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Time zone

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Time zones of the world
Time zones of the world

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.

All time zones are defined as offsets from Coordinated Universal Time (UTC), ranging from UTC−12:00 to UTC+14:00. The offsets are usually a whole number of hours, but a few zones are offset by an additional 30 or 45 minutes, such as in India, South Australia and Nepal.

Some areas of higher latitude use daylight saving time for about half of the year, typically by adding one hour to local time during spring and summer.

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Standard time

Standard time

Standard time is the synchronisation of clocks within a geographical region to a single time standard, rather than a local mean time standard. Generally, standard time agrees with the local mean time at some meridian that passes through the region, often near the centre of the region. Historically, standard time was established during the 19th century to aid weather forecasting and train travel. Applied globally in the 20th century, the geographical regions became time zones. The standard time in each time zone has come to be defined as an offset from Universal Time. A further offset is applied for part of the year in regions with daylight saving time.

Commerce

Commerce

Commerce is the large-scale organized system of activities, functions, procedures and institutions which directly and indirectly contributes to the transfer of goods and services on a large scale and at the right time, place, quantity and price from the original producers to the final consumers within local, regional, national or international economies More specifically, commerce is not business, but rather the part of business which is related to the movement and distribution of finished or intermediate goods and services from the primary manufacturers to the end customers on a large scale, as opposed to the sourcing of raw materials and manufacturing of those goods.

Social

Social

Social organisms, including human(s), live collectively in interacting populations. This interaction is considered social whether they are aware of it or not, and whether the exchange is voluntary or not.

Country

Country

A country is a distinct part of the world, such as a state, nation, or other political entity. It may be a sovereign state or make up one part of a larger state. For example, the country of Japan is an independent, sovereign state, while the country of Wales is a component of a multi-part sovereign state, the United Kingdom. A country may be a historically sovereign area, a currently sovereign territory with a unified government, or a non-sovereign geographic region associated with certain distinct political, ethnic, or cultural characteristics.

Administrative division

Administrative division

Administrative division, administrative unit, country subdivision, administrative region, subnational entity, constituent state, as well as many similar terms, are generic names for geographical areas into which a particular, independent sovereign state (country) is divided. Such a unit usually has an administrative authority with the power to take administrative or policy decisions for its area.

Longitude

Longitude

Longitude is a geographic coordinate that specifies the east–west position of a point on the surface of the Earth, or another celestial body. It is an angular measurement, usually expressed in degrees and denoted by the Greek letter lambda (λ). Meridians are semicircular lines running from pole to pole that connect points with the same longitude. The prime meridian defines 0° longitude; by convention the International Reference Meridian for the Earth passes near the Royal Observatory in Greenwich, England on the island of Great Britain. Positive longitudes are east of the prime meridian, and negative ones are west.

Coordinated Universal Time

Coordinated Universal Time

Coordinated Universal Time or UTC is the primary time standard by which the world regulates clocks and time. It is within about one second of mean solar time at 0° longitude and is not adjusted for daylight saving time. It is effectively a successor to Greenwich Mean Time (GMT).

Indian Standard Time

Indian Standard Time

Indian Standard Time (IST), sometimes also called India Standard Time, is the time zone observed throughout India, with a time offset of UTC+05:30. India does not observe daylight saving time or other seasonal adjustments. In military and aviation time, IST is designated E†. It is indicated as Asia/Kolkata in the IANA time zone database.

Latitude

Latitude

In geography, latitude is a coordinate that specifies the north–south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north pole, with 0° at the Equator. Lines of constant latitude, or parallels, run east–west as circles parallel to the equator. Latitude and longitude are used together as a coordinate pair to specify a location on the surface of the Earth.

Daylight saving time

Daylight saving time

Daylight saving time (DST), also referred to as daylight savings time, daylight time, or summer time, is the practice of advancing clocks during warmer months so that darkness falls at a later clock time. The typical implementation of DST is to set clocks forward by one hour in either the late winter or spring, and to set clocks back by one hour in the fall to return to standard time. As a result, there is one 23-hour day in early spring and one 25-hour day in the middle of autumn.

Spring (season)

Spring (season)

Spring, also known as springtime, is one of the four temperate seasons, succeeding winter and preceding summer. There are various technical definitions of spring, but local usage of the term varies according to local climate, cultures and customs. When it is spring in the Northern Hemisphere, it is autumn in the Southern Hemisphere and vice versa. At the spring equinox, days and nights are approximately twelve hours long, with daytime length increasing and nighttime length decreasing as the season progresses until the Summer Solstice in June and December.

Summer

Summer

Summer is the hottest of the four temperate seasons, occurring after spring and before autumn. At or centred on the summer solstice, daylight hours are longest and darkness hours are shortest, with day length decreasing as the season progresses after the solstice. The earliest sunrises and latest sunsets also occur near the date of the solstice. The date of the beginning of summer varies according to climate, tradition, and culture. When it is summer in the Northern Hemisphere, it is winter in the Southern Hemisphere, and vice versa.

List of UTC offsets

Time zones of the world
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
 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: Colorado, Idaho (most), Kansas (west), Montana, Nebraska (panhandle), New Mexico, Nevada (West Wendover), 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)
UTC−05:00
UTC−04:00  Bermuda
 Canada: Labrador (most), New Brunswick, Nova Scotia, Prince Edward Island
 Chile (most)
 Greenland: Thule Air Base
 Paraguay
UTC−03:30  Canada: Newfoundland, Labrador (southeast)
UTC−03:00  Greenland (most)
 Saint Pierre and Miquelon
UTC−02:00  Brazil: Fernando de Noronha
 South Georgia and the South Sandwich Islands
UTC−01:00  Cape Verde
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
UTC+10:00  Australia: Australian Capital Territory, Jervis Bay Territory, New South Wales (most), Tasmania, Victoria
UTC+10:30  Australia: Lord Howe Island
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
  1. ^ a b Observes UTC±00:00 around Ramadan.[1][2][3]

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Lord Howe Island

Lord Howe Island

Lord Howe Island is an irregularly crescent-shaped volcanic remnant in the Tasman Sea between Australia and New Zealand, part of the Australian state of New South Wales. It lies 600 km (320 nmi) directly east of mainland Port Macquarie, 780 km (420 nmi) northeast of Sydney, and about 900 km (490 nmi) southwest of Norfolk Island. It is about 10 km (6.2 mi) long and between 0.3 and 2.0 km wide with an area of 14.55 km2, though just 3.98 km2 of that comprise the low-lying developed part of the island.

California

California

California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2 million residents across a total area of approximately 163,696 square miles (423,970 km2), it is the most populous U.S. state and the third-largest by area. It is also the most populated subnational entity in North America and the 34th most populous in the world. The Greater Los Angeles and San Francisco Bay areas are the nation's second and fifth most populous urban regions respectively, with the former having more than 18.7 million residents and the latter having over 9.6 million. Sacramento is the state's capital, while Los Angeles is the most populous city in the state and the second most populous city in the country. San Francisco is the second most densely populated major city in the country. Los Angeles County is the country's most populous, while San Bernardino County is the largest county by area in the country. California borders Oregon to the north, Nevada and Arizona to the east, the Mexican state of Baja California to the south; and it has a coastline along the Pacific Ocean to the west.

UTC−07:00

UTC−07:00

UTC−07:00 is an identifier for a time offset from UTC of −07:00. In North America, it is observed in the Mountain Time Zone during standard time, and in the Pacific Time Zone during the other eight months. Some locations use it year-round.

UTC+01:00

UTC+01:00

UTC+01:00 is an identifier for a time offset from UTC of +01:00. In ISO 8601, the associated time would be written as 2019-02-07T23:28:34+01:00. This time is used in:Central European Time West Africa Time Western European Summer Time British Summer Time Irish Standard Time

Baker Island

Baker Island

Baker Island, formerly known as New Nantucket, is an uninhabited atoll just north of the Equator in the central Pacific Ocean about 3,090 km (1,920 mi) southwest of Honolulu. The island lies almost halfway between Hawaii and Australia. Its nearest neighbor is Howland Island, 42 mi (68 km) to the north-northwest; both have been claimed as territories of the United States since 1857, though the United Kingdom considered them part of the British Empire between 1897 and 1936.

Howland Island

Howland Island

Howland Island is an uninhabited coral island located just north of the equator in the central Pacific Ocean, about 1,700 nautical miles (3,100 km) southwest of Honolulu. The island lies almost halfway between Hawaii and Australia and is an unorganized, unincorporated territory of the United States. Together with Baker Island it forms part of the Phoenix Islands. For statistical purposes, Howland is grouped as one of the United States Minor Outlying Islands. The island has an elongated cucumber-shape on a north–south axis, 1.40 by 0.55 miles, and covers 1 square mile.

Jarvis Island

Jarvis Island

Jarvis Island is an uninhabited 4.5 km2 (1.7 sq mi) coral island located in the South Pacific Ocean, about halfway between Hawaii and the Cook Islands. It is an unincorporated, unorganized territory of the United States, administered by the United States Fish and Wildlife Service of the United States Department of the Interior as part of the National Wildlife Refuge system. Unlike most coral atolls, the lagoon on Jarvis is wholly dry.

Kingman Reef

Kingman Reef

Kingman Reef is a largely submerged, uninhabited, triangle-shaped reef, geologically an atoll, 9.0 nmi (20 km) east-west and 4.5 nmi (8 km) north-south, in the North Pacific Ocean, roughly halfway between the Hawaiian Islands and American Samoa. It has an area of 3 hectares and is one of the unincorporated territories of the United States in Oceania. The reef is administered by the United States Fish and Wildlife Service as the Kingman Reef National Wildlife Refuge.

Midway Atoll

Midway Atoll

Midway Atoll is a 2.4 sq mi (6.2 km2) atoll in the North Pacific Ocean. Midway Atoll is an insular area of the United States and is an unorganized and unincorporated territory. The largest island is Sand Island, which has housing and an airstrip. Immediately to the east of Sand Island across the narrow Brooks Channel is Eastern Island, which is uninhabited and no longer has any facilities. Forming a rough, incomplete circle around the two main islands and creating Midway Lagoon is Spit Island, a narrow reef.

Palmyra Atoll

Palmyra Atoll

Palmyra Atoll, also referred to as Palmyra Island, is one of the Northern Line Islands. It is located almost due south of the Hawaiian Islands, roughly one-third of the way between Hawaii and American Samoa. North America is about 3,300 miles northeast and New Zealand the same distance southwest, placing the atoll at the approximate center of the Pacific Ocean. The land area is 4.6 sq mi (12 km2), with about 9 miles (14 km) of sea-facing coastline and reef. There is one boat anchorage known as West Lagoon, accessible from the sea by a narrow artificial channel.

French Polynesia

French Polynesia

French Polynesia is an overseas collectivity of France and its sole overseas country. It comprises 121 geographically dispersed islands and atolls stretching over more than 2,000 kilometres (1,200 mi) in the South Pacific Ocean. The total land area of French Polynesia is 3,521 square kilometres (1,359 sq mi), with a population of 278,786.

Johnston Atoll

Johnston Atoll

Johnston Atoll is an unincorporated territory of the United States, currently administered by the United States Fish and Wildlife Service (USFWS). Johnston Atoll is a National Wildlife Refuge and part of the Pacific Remote Islands Marine National Monument. It is closed to public entry, and limited access for management needs is only granted by Letter of Authorization from the United States Air Force and a Special Use Permit from the U.S. Fish and Wildlife Service.

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.[5]

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

Plaque commemorating the Railway General Time Convention of 1883 in North America
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
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 Great Western Railway started using GMT kept by portable chronometers.[6] 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.[7]

On November 2, 1868, the then British Colony of New Zealand officially adopted a standard time to be observed throughout the colony.[8] 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.[9]

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.[10]

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

Charles F. Dowd proposed a system of hourly standard time zones for North American railroads around 1863, 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. Instead, U.S. and Canadian railroads implemented a version proposed by William F. Allen, the editor of the Traveler's Official Railway Guide.[11] 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",[12] 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.[13] 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

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.[14][15]

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.[16] 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.[17]

World map of time zones in 1928
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.[18]

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.[19] In Russia, which has 11 time zones, two time zones were removed in 2010[20][21] and reinstated in 2014.[22]

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Earth

Earth

Earth is the third planet from the Sun and the only place known in the universe where life has originated and found habitability. While Earth may not contain the largest volumes of water in the Solar System, only Earth sustains liquid surface water, extending over 70.8% of the Earth with its ocean, making Earth an ocean world. Earth's polar regions currently retain most of all other water with large sheets of ice covering ocean and land, dwarfing Earth's groundwater, lakes, rivers and atmospheric water. Land, consisting of continents and islands, extends over 29.2% of the Earth and is widely covered by vegetation. Below Earth's surface material lies Earth's crust consisting of several slowly moving tectonic plates, which interact to produce mountain ranges, volcanoes, and earthquakes. Earth's liquid outer core generates a magnetic field that shapes the magnetosphere of Earth, largely deflecting destructive solar winds and cosmic radiation.

Degree (angle)

Degree (angle)

A degree, usually denoted by °, is a measurement of a plane angle in which one full rotation is 360 degrees.

Longitude

Longitude

Longitude is a geographic coordinate that specifies the east–west position of a point on the surface of the Earth, or another celestial body. It is an angular measurement, usually expressed in degrees and denoted by the Greek letter lambda (λ). Meridians are semicircular lines running from pole to pole that connect points with the same longitude. The prime meridian defines 0° longitude; by convention the International Reference Meridian for the Earth passes near the Royal Observatory in Greenwich, England on the island of Great Britain. Positive longitudes are east of the prime meridian, and negative ones are west.

London

London

London is the capital and largest city of England and the United Kingdom, with a population of just under 9 million. It stands on the River Thames in south-east England at the head of a 50-mile (80 km) estuary down to the North Sea, and has been a major settlement for two millennia. The City of London, its ancient core and financial centre, was founded by the Romans as Londinium and retains its medieval boundaries. The City of Westminster, to the west of the City of London, has for centuries hosted the national government and parliament. Since the 19th century, the name "London" has also referred to the metropolis around this core, historically split between the counties of Middlesex, Essex, Surrey, Kent, and Hertfordshire, which since 1965 has largely comprised Greater London, which is governed by 33 local authorities and the Greater London Authority.

Bristol

Bristol

Bristol is a city, ceremonial county and unitary authority in England. Situated on the River Avon, it is bordered by the ceremonial counties of Gloucestershire to the north and Somerset to the south. Bristol is the most populous city in South West England. The wider Bristol Built-up Area is the eleventh most populous urban area in the United Kingdom.

Greenwich Mean Time

Greenwich Mean Time

Greenwich Mean Time (GMT) is the mean solar time at the Royal Observatory in Greenwich, London, counted from midnight. At different times in the past, it has been calculated in different ways, including being calculated from noon; as a consequence, it cannot be used to specify a particular time unless a context is given. The term 'GMT' is also used as one of the names for the time zone UTC+00:00 and, in UK law, is the basis for civil time in the United Kingdom.

England

England

England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea area of the Atlantic Ocean to the southwest. It is separated from continental Europe by the North Sea to the east and the English Channel to the south. The country covers five-eighths of the island of Great Britain, which lies in the North Atlantic, and includes over 100 smaller islands, such as the Isles of Scilly and the Isle of Wight.

Coventry Transport Museum

Coventry Transport Museum

Coventry Transport Museum is a transport museum, located in Coventry city centre, England.

Great Western Railway

Great Western Railway

The Great Western Railway (GWR) was a British railway company that linked London with the southwest, west and West Midlands of England and most of Wales. It was founded in 1833, received its enabling Act of Parliament on 31 August 1835 and ran its first trains in 1838 with the initial route completed between London and Bristol in 1841. It was engineered by Isambard Kingdom Brunel, who chose a broad gauge of 7 ft —later slightly widened to 7 ft 1⁄4 in —but, from 1854, a series of amalgamations saw it also operate 4 ft 8+1⁄2 in standard-gauge trains; the last broad-gauge services were operated in 1892.

Marine chronometer

Marine chronometer

A marine chronometer is a precision timepiece that is carried on a ship and employed in the determination of the ship's position by celestial navigation. It is used to determine longitude by comparing Greenwich Mean Time (GMT), and the time at the current location found from observations of celestial bodies. When first developed in the 18th century, it was a major technical achievement, as accurate knowledge of the time over a long sea voyage was vital for effective navigation, lacking electronic or communications aids. The first true chronometer was the life work of one man, John Harrison, spanning 31 years of persistent experimentation and testing that revolutionized naval navigation and enabling the Age of Discovery and colonialism to accelerate.

History of rail transport in Great Britain

History of rail transport in Great Britain

The railway system of Great Britain started with the building of local isolated wooden wagonways starting in the 1560s. A patchwork of local rail links operated by small private railway companies developed in the late 18th century. These isolated links expanded during the railway boom of the 1840s into a national network, although still run by dozens of competing companies. Over the course of the 19th and early 20th centuries, these amalgamated or were bought by competitors until only a handful of larger companies remained. The entire network was brought under government control during the First World War and a number of advantages of amalgamation and planning were demonstrated. However, the government resisted calls for the nationalisation of the network. In 1923, almost all the remaining companies were grouped into the "Big Four": the Great Western Railway, the London and North Eastern Railway, the London, Midland and Scottish Railway and the Southern Railway. The "Big Four" were joint-stock public companies and they continued to run the railway system until 31 December 1947.

Colony of New Zealand

Colony of New Zealand

The Colony of New Zealand was a colony of the United Kingdom of Great Britain and Ireland that encompassed the islands of New Zealand from 1841 to 1907. The power of the British Government was vested in the governor of New Zealand. The colony had three capitals: Okiato in 1841; Auckland from 1841 to 1865; and Wellington, which was the capital until the colony's reorganisation into a Dominion, and continues to be the capital of New Zealand to the present day.

Notation

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.[23]

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".[24] UTC time is also known as "Zulu" time, since "Zulu" is a phonetic alphabet code word for the letter "Z".[24]

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).[25]

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).[26]

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ISO 8601

ISO 8601

ISO 8601 is an international standard covering the worldwide exchange and communication of date and time-related data. It is maintained by the Geneva-based International Organization for Standardization (ISO) and was first published in 1988, with updates in 1991, 2000, 2004, and 2019, and an amendment in 2022. The standard provides a well-defined, unambiguous method of representing calendar dates and times in worldwide communications, especially to avoid misinterpreting numeric dates and times when such data is transferred between countries with different conventions for writing numeric dates and times.

International Organization for Standardization

International Organization for Standardization

The International Organization for Standardization is an international standard development organization composed of representatives from the national standards organizations of member countries. Membership requirements are given in Article 3 of the ISO Statutes.

Coordinated Universal Time

Coordinated Universal Time

Coordinated Universal Time or UTC is the primary time standard by which the world regulates clocks and time. It is within about one second of mean solar time at 0° longitude and is not adjusted for daylight saving time. It is effectively a successor to Greenwich Mean Time (GMT).

UTC offset

UTC offset

The UTC offset is the difference in hours and minutes between Coordinated Universal Time (UTC) and local solar time, at a particular place. This difference is expressed with respect to UTC and is generally shown in the format ±[hh]:[mm], ±[hh][mm], or ±[hh]. So if the time being described is two hours ahead of UTC, the UTC offset would be "+02:00", "+0200", or simply "+02".

Germany

Germany

Germany, officially the Federal Republic of Germany, is a country in Central Europe. It is the second-most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated between the Baltic and North seas to the north, and the Alps to the south; it covers an area of 357,022 square kilometres (137,847 sq mi), with a population of around 84 million within its 16 constituent states. Germany borders Denmark to the north, Poland and the Czech Republic to the east, Austria and Switzerland to the south, and France, Luxembourg, Belgium, and the Netherlands to the west. The nation's capital and most populous city is Berlin and its main financial centre is Frankfurt; the largest urban area is the Ruhr.

UTC+01:00

UTC+01:00

UTC+01:00 is an identifier for a time offset from UTC of +01:00. In ISO 8601, the associated time would be written as 2019-02-07T23:28:34+01:00. This time is used in:Central European Time West Africa Time Western European Summer Time British Summer Time Irish Standard Time

Daylight saving time

Daylight saving time

Daylight saving time (DST), also referred to as daylight savings time, daylight time, or summer time, is the practice of advancing clocks during warmer months so that darkness falls at a later clock time. The typical implementation of DST is to set clocks forward by one hour in either the late winter or spring, and to set clocks back by one hour in the fall to return to standard time. As a result, there is one 23-hour day in early spring and one 25-hour day in the middle of autumn.

Chicago

Chicago

Chicago is the most populous city in the U.S. state of Illinois and the third most populous in the United States after New York City and Los Angeles. With a population of 2,746,388 in the 2020 census, it is also the most populous city in the Midwest. As the seat of Cook County, the city is the center of the Chicago metropolitan area, one of the largest in the world.

UTC−06:00

UTC−06:00

UTC−06:00 is an identifier for a time offset from UTC of −06:00. In North America, it is observed in the Central Time Zone during standard time, and in the Mountain Time Zone during the other eight months. Several Latin American countries and a few other places use it year-round.

UTC−05:00

UTC−05:00

UTC−05:00 is an identifier for a time offset from UTC of −05:00. In North America, it is observed in the Eastern Time Zone during standard time, and in the Central Time Zone during the other eight months. The western Caribbean uses it year round.

List of time zone abbreviations

List of time zone abbreviations

This is a list of time zone abbreviations.

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.

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New York Stock Exchange

New York Stock Exchange

The New York Stock Exchange is an American stock exchange in the Financial District of Lower Manhattan in New York City. It is by far the world's largest stock exchange by market capitalization. The NYSE trading floor is at the New York Stock Exchange Building on 11 Wall Street and 18 Broad Street and is a National Historic Landmark. An additional trading room, at 30 Broad Street, was closed in February 2007.

California

California

California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2 million residents across a total area of approximately 163,696 square miles (423,970 km2), it is the most populous U.S. state and the third-largest by area. It is also the most populated subnational entity in North America and the 34th most populous in the world. The Greater Los Angeles and San Francisco Bay areas are the nation's second and fifth most populous urban regions respectively, with the former having more than 18.7 million residents and the latter having over 9.6 million. Sacramento is the state's capital, while Los Angeles is the most populous city in the state and the second most populous city in the country. San Francisco is the second most densely populated major city in the country. Los Angeles County is the country's most populous, while San Bernardino County is the largest county by area in the country. California borders Oregon to the north, Nevada and Arizona to the east, the Mexican state of Baja California to the south; and it has a coastline along the Pacific Ocean to the west.

India

India

India, officially the Republic of India, is a country in South Asia. It is the seventh-largest country by area and the second-most populous country. Bounded by the Indian Ocean on the south, the Arabian Sea on the southwest, and the Bay of Bengal on the southeast, it shares land borders with Pakistan to the west; China, Nepal, and Bhutan to the north; and Bangladesh and Myanmar to the east. In the Indian Ocean, India is in the vicinity of Sri Lanka and the Maldives; its Andaman and Nicobar Islands share a maritime border with Thailand, Myanmar, and Indonesia.

Egypt

Egypt

Egypt, officially the Arab Republic of Egypt, is a transcontinental country spanning the northeast corner of Africa and southwest corner of Asia via a land bridge formed by the Sinai Peninsula. It is bordered by the Mediterranean Sea to the north, the Gaza Strip of Palestine and Israel to the northeast, the Red Sea to the east, Sudan to the south, and Libya to the west. The Gulf of Aqaba in the northeast separates Egypt from Jordan and Saudi Arabia. Cairo is the capital and largest city of Egypt, while Alexandria, the second-largest city, is an important industrial and tourist hub at the Mediterranean coast. At approximately 100 million inhabitants, Egypt is the 14th-most populated country in the world.

Pakistan

Pakistan

Pakistan, officially the Islamic Republic of Pakistan, is a country in South Asia. It is the world's fifth-most populous country, with a population of almost 243 million people, and has the world's second-largest Muslim population just behind Indonesia. Pakistan is the 33rd-largest country in the world by area and the second-largest in South Asia, spanning 881,913 square kilometres. It has a 1,046-kilometre (650-mile) coastline along the Arabian Sea and Gulf of Oman in the south, and is bordered by India to the east, Afghanistan to the west, Iran to the southwest, and China to the northeast. It is separated narrowly from Tajikistan by Afghanistan's Wakhan Corridor in the north, and also shares a maritime border with Oman. Islamabad is the nation's capital, while Karachi is its largest city and financial centre.

UTC−09:00

UTC−09:00

UTC−09:00 is an identifier for a time offset from UTC of −09:00. This time is used in:

UTC−08:00

UTC−08:00

UTC−08:00 is an identifier for a time offset from UTC of −08:00. This time is used:

UTC−07:00

UTC−07:00

UTC−07:00 is an identifier for a time offset from UTC of −07:00. In North America, it is observed in the Mountain Time Zone during standard time, and in the Pacific Time Zone during the other eight months. Some locations use it year-round.

UTC−06:00

UTC−06:00

UTC−06:00 is an identifier for a time offset from UTC of −06:00. In North America, it is observed in the Central Time Zone during standard time, and in the Mountain Time Zone during the other eight months. Several Latin American countries and a few other places use it year-round.

UTC−05:00

UTC−05:00

UTC−05:00 is an identifier for a time offset from UTC of −05:00. In North America, it is observed in the Eastern Time Zone during standard time, and in the Central Time Zone during the other eight months. The western Caribbean uses it year round.

UTC−04:00

UTC−04:00

UTC−04:00 is an identifier for a time offset from UTC of −04:00.

UTC−03:30

UTC−03:30

UTC−03:30 is an identifier for a time offset from UTC of −03:30. It is used in the Canadian province of Newfoundland and Labrador as Newfoundland Time Zone.

Nautical time zones

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.[27][28][29]

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.[30] Some ships simply remain on the time of the departing port during the whole trip.[31]

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
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
.mw-parser-output .legend{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .legend-color{display:inline-block;min-width:1.25em;height:1.25em;line-height:1.25;margin:1px 0;text-align:center;border:1px solid black;background-color:transparent;color:black}.mw-parser-output .legend-text{}  DST observed   DST formerly observed   DST never observed
  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 located 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.[32] 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.[33] 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.[34] 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.[35]

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.[36] 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.[37]

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.[38] 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.
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.

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France

France

France, officially the French Republic, is a country located primarily in Western Europe. It also includes overseas regions and territories in the Americas and the Atlantic, Pacific and Indian Oceans, giving it one of the largest discontiguous exclusive economic zones in the world. Its metropolitan area extends from the Rhine to the Atlantic Ocean and from the Mediterranean Sea to the English Channel and the North Sea; overseas territories include French Guiana in South America, Saint Pierre and Miquelon in the North Atlantic, the French West Indies, and many islands in Oceania and the Indian Ocean. Its eighteen integral regions span a combined area of 643,801 km2 (248,573 sq mi) and had a total population of over 68 million as of January 2023. France is a unitary semi-presidential republic with its capital in Paris, the country's largest city and main cultural and commercial centre; other major urban areas include Marseille, Lyon, Toulouse, Lille, Bordeaux, and Nice.

Central European Time

Central European Time

Central European Time (CET) is a standard time of Central- and parts of Western Europe which is 1 hour ahead of Coordinated Universal Time (UTC). The time offset from UTC can be written as UTC+01:00. It is used in most parts of Europe and in a few North African countries. CET is also known as Middle European Time and by colloquial names such as Amsterdam Time, Berlin Time, Brussels Time, Madrid Time, Paris Time, Rome Time, Warsaw Time or even Romance Standard Time (RST).

Daylight saving time

Daylight saving time

Daylight saving time (DST), also referred to as daylight savings time, daylight time, or summer time, is the practice of advancing clocks during warmer months so that darkness falls at a later clock time. The typical implementation of DST is to set clocks forward by one hour in either the late winter or spring, and to set clocks back by one hour in the fall to return to standard time. As a result, there is one 23-hour day in early spring and one 25-hour day in the middle of autumn.

Nome, Alaska

Nome, Alaska

Nome is a city in the Nome Census Area in the Unorganized Borough of Alaska, United States. The city is located on the southern Seward Peninsula coast on Norton Sound of the Bering Sea. It had a population of 3,699 recorded in the 2020 census, up from 3,598 in 2010. Nome was incorporated on April 9, 1901, and was once the most-populous city in Alaska. Nome lies within the region of the Bering Straits Native Corporation, which is headquartered in Nome.

Samoa Time Zone

Samoa Time Zone

The Samoa Time Zone or Samoa Standard Time (SST) observes standard time by subtracting eleven hours from Coordinated Universal Time (UTC-11:00). The clock time in this zone is based on the mean solar time of the 165th meridian west of the Greenwich Observatory.

165th meridian west

165th meridian west

The meridian 165° west of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, North America, the Pacific Ocean, the Southern Ocean, and Antarctica to the South Pole.

Alaska Time Zone

Alaska Time Zone

The Alaska Time Zone observes standard time by subtracting nine hours from Coordinated Universal Time (UTC−09:00). During daylight saving time its time offset is eight hours (UTC−08:00). The clock time in this zone is based on mean solar time at the 135th meridian west of the Greenwich Observatory.

135th meridian west

135th meridian west

The meridian 135° west of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, North America, the Pacific Ocean, the Southern Ocean, and Antarctica to the South Pole.

Kotzebue, Alaska

Kotzebue, Alaska

Kotzebue or Qikiqtaġruk is a city in the Northwest Arctic Borough in the U.S. state of Alaska. It is the borough's seat, by far its largest community and the economic and transportation hub of the subregion of Alaska encompassing the borough. The population of the city was 3,102 as of the 2020 census, down from 3,201 in 2010. The city has received an All-America City award.

China

China

China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and borders fourteen countries by land, the most of any country in the world, tied with Russia. With an area of approximately 9.6 million square kilometres (3,700,000 sq mi), it is the world's third largest country by total land area. The country consists of 22 provinces, five autonomous regions, four municipalities, and two special administrative regions. The national capital is Beijing, and the most populous city and largest financial center is Shanghai.

List of extreme points of China

List of extreme points of China

This is a list of the extreme points of China, compared both globally and within the country.

120th meridian east

120th meridian east

The meridian 120° east of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, Asia, the Indian Ocean, Australia, the Southern Ocean, and Antarctica to the South Pole. In mean solar time this offset is the UTC+08:00 time zone.

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.

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Daylight saving time

Daylight saving time

Daylight saving time (DST), also referred to as daylight savings time, daylight time, or summer time, is the practice of advancing clocks during warmer months so that darkness falls at a later clock time. The typical implementation of DST is to set clocks forward by one hour in either the late winter or spring, and to set clocks back by one hour in the fall to return to standard time. As a result, there is one 23-hour day in early spring and one 25-hour day in the middle of autumn.

Clock

Clock

A clock or a timepiece is a device used to measure and indicate time. The clock is one of the oldest human inventions, meeting the need to measure intervals of time shorter than the natural units such as the day, the lunar month and the year. Devices operating on several physical processes have been used over the millennia.

Hour

Hour

An hour is a unit of time historically reckoned as 1⁄24 of a day and defined contemporarily as exactly 3,600 seconds (SI). There are 60 minutes in an hour, and 24 hours in a day.

Spring (season)

Spring (season)

Spring, also known as springtime, is one of the four temperate seasons, succeeding winter and preceding summer. There are various technical definitions of spring, but local usage of the term varies according to local climate, cultures and customs. When it is spring in the Northern Hemisphere, it is autumn in the Southern Hemisphere and vice versa. At the spring equinox, days and nights are approximately twelve hours long, with daytime length increasing and nighttime length decreasing as the season progresses until the Summer Solstice in June and December.

Autumn

Autumn

Autumn, also known as fall in American English and Canadian English, is one of the four temperate seasons on Earth. Outside the tropics, autumn marks the transition from summer to winter, in September or March. Autumn is the season when the duration of daylight becomes noticeably shorter and the temperature cools considerably. Day length decreases and night length increases as the season progresses until the Winter Solstice in December and June. One of its main features in temperate climates is the striking change in colour for the leaves of deciduous trees as they prepare to shed.

World War I

World War I

World War I or the First World War, often abbreviated as WWI, was one of the deadliest global conflicts in history. It was fought between two coalitions, the Allies and the Central Powers. Fighting occurred throughout Europe, the Middle East, Africa, the Pacific, and parts of Asia. An estimated 9 million soldiers were killed in combat, plus another 23 million wounded, while 5 million civilians died as a result of military action, hunger, and disease. Millions more died as a result of genocide, while the 1918 Spanish flu pandemic was exacerbated by the movement of combatants during the war.

Energy conservation

Energy conservation

Energy conservation is the effort to reduce wasteful energy consumption by using fewer energy services. This can be done by using energy more effectively or changing one's behavior to use less service. Energy conservation can be achieved through efficient energy use, which has a number of advantages, including a reduction in greenhouse gas emissions and a smaller carbon footprint, as well as cost, water, and energy savings.

Daylight saving time by country

Daylight saving time by country

Daylight saving time (DST), also known as summer time, is the practice of advancing clocks during part of the year, typically by one hour around spring and summer, so that daylight ends at a later time of the day. As of 2023, DST is observed in most of Europe, most of North America and parts of Africa and Asia around the Northern Hemisphere summer, and in parts of South America and Oceania around the Southern Hemisphere summer. It was also formerly observed in other areas.

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,[39] whereas the US version shows Eastern Time.[40] 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.)[41] 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.[42] 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,[43] although normal daylight saving start and end are compensated for (similar to much other calendar software).

Operating systems

Unix

Most Unix-like systems, including Linux and Mac OS X, keep system time in time_t 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.[44] By default the external representation is as UTC (Coordinated Universal Time), though individual processes can specify time zones using the TZ environment variable.[45] This allows users in multiple time zones to use the same computer, with their respective local times displayed correctly to each user. Time zone information most commonly comes from the IANA time zone database. In fact, many systems, including anything using the GNU C Library, can make use of this database.

Microsoft Windows

Windows-based computer systems prior to Windows 2000 used local time, but Windows 2000 and later can use UTC as the basic system time.[46] 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 information, the Java Platform, from version 1.3.1, has maintained its own time zone database. This database is updated whenever time zone rules change. Oracle provides an updater tool for this purpose.[47]

As an alternative to the time zone information bundled with the Java Platform, programmers may choose to use the Joda-Time library.[48] This library includes its own time zone data based on the IANA time zone database.[49]

As of Java 8 there is a new date and time API that can help with converting time zones. Java 8 Date Time

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.[50] However, due to size constraint, some implementations or distributions do not include it.[51]

Perl

The DateTime object in Perl supports all time zones in the Olson DB and includes the ability to get, set and convert between time zones.[52]

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.[53] 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.[54] 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.[55]

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.[56]

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Operating system

Operating system

An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs.

Coordinated Universal Time

Coordinated Universal Time

Coordinated Universal Time or UTC is the primary time standard by which the world regulates clocks and time. It is within about one second of mean solar time at 0° longitude and is not adjusted for daylight saving time. It is effectively a successor to Greenwich Mean Time (GMT).

Eastern Time Zone

Eastern Time Zone

The Eastern Time Zone (ET) is a time zone encompassing part or all of 23 states in the eastern part of the United States, parts of eastern Canada, the state of Quintana Roo in Mexico, Panama, Colombia, mainland Ecuador, Peru, and a small portion of westernmost Brazil in South America, along with certain Caribbean and Atlantic islands.

Pacific Time Zone

Pacific Time Zone

The Pacific Time Zone (PT) is a time zone encompassing parts of western Canada, the western United States, and western Mexico. Places in this zone observe standard time by subtracting eight hours from Coordinated Universal Time (UTC−08:00). During daylight saving time, a time offset of UTC−07:00 is used.

Email

Email

Electronic mail is a method of transmitting and receiving messages using electronic devices. It was conceived in the late–20th century as the digital version of, or counterpart to, mail. Email is a ubiquitous and very widely used communication medium; in current use, an email address is often treated as a basic and necessary part of many processes in business, commerce, government, education, entertainment, and other spheres of daily life in most countries.

Internet Relay Chat

Internet Relay Chat

Internet Relay Chat (IRC) is a text-based chat system for instant messaging. IRC is designed for group communication in discussion forums, called channels, but also allows one-on-one communication via private messages as well as chat and data transfer, including file sharing.

Database

Database

In computing, a database is an organized collection of data stored and accessed electronically. Small databases can be stored on a file system, while large databases are hosted on computer clusters or cloud storage. The design of databases spans formal techniques and practical considerations, including data modeling, efficient data representation and storage, query languages, security and privacy of sensitive data, and distributed computing issues, including supporting concurrent access and fault tolerance.

Microsoft Outlook

Microsoft Outlook

Microsoft Outlook is a personal information manager software system from Microsoft, available as a part of the Microsoft Office and Microsoft 365 software suites. Though primarily an email client, Outlook also includes such functions as calendaring, task managing, contact managing, note-taking, journal logging and web browsing, and has also become a popular email client for many businesses.

Daylight saving time

Daylight saving time

Daylight saving time (DST), also referred to as daylight savings time, daylight time, or summer time, is the practice of advancing clocks during warmer months so that darkness falls at a later clock time. The typical implementation of DST is to set clocks forward by one hour in either the late winter or spring, and to set clocks back by one hour in the fall to return to standard time. As a result, there is one 23-hour day in early spring and one 25-hour day in the middle of autumn.

Google Calendar

Google Calendar

Google Calendar is a time-management and scheduling calendar service developed by Google. It became available in beta release April 13, 2006, and in general release in July 2009, on the web and as mobile apps for the Android and iOS platforms.

Linux

Linux

Linux is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, which includes the kernel and supporting system software and libraries, many of which are provided by the GNU Project. Many Linux distributions use the word "Linux" in their name, but the Free Software Foundation uses the name "GNU/Linux" to emphasize the importance of GNU software, causing some controversy.

Leap second

Leap second

A leap second is a one-second adjustment that is occasionally applied to Coordinated Universal Time (UTC), to accommodate the difference between precise time and imprecise observed solar time (UT1), which varies due to irregularities and long-term slowdown in the Earth's rotation. The UTC time standard, widely used for international timekeeping and as the reference for civil time in most countries, uses TAI and consequently would run ahead of observed solar time unless it is reset to UT1 as needed. The leap second facility exists to provide this adjustment. The leap second was introduced in 1972 and since then 27 leap seconds have been added to UTC.

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).[57][58]

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.[59]

Discover more about Time in outer space related topics

Space exploration

Space exploration

Space exploration is the use of astronomy and space technology to explore outer space. While the exploration of space is carried out mainly by astronomers with telescopes, its physical exploration is conducted both by uncrewed robotic space probes and human spaceflight. Space exploration, like its classical form astronomy, is one of the main sources for space science.

International Space Station

International Space Station

The International Space Station (ISS) is the largest modular space station in low Earth orbit. The project involves five space agencies: the United States' NASA, Russia's Roscosmos, Japan's JAXA, Europe's ESA, and Canada's CSA. The ownership and use of the space station is established by intergovernmental treaties and agreements. The station serves as a microgravity and space environment research laboratory in which scientific research is conducted in astrobiology, astronomy, meteorology, physics, and other fields. The ISS is suited for testing the spacecraft systems and equipment required for possible future long-duration missions to the Moon and Mars.

Timekeeping on Mars

Timekeeping on Mars

Though no standard exists, numerous calendars and other timekeeping approaches have been proposed for the planet Mars. The most commonly seen in the scientific literature denotes the time of year as the number of degrees on its orbit from the northern vernal equinox, and increasingly there is use of numbering the Martian years beginning at the equinox that occurred April 11, 1955.

Source: "Time zone", Wikipedia, Wikimedia Foundation, (2023, February 15th), https://en.wikipedia.org/wiki/Time_zone.

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See also
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Further reading
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