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Standard time is the synchronization of clocks within a geographical region to a single time standard, rather than a
local mean time Local mean time (LMT) is a form of solar time that corrects the variations of local apparent time, forming a uniform time scale at a specific longitude. This measurement of time was used for everyday use during the 19th century before time zones ...
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 Weather forecasting or weather prediction is the application of science and technology forecasting, to predict the conditions of the Earth's atmosphere, atmosphere for a given location and time. People have attempted to predict the weather info ...
and train travel. Applied globally in the 20th century, the geographical regions became
time zone A time zone is an area which observes a uniform standard time for legal, Commerce, commercial and social purposes. Time zones tend to follow the boundaries between Country, countries and their Administrative division, subdivisions instead of ...
s. 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 Daylight saving time (DST), also referred to as daylight savings time, daylight time (Daylight saving time in the United States, United States and Daylight saving time in Canada, Canada), or summer time (British Summer Time, United Kingdom, ...
. The adoption of standard time, because of the inseparable correspondence between
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 lett ...
and time, solidified the concept of halving the globe into the Eastern Hemisphere and the
Western Hemisphere The Western Hemisphere is the half of the planet Earth that lies west of the Prime Meridian (which crosses Greenwich, London, United Kingdom) and east of the 180th meridian.- The other half is called the Eastern Hemisphere. Geopolitically, ...
, with one
Prime Meridian A prime meridian is an arbitrarily chosen meridian (geography), meridian (a line of longitude) in a geographic coordinate system at which longitude is defined to be 0°. On a spheroid, a prime meridian and its anti-meridian (the 180th meridian ...
replacing the various prime meridians that had previously been used.


History of standard time

During the 19th century, scheduled steamships and trains required time standardisation in the industrialized world.


Great Britain

A standardised time system was first used by British railways on 1 December 1847, when they switched from local mean time, which varied from place to place, to
Greenwich Mean Time Greenwich Mean Time (GMT) is the local mean time at the Royal Observatory, Greenwich, Royal Observatory in Greenwich, London, counted from midnight. At different times in the past, it has been calculated in different ways, including being ...
(GMT). It was also given the name railway time, reflecting the important role the railway companies played in bringing it about. The vast majority of Great Britain's public clocks were standardised to GMT by 1855.


North America

Until 1883, each United States railroad chose its own time standards. The Pennsylvania Railroad used the "Allegheny Time" system, an astronomical timekeeping service which had been developed by Samuel Pierpont Langley at the
University of Pittsburgh The University of Pittsburgh (Pitt) is a Commonwealth System of Higher Education, state-related research university in Pittsburgh, Pennsylvania, United States. The university is composed of seventeen undergraduate and graduate schools and colle ...
's Allegheny Observatory (then known as the Western University of Pennsylvania, located in
Pittsburgh, Pennsylvania Pittsburgh ( ) is a city in Allegheny County, Pennsylvania, United States, and its county seat. It is the List of municipalities in Pennsylvania#Municipalities, second-most populous city in Pennsylvania (after Philadelphia) and the List of Un ...
). Instituted in 1869, the Allegheny Observatory's service is believed to have been the first regular and systematic system of time distribution to railroads and cities as well as the origin of the modern standard time system. By 1870 the Allegheny Time service extended over 2,500 miles with 300 telegraph offices receiving time signals. However, almost all railroads out of New York ran on New York time, and railroads west from Chicago mostly used Chicago time, but between Chicago and Pittsburgh/Buffalo the norm was Columbus time, even on railroads such as the PFtW&C and LS&MS, which did not run through Columbus. The Santa Fe Railroad used Jefferson City (Missouri) time all the way to its west end at Deming, New Mexico, as did the east–west lines across Texas; Central Pacific and Southern Pacific Railroads used San Francisco time all the way to El Paso. The Northern Pacific Railroad had seven time zones between St. Paul and the 1883 west end of the railroad at Wallula Jct; the Union Pacific Railway was at the other extreme, with only two time zones between
Omaha Omaha ( ) is the List of cities in Nebraska, most populous city in the U.S. state of Nebraska. It is located in the Midwestern United States along the Missouri River, about north of the mouth of the Platte River. The nation's List of United S ...
and Ogden. In 1870, Charles F. Dowd proposed four time zones based on the meridian through
Washington, DC Washington, D.C., formally the District of Columbia and commonly known as Washington or D.C., is the capital city and Federal district of the United States, federal district of the United States. The city is on the Potomac River, across from ...
, for North American railroads. In 1872 he revised his proposal to base it on the Greenwich meridian.
Sandford Fleming Sir Sandford Fleming (January 7, 1827 – July 22, 1915) was a Scottish Canadian engineer and inventor. Born and raised in Scotland, he immigrated to colonial Canada at the age of 18. He promoted worldwide standard time zones, a prime meridian, ...
, a Scottish-born Canadian engineer, proposed worldwide Standard Time at a meeting of the Royal Canadian Institute on February 8, 1879. Cleveland Abbe advocated standard time to better coordinate international weather observations and resultant
weather forecasts Weather is the state of the atmosphere, describing for example the degree to which it is hot or cold, wet or dry, calm or stormy, clear or cloud cover, cloudy. On Earth, most weather phenomena occur in the lowest layer of the planet's atmo ...
, which had been coordinated using local
solar time Solar time is a calculation of the passage of time based on the position of the Sun in the sky. The fundamental unit of solar time is the day, based on the synodic rotation period. Traditionally, there are three types of time reckoning based ...
. In 1879 he recommended four time zones across the
contiguous United States The contiguous United States, also known as the U.S. mainland, officially referred to as the conterminous United States, consists of the 48 adjoining U.S. states and the District of Columbia of the United States in central North America. The te ...
, based upon
Greenwich Mean Time Greenwich Mean Time (GMT) is the local mean time at the Royal Observatory, Greenwich, Royal Observatory in Greenwich, London, counted from midnight. At different times in the past, it has been calculated in different ways, including being ...
. The General Time Convention (renamed the American Railway Association in 1891), an organization of US railroads charged with coordinating schedules and operating standards, became increasingly concerned that if the US government adopted a standard time scheme it would be disadvantageous to its member railroads. William F. Allen, the Convention secretary, argued that North American railroads should adopt a five-zone standard, similar to the one in use today, to avoid government action. On October 11, 1883, the heads of the major railroads met in
Chicago Chicago is the List of municipalities in Illinois, most populous city in the U.S. state of Illinois and in the Midwestern United States. With a population of 2,746,388, as of the 2020 United States census, 2020 census, it is the List of Unite ...
at the Grand Pacific Hotel and agreed to adopt Allen's proposed system. The members agreed that on Sunday, November 18, 1883, all United States and Canadian railroads would readjust their clocks and watches to reflect the new five-zone system on a telegraph signal from the Allegheny Observatory in Pittsburgh at exactly noon on the 90th meridian.W. F. Allen
"History of the movement by which the adoption of standard time was consummated"
''Proceedings of the American Society'' 4 (1884) 25–50, Appendix 50–89. Hathi Trust Digital Library.
Michael O'Malley, ''Keeping Watch: A History of American Time'' (NY 1990) chapter three Although most railroads adopted the new system as scheduled, some did so early on October 7 and others late on December 2. The
Intercolonial Railway The Intercolonial Railway of Canada , also referred to as the Intercolonial Railway (ICR), was a historic Canada, Canadian railway that operated from 1872 to 1918, when it became part of Canadian National Railways. As the railway was also compl ...
serving the Canadian maritime provinces of
New Brunswick New Brunswick is a Provinces and Territories of Canada, province of Canada, bordering Quebec to the north, Nova Scotia to the east, the Gulf of Saint Lawrence to the northeast, the Bay of Fundy to the southeast, and the U.S. state of Maine to ...
and
Nova Scotia Nova Scotia is a Provinces and territories of Canada, province of Canada, located on its east coast. It is one of the three Maritime Canada, Maritime provinces and Population of Canada by province and territory, most populous province in Atlan ...
just east of
Maine Maine ( ) is a U.S. state, state in the New England region of the United States, and the northeasternmost state in the Contiguous United States. It borders New Hampshire to the west, the Gulf of Maine to the southeast, and the Provinces and ...
decided not to adopt Intercolonial Time based on the 60th meridian west of Greenwich, instead adopting Eastern Time, so only four time zones were actually adopted by American and Canadian railroads in 1883. Major American observatories, including the Allegheny Observatory, the United States Naval Observatory, the
Harvard College Observatory The Harvard College Observatory (HCO) is an institution managing a complex of buildings and multiple instruments used for astronomical research by the Harvard University Department of Astronomy. It is located in Cambridge, Massachusetts, United St ...
, and the Yale University Observatory, agreed to provide telegraphic time signals at noon Eastern Time. Standard time was not enacted into US law until the 1918 Standard Time Act established standard time in time zones; the law also instituted daylight saving time (DST). The daylight saving time portion of the law was repealed in 1919 over a presidential veto, but was re-established nationally during World War II. Congressional Research Service. (2007). "Daylight Saving Time". (Report RS22284)). Originally published by wikileaks. In 2007 the US enacted a federal law formalising the use of
Coordinated Universal Time Coordinated Universal Time (UTC) is the primary time standard globally used to regulate clocks and time. It establishes a reference for the current time, forming the basis for civil time and time zones. UTC facilitates international communicat ...
as the basis of standard time, and the role of the Secretary of Commerce (effectively, the
National Institute of Standards and Technology The National Institute of Standards and Technology (NIST) is an agency of the United States Department of Commerce whose mission is to promote American innovation and industrial competitiveness. NIST's activities are organized into Outline of p ...
) and the
Secretary of the Navy The Secretary of the Navy (SECNAV) is a statutory officer () and the head (chief executive officer) of the Department of the Navy, a military department within the United States Department of Defense. On March 25, 2025, John Phelan was confirm ...
(effectively, the US Naval Observatory) in interpreting standard time. In 1999, standard time was inducted into the North America Railway Hall of Fame in the category "National: Technical Innovations." The
Dominion of Newfoundland Newfoundland was a British dominion in eastern North America, today the modern Canadian province of Newfoundland and Labrador. It included the island of Newfoundland, and Labrador on the continental mainland. Newfoundland was one of the orig ...
, whose capital St. John's falls almost exactly midway between the meridians anchoring the
Atlantic Time Zone The Atlantic Time Zone is a geographical region that keeps standard time—called Atlantic Standard Time (AST)—by subtracting four hours from Coordinated Universal Time ( UTC), resulting in UTC−04:00. AST is observed in parts of North America ...
and the Greenland Time Zone, voted in 1935 to create a half-hour offset time zone known as the Newfoundland Time Zone, at three and a half hours behind Greenwich time.


The Netherlands

In the Netherlands, introduction of the railways made it desirable to create a standard time. On 1 May 1909,
Amsterdam Time UTC+00:20 is an identifier for a UTC offset, time offset from UTC of +00:20. History UTC+00:20 was used in the Netherlands from 1 May 1909 to 16 May 1940. It was known as Amsterdam Time or Dutch Time. The exact time zone was GMT +0h 19m&n ...
or Dutch Time was introduced. Before that, time was measured in different cities; in the east of the country, this was a few minutes earlier than in the west. After that, all parts of the country had the same local time—that of the Wester Tower in
Amsterdam Amsterdam ( , ; ; ) is the capital of the Netherlands, capital and Municipalities of the Netherlands, largest city of the Kingdom of the Netherlands. It has a population of 933,680 in June 2024 within the city proper, 1,457,018 in the City Re ...
(Westertoren/4°53'01.95" E). This time was indicated as GMT +0h 19m 32.13s until 17 March 1937, after which it was simplified to GMT+0h20m. This time zone was also known as the ''Loenen time'' or ''Gorinchem time'', as this was the exact time in both Loenen and Gorinchem. At noon in Amsterdam, it was 11:40 in
London London is the Capital city, capital and List of urban areas in the United Kingdom, largest city of both England and the United Kingdom, with a population of in . London metropolitan area, Its wider metropolitan area is the largest in Wester ...
and 12:40 in
Berlin Berlin ( ; ) is the Capital of Germany, capital and largest city of Germany, by both area and List of cities in Germany by population, population. With 3.7 million inhabitants, it has the List of cities in the European Union by population withi ...
. The shift to the current
Central European Time Central European Time (CET) is a standard time of Central, and parts of Western Europe, which is one hour ahead of Coordinated Universal Time (UTC). The UTC offset, time offset from UTC can be written as UTC+01:00. It is used in most parts of Eur ...
zone took place on 16 May 1940. The German occupiers ordered the clock to be moved an hour and forty minutes forward. This time was kept in summer and winter throughout 1941 and 1942. It was only in November 1942 that a different Winter time was introduced, and the time was adjusted one hour backwards. This lasted for only three years; after the liberation of the Netherlands in 1945, Summer time was abolished for over thirty years, so during those years, standard time was 40 minutes ahead of the original Amsterdam Time. As of 2017, the Netherlands is in line with Central European Time (GMT+1 in the winter, GMT+2 in the summer, which is significantly different from Amsterdam Time).


New Zealand

In September 1868, New Zealand was the first country in the world to establish a nationwide standard time. A
telegraph Telegraphy is the long-distance transmission of messages where the sender uses symbolic codes, known to the recipient, rather than a physical exchange of an object bearing the message. Thus flag semaphore is a method of telegraphy, whereas ...
cable between New Zealand's two main islands became the instigating factor for the establishment of "New Zealand time". In 1868, the Telegraph Department adopted "
Wellington Wellington is the capital city of New Zealand. It is located at the south-western tip of the North Island, between Cook Strait and the Remutaka Range. Wellington is the third-largest city in New Zealand (second largest in the North Island ...
time" as the standard time across all their offices so that opening and closing times could be synchronised. The Post Office, which usually shared the same building, followed suit. However, protests that time was being dictated by one government department, led to a resolution in parliament to establish a standard time for the whole country. The director of the Geological Survey, James Hector, selected New Zealand time to be at the meridian 172°30′E. This was very close to the country's mean
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 lett ...
and exactly 11.5 hours in advance of Greenwich Mean Time. It came into effect on 2 November 1868. For over fifty years, the Colonial Time Service Observatory in Wellington, determined the correct time each morning. At 9 a.m. each day, it was transmitted by
Morse code Morse code is a telecommunications method which Character encoding, encodes Written language, text characters as standardized sequences of two different signal durations, called ''dots'' and ''dashes'', or ''dits'' and ''dahs''. Morse code i ...
to post offices and railway stations around the country. In 1920, radio time signals began broadcasting, greatly increasing the accuracy of the time nationwide.


See also

*
Daylight saving time Daylight saving time (DST), also referred to as daylight savings time, daylight time (Daylight saving time in the United States, United States and Daylight saving time in Canada, Canada), or summer time (British Summer Time, United Kingdom, ...
*
International Meridian Conference The International Meridian Conference was a conference held in October 1884 in Washington, D.C., in the United States, to determine a prime meridian for international use. The conference was held at the request of President of the United State ...
of 1884 * Mecca Time *
Time standard A time standard is a specification for measuring time: either the rate at which time passes or points in time or both. In modern times, several time specifications have been officially recognized as standards, where formerly they were matters of cu ...
*
Time zone A time zone is an area which observes a uniform standard time for legal, Commerce, commercial and social purposes. Time zones tend to follow the boundaries between Country, countries and their Administrative division, subdivisions instead of ...
* Universal Time


References


Further reading

* * * {{Authority control Time scales