret nº 2017 292 du 6 mars 2017 relatif au temps legal francais Decree no 2017 292 of 6 March 2017 relative to French legal time in French Legifrance March 8 2017 Archived from the original on December 2 2020 Standard Time Act 1987 No 149 New South Wales Government Retrieved February 29 2024 Latitude and Longitude of World Cities Infoplease Archived from the original on May 24 2011 Retrieved April 18 2012 WESTMINSTER MEDICAL SOCIETY Saturday November 21 1840 The Lancet 35 901 383 December 1840 doi 10 1016 s0140 6736 00 59842 0 ISSN 0140 6736 Archived from the original on March 30 2021 Retrieved January 27 2021 Bristol Time GreenwichMeanTime com Archived from the original on June 28 2006 Retrieved December 5 2011 Telegraph line laid across Cook Strait New Zealand Ministry for Culture and Heritage Archived from the original on February 18 2020 Retrieved January 5 2020 Our Time How we got it New Zealand s Method A Lead to the World Papers Past Evening Post p 10 Archived from the original on 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Retrieved March 24 2022 Reprinted in 1889 Time reckoning for the twentieth century at the Internet Archive Stromberg Joseph November 18 2011 Sandford Fleming Sets the World s Clock Smithsonian Magazine Archived from the original on March 24 2022 Retrieved March 24 2022 Time Zone amp Clock Changes in Kathmandu Nepal timeanddate com Archived from the original on January 22 2021 Retrieved December 1 2020 Schiavenza Matt November 5 2013 China Only Has One Time Zone and That s a Problem The Atlantic Archived from the original on August 22 2018 Retrieved August 22 2018 Russia Reduces Number of Time Zones TimeAndDate com March 23 2010 Archived from the original on August 9 2020 Retrieved May 31 2020 About Time Huge country nine time zones Video BBC March 22 2011 Archived from the original on February 13 2019 Retrieved February 12 2019 Russian clocks to retreat again in winter 11 time zones return Reuters July 2014 Archived from the original on October 28 2020 Retrieved October 25 2020 a b Z 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GetSystemTimeAsFileTime function Windows Microsoft Learn Retrieved April 23 2024 Timezone Updater Tool Oracle Java Technologies Archived from the original on November 24 2011 Retrieved December 5 2011 Joda Time Joda time sourceforge net Archived from the original on December 3 2011 Retrieved December 5 2011 tz database Twinsun com December 26 2007 Archived from the original on June 23 2012 Retrieved December 5 2011 Java 8 Date Time ECMAScript 2015 Internationalization API Specification ecma international org ECMA International June 2015 Archived from the original on October 26 2019 Retrieved September 4 2019 Internationalization Support Node js v12 10 0 Documentation Archived from the original on August 28 2019 Retrieved September 4 2019 DateTime METACPAN Archived from the original on March 29 2014 Retrieved April 14 2014 DateTime Php net Archived from the original on November 22 2011 Retrieved December 5 2011 pytz module Pytz sourceforge net Archived from the original on November 30 2011 Retrieved December 5 2011 zoneinfo module www python org Archived from the original on February 7 2021 Retrieved February 8 2021 Chronos Date Time Library Archived April 5 2014 at the Wayback Machine Ask the Crew STS 111 National Aeronautics and Space Administration June 19 2002 Archived from the original on September 28 2015 Retrieved September 10 2015 Lu Ed September 8 2003 Day in the Life National Aeronautics and Space Administration Archived from the original on September 1 2012 Retrieved September 10 2015 New Tricks Could Help Mars Rover Team Live on Mars Time Archived August 12 2014 at the Wayback Machine Megan Gannon Space com September 28 2012 SourcesAsimov Isaac 1964 Abbe Cleveland Asimov s Biographical Encyclopedia of Science and Technology The Living Stories of More than 1000 Great Scientists from the Age of Greece to the Space Age Garden City NY Doubleday amp Company Inc pp 343 344 LCCN 64016199 Debus Allen G ed 1968 Abbe Cleveland World Who s Who in Science A Biographical Dictionary of Notable Scientists from Antiquity to the Present 1st ed Chicago IL A N Marquis Company ISBN 0 8379 1001 3 LCCN 68056149 Further readingBiswas Soutik February 12 2019 How India s single time zone is hurting its people BBC News Retrieved February 12 2019 Maulik Jagnani economist at Cornell University January 15 2019 PoorSleep Sunset Time and Human Capital Production Job Market Paper Retrieved February 12 2019 Time Bandits The countries rebelling against GMT Video BBC News August 14 2015 Retrieved February 12 2019 How time zones confused the world BBC News August 7 2015 Retrieved February 12 2019 Lane Megan May 10 2011 How does a country change its time zone BBC News Retrieved February 12 2019 A brief history of time zones Video BBC News March 24 2011 Retrieved February 12 2019 The Time Zone Information Format TZif doi 10 17487 RFC8536 RFC 8536 External links nbsp Wikivoyage has a travel guide for Time zones nbsp Media related to Time zones at Wikimedia Commons Retrieved from https en wikipedia org w index php title Time zone amp oldid 1220459330, wikipedia, wiki, book, books, library,

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