A time signal is a visible, audible, mechanical, or electronic
signal
In signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The '' IEEE Transactions on Signal Processing' ...
used as a reference to determine the
time of day
Time is the continued sequence of existence and events that occurs in an apparently irreversible succession from the past, through the present, into the future. It is a component quantity of various measurements used to sequence events, to co ...
.
Church bell
A church bell in Christian architecture is a bell which is rung in a church for a variety of religious purposes, and can be heard outside the building. Traditionally they are used to call worshippers to the church for a communal service, and t ...
s or voices announcing hours of
prayer
Prayer is an invocation or act that seeks to activate a rapport with an object of worship through deliberate communication. In the narrow sense, the term refers to an act of supplication or intercession directed towards a deity or a deified a ...
gave way to automatically operated
chimes on public
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 ...
s; however, audible signals (even signal guns) have limited range. Busy sea
port
A port is a maritime facility comprising one or more wharves or loading areas, where ships load and discharge cargo and passengers. Although usually situated on a sea coast or estuary, ports can also be found far inland, such as Ham ...
s used a visual signal, the dropping of a ball, to allow mariners to check the chronometers used for navigation. The advent of electrical
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 p ...
s allowed widespread and precise distribution of time signals from central observatories.
Railway
Rail transport (also known as train transport) is a means of transport that transfers passengers and goods on wheeled vehicles running on rails, which are incorporated in tracks. In contrast to road transport, where the vehicles run on a pre ...
s were among the first customers for time signals, which allowed synchronization of their operations over wide geographic areas. Dedicated radio time signal stations transmit a signal that allows automatic synchronization of clocks, and commercial broadcasters still include time signals in their programming.
Today, global navigation satellite systems (
GNSS
A satellite navigation or satnav system is a system that uses satellites to provide autonomous geo-spatial positioning. It allows satellite navigation devices to determine their location (longitude, latitude, and altitude/elevation) to high pr ...
) radio signals are used to precisely distribute time signals over much of the world. There are many commercially available
radio controlled clocks available to accurately indicate the local time, both for business and residential use. Computers often set their time from an
Internet atomic clock source. Where this is not available, a locally connected GNSS receiver can precisely set the time using one of several software applications.
Audible and visible time signals
One sort of public time signal is a
striking clock. These clocks are only as good as the clockwork that activates them, but they have improved substantially since the first clocks from the 14th century. Until modern times, a public clock such as
Big Ben
Big Ben is the nickname for the Great Bell of the Great Clock of Westminster, at the north end of the Palace of Westminster in London, England, and the name is frequently extended to refer also to the clock and the clock tower. The officia ...
was the only time standard the general public needed.
Accurate knowledge of time of day is essential for
navigation
Navigation is a field of study that focuses on the process of monitoring and controlling the movement of a craft or vehicle from one place to another.Bowditch, 2003:799. The field of navigation includes four general categories: land navigation, ...
, and ships carried the most accurate
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), or in the modern ...
s available, although they did not keep perfect time. A number of accurate audible or visible time signals were established in many
seaport
A port is a maritime facility comprising one or more wharves or loading areas, where ships load and discharge cargo and passengers. Although usually situated on a sea coast or estuary, ports can also be found far inland, such as Ham ...
cities to enable navigators to set their chronometers.
Signal guns
In
Vancouver
Vancouver ( ) is a major city in western Canada, located in the Lower Mainland region of British Columbia. As the List of cities in British Columbia, most populous city in the province, the 2021 Canadian census recorded 662,248 people in the ...
,
British Columbia
British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, ...
, a "
9 O'Clock Gun" is still shot every night at 9 pm. (This gun was brought to
Stanley Park
Stanley Park is a public park in British Columbia, Canada that makes up the northwestern half of Vancouver's Downtown Peninsula, surrounded by waters of Burrard Inlet and English Bay. The park borders the neighbourhoods of West End and ...
in 1894 by the
Department of Fisheries originally to warn
fishermen
A fisher or fisherman is someone who captures fish and other animals from a body of water, or gathers shellfish.
Worldwide, there are about 38 million commercial and subsistence fishers and fish farmers. Fishers may be professional or recreat ...
of the 6:00 pm Sunday closing of fishing.) The 9:00 pm firing was later established as a time signal for the general population. Until a time gun was installed, the nearby
Brockton Point
Brockton Point is a headland off the Downtown Peninsula of Vancouver, on the north side of Coal Harbour. Named after Francis Brockton, it is the most easterly part of Stanley Park and is home to a 100-year-old lighthouse and several hand-carved ...
lighthouse keeper detonated a stick of dynamite. Elsewhere in Canada, a "Noon Gun" is fired daily from the citadels in
Halifax and
Quebec City
Quebec City ( or ; french: Ville de Québec), officially Québec (), is the capital city of the Provinces and territories of Canada, Canadian province of Quebec. As of July 2021, the city had a population of 549,459, and the Communauté métrop ...
and from
Signal Hill in
St. John's, Newfoundland and Labrador.
In the same manner, a
Noon Gun
The Noon Gun has been a historic time signal in Cape Town, South Africa since 1806. It consists of a pair of black powder Dutch naval guns, fired alternatingly with one serving as a backup. The guns are situated on Signal Hill, close to the ...
has been fired in
Cape Town
Cape Town ( af, Kaapstad; , xh, iKapa) is one of South Africa's three capital cities, serving as the seat of the Parliament of South Africa. It is the legislative capital of the country, the oldest city in the country, and the second largest ...
, South Africa, since 1806. The gun is fired daily from the Lion Battery at
Signal Hill.
The
Noonday Gun
The ''Noonday'' ''Gun'' () is a former naval artillery piece mounted on a small enclosed site near the Causeway Bay Typhoon Shelter on Hong Kong Island, Hong Kong. Owned and operated by Jardine Matheson, the gun is fired every day at noon a ...
serves a similar purpose in
Hong Kong
Hong Kong ( (US) or (UK); , ), officially the Hong Kong Special Administrative Region of the People's Republic of China ( abbr. Hong Kong SAR or HKSAR), is a city and special administrative region of China on the eastern Pearl River Delt ...
. The tradition, which started in the 1860s under British colonial rule, has become a tourist attraction in recent times.
A cannon was fired at one o'clock every weekday at
Liverpool
Liverpool is a city and metropolitan borough in Merseyside, England. With a population of in 2019, it is the 10th largest English district by population and its metropolitan area is the fifth largest in the United Kingdom, with a popul ...
, England, at the
Castle
A castle is a type of fortified structure built during the Middle Ages predominantly by the nobility or royalty and by military orders. Scholars debate the scope of the word ''castle'', but usually consider it to be the private fortified r ...
in
Edinburgh
Edinburgh ( ; gd, Dùn Èideann ) is the capital city of Scotland and one of its 32 Council areas of Scotland, council areas. Historically part of the county of Midlothian (interchangeably Edinburghshire before 1921), it is located in Lothian ...
, Scotland, and also at
Perth
Perth is the capital and largest city of the Australian state of Western Australia. It is the fourth most populous city in Australia and Oceania, with a population of 2.1 million (80% of the state) living in Greater Perth in 2020. Perth is ...
in Australia to establish the time. The Edinburgh "
One O'Clock Gun
Edinburgh Castle is a historic castle in Edinburgh, Scotland. It stands on Castle Rock, which has been occupied by humans since at least the Iron Age, although the nature of the early settlement is unclear. There has been a royal castle on t ...
" is still in operation. A cannon located at the top of Santa Lucia Hill, in
Santiago, Chile
Santiago (, ; ), also known as Santiago de Chile, is the capital (political), capital and largest city of Chile as well as one of the largest cities in the Americas. It is the center of Chile's most densely populated Regions of Chile, region, t ...
, is shot every noon.
In
Rome
, established_title = Founded
, established_date = 753 BC
, founder = King Romulus (legendary)
, image_map = Map of comune of Rome (metropolitan city of Capital Rome, region Lazio, Italy).svg
, map_caption ...
, on the
Janiculum
The Janiculum (; it, Gianicolo ), occasionally the Janiculan Hill, is a hill in western Rome, Italy. Although it is the second-tallest hill (the tallest being Monte Mario) in the contemporary city of Rome, the Janiculum does not figure among th ...
, a hill west of the
Tiber
The Tiber ( ; it, Tevere ; la, Tiberis) is the third-longest List of rivers of Italy, river in Italy and the longest in Central Italy, rising in the Apennine Mountains in Emilia-Romagna and flowing through Tuscany, Umbria, and Lazio, where ...
since 1904 a cannon is fired daily at noon towards the river as a time signal. This was introduced in 1847 by
Pope Pius IX
Pope Pius IX ( it, Pio IX, ''Pio Nono''; born Giovanni Maria Mastai Ferretti; 13 May 1792 – 7 February 1878) was head of the Catholic Church from 1846 to 1878, the longest verified papal reign. He was notable for convoking the First Vatican ...
to synchronise all the church bells of Rome. It was situated in
Castel Sant'Angelo
The Mausoleum of Hadrian, usually known as Castel Sant'Angelo (; English: ''Castle of the Holy Angel''), is a towering cylindrical building in Parco Adriano, Rome, Italy. It was initially commissioned by the Roman Emperor Hadrian as a mausol ...
until 1903 when it was moved to
Monte Mario
Monte Mario (English: Mount Mario or Mount Marius) is the hill that rises in the north-west area of Rome (Italy), on the right bank of the Tiber, crossed by the Via Trionfale. It occupies part of Balduina, of the territory of Municipio Roma I ...
for a few months until it was placed in its current position. The cannon was silenced from the start of
WWII
World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
for about twenty years until 21 April 1959, the 2712th anniversary of Rome's founding, and has been in use since then.
For many years an old cannon was fired "about noon" from a mountain near
Kabul
Kabul (; ps, , ; , ) is the capital and largest city of Afghanistan. Located in the eastern half of the country, it is also a municipality, forming part of the Kabul Province; it is administratively divided into 22 municipal districts. Acco ...
,
Afghanistan
Afghanistan, officially the Islamic Emirate of Afghanistan,; prs, امارت اسلامی افغانستان is a landlocked country located at the crossroads of Central Asia and South Asia. Referred to as the Heart of Asia, it is bordere ...
.
Sirens, whistles, and other audible signals
In many Midwestern US cities where tornadoes are a common hazard, the
emergency sirens are tested regularly at a specified time (say, noon each Saturday); while not primarily intended to mark the time, local people often check their watches when they hear this signal. In many non-seafaring communities, loud factory
whistle
A whistle is an instrument which produces sound from a stream of gas, most commonly air. It may be mouth-operated, or powered by air pressure, steam, or other means. Whistles vary in size from a small slide whistle or nose flute type to a larg ...
s served as public time signals before radio made them obsolete. Sometimes, the tradition of a factory whistle becomes so deeply entrenched in a community that the whistle is maintained long after its original function as a time keeper became obsolete. For example, the
University of Iowa
The University of Iowa (UI, U of I, UIowa, or simply Iowa) is a public university, public research university in Iowa City, Iowa, United States. Founded in 1847, it is the oldest and largest university in the state. The University of Iowa is org ...
's power plant whistle has been reinstated several times by popular demand after numerous attempts to silence it.
Visual signals
In 1861 and 1862, the Edinburgh Post Office Directory published time gun
map
A map is a symbolic depiction emphasizing relationships between elements of some space, such as objects, regions, or themes.
Many maps are static, fixed to paper or some other durable medium, while others are dynamic or interactive. Although ...
s relating the number of seconds required for the report of the time gun to reach various locations in the city. Because
light
Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 tera ...
travels much faster than
sound
In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid.
In human physiology and psychology, sound is the ''reception'' of such waves and their ''perception'' by the ...
, visible signals enabled greater precision than audible ones, although audible signals could operate better under conditions of reduced visibility. The first
time ball
A time ball or timeball is a time-signalling device. It consists of a large, painted wooden or metal ball that is dropped at a predetermined time, principally to enable navigators aboard ships offshore to verify the setting of their marine chron ...
was erected at
Portsmouth
Portsmouth ( ) is a port and city in the ceremonial county of Hampshire in southern England. The city of Portsmouth has been a unitary authority since 1 April 1997 and is administered by Portsmouth City Council.
Portsmouth is the most dens ...
, England in 1829 by its inventor
Robert Wauchope.
[Aubin, Davi]
The Heavens on Earth: Observatories and Astronomy in Nineteenth-Century Science and Culture
p.164. Duke University Press, 2010 One was installed in 1833 on the roof of the
Royal Observatory in
Greenwich
Greenwich ( , ,) is a town in south-east London, England, within the ceremonial county of Greater London. It is situated east-southeast of Charing Cross.
Greenwich is notable for its maritime history and for giving its name to the Greenwich ...
, London, and the time ball has dropped at 1:00 pm every day since then. The first American time ball went into service in 1845.
[ In New York City, the ceremonial ]Times Square Ball
The Times Square Ball is a time ball located in New York City's Times Square. Located on the roof of One Times Square, the ball is a prominent part of a New Year's Eve celebration in Times Square commonly referred to as the ball drop, where the ...
drop on New Year's Eve in Times Square
Times Square is a major commercial intersection, tourist destination, entertainment hub, and neighborhood in Midtown Manhattan, New York City. It is formed by the junction of Broadway, Seventh Avenue, and 42nd Street. Together with adjacent ...
is a vestige of a visual time signal.
Electrical time signals
United Kingdom
The first telegraph distribution of time signal in the United Kingdom, indeed, in the world, was initiated in 1852 by the Electric Telegraph Company
The Electric Telegraph Company (ETC) was a British telegraph company founded in 1846 by William Fothergill Cooke and John Ricardo. It was the world's first public telegraph company. The equipment used was the Cooke and Wheatstone telegraph, ...
in collaboration with the Astronomer Royal
Astronomer Royal is a senior post in the Royal Households of the United Kingdom. There are two officers, the senior being the Astronomer Royal dating from 22 June 1675; the junior is the Astronomer Royal for Scotland dating from 1834.
The post ...
. Greenwich Mean Time
Greenwich Mean Time (GMT) is the Local mean time, mean solar 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, i ...
was distributed by telegraph from the Greenwich Observatory
The Royal Observatory, Greenwich (ROG; known as the Old Royal Observatory from 1957 to 1998, when the working Royal Greenwich Observatory, RGO, temporarily moved south from Greenwich to Herstmonceux) is an observatory situated on a hill in G ...
. This included a system for synchronising the drop of the time ball at Greenwich with other time balls around the country, one of which was atop the Electric's offices in the Strand
Strand may refer to:
Topography
*The flat area of land bordering a body of water, a:
** Beach
** Shoreline
* Strand swamp, a type of swamp habitat in Florida
Places Africa
* Strand, Western Cape, a seaside town in South Africa
* Strand Street ...
.[
Other synchronised time balls were atop the ]Nelson Monument, Edinburgh
The Nelson Monument is a commemorative tower in honour of Vice Admiral Horatio Nelson, located in Edinburgh, Scotland. It is situated on top of Calton Hill, and provides a dramatic termination to the vista along Princes Street from the we ...
; the sailors' home Broomielaw
Broomielaw is a major thoroughfare in the city of Glasgow, Scotland. It runs adjacent to the River Clyde, on its north bank and forms the southern, waterside boundary of the city's International Financial Services District.
History
Named after ...
, Glasgow; Liverpool
Liverpool is a city and metropolitan borough in Merseyside, England. With a population of in 2019, it is the 10th largest English district by population and its metropolitan area is the fifth largest in the United Kingdom, with a popul ...
and one at Deal, Kent
Deal is a coastal town in Kent, England, which lies where the North Sea and the English Channel meet, north-east of Dover and south of Ramsgate. It is a former fishing, mining and garrison town whose history is closely linked to the anchora ...
, installed by the Admiralty
Admiralty most often refers to:
*Admiralty, Hong Kong
*Admiralty (United Kingdom), military department in command of the Royal Navy from 1707 to 1964
*The rank of admiral
*Admiralty law
Admiralty can also refer to:
Buildings
* Admiralty, Traf ...
.[Kieve, Jeffrey L., ''The Electric Telegraph: A Social and Economic History'', pp. 52-53, David and Charles, 1973 .]
United States
Telegraph signals were used regularly for time coordination by the United States Naval Observatory
United States Naval Observatory (USNO) is a scientific and military facility that produces geopositioning, navigation and timekeeping data for the United States Navy and the United States Department of Defense. Established in 1830 as the Depo ...
starting in 1865. By the late 1800s, many U.S. observatories were selling accurate time by offering a regional time signal service.
Sandford Fleming
Sir Sandford Fleming (January 7, 1827 – July 22, 1915) was a Scottish Canadian engineer and inventor. Born and raised in Scotland, he emigrated to colonial Canada at the age of 18. He promoted worldwide standard time zones, a prime meridian, ...
proposed a single 24-hour clock for the entire world. At a meeting of the Royal Canadian Institute on 8 February 1879 he linked it to the anti-meridian of Greenwich (now 180°). He suggested that standard 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 could be used locally, but they were subordinate to his single world 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 r ...
came into existence in the United States on 18 November 1883. Earlier, on 11 October 1883, the General Time Convention, forerunner to the American Railway Association
The American Railway Association (ARA) was an industry trade group representing railroads in the United States. The organization had its inception in meetings of General Managers and ranking railroad operating officials known as Time Table Conventi ...
, approved a plan that divided the United States into several 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. On that November day, the US Naval Observatory telegraphed a signal that coordinated noon at Eastern standard time with 11 am Central, 10 am Mountain, and 9 am Pacific standard time.
A March 1905 issue of ''The Technical World'' describes the role of the United States Naval Observatory as a source of time signals:
:''One of the most important functions of the Naval Observatory is found in the daily distribution of the correct time to every portion of the United States. This is effected by means of telegraphic signals, which are sent out from Washington at noon daily, except Sundays. The original object of this time service was to furnish mariners in the seaboard cities with the means of regulating their chronometers; but, like many another governmental activity, its scope has gradually broadened until it has become of general usefulness. The electrical impulse which goes forth from the Observatory at noon each day, now sets or regulates automatically more than 70,000 clocks located in all parts of the United States, and also serves, in each of the larger cities of the country, to release a time-ball located on some lofty building of central location. The dropping of the time-ball – accompanied, at some points, with the simultaneous firing of a cannon – is the signal for the regulation by hand of hundreds of other clocks and watches in the vicinity.''
Radio time sources
Dedicated time signal broadcasts
The telegraphic distribution of time signals was made obsolete by the use of AM, FM, shortwave radio
Shortwave radio is radio transmission using shortwave (SW) radio frequencies. There is no official definition of the band, but the range always includes all of the high frequency band (HF), which extends from 3 to 30 MHz (100 to 10 me ...
, Internet Network Time Protocol servers as well as atomic clock
An atomic clock is a clock that measures time by monitoring the resonant frequency of atoms. It is based on atoms having different energy levels. Electron states in an atom are associated with different energy levels, and in transitions betwee ...
s in satellite navigation
A satellite navigation or satnav system is a system that uses satellites to provide autonomous geo-spatial positioning. It allows satellite navigation devices to determine their location (longitude, latitude, and altitude/elevation) to high pr ...
systems. Since 1905 time signals have been transmitted by radio. There are dedicated radio time signal stations around the world.
Time stations operating in the longwave
In radio, longwave, long wave or long-wave, and commonly abbreviated LW, refers to parts of the radio spectrum with wavelengths longer than what was originally called the medium-wave broadcasting band. The term is historic, dating from the e ...
radio band have highly predictable radio propagation
Radio propagation is the behavior of radio waves as they travel, or are propagated, from one point to another in vacuum, or into various parts of the atmosphere.
As a form of electromagnetic radiation, like light waves, radio waves are affect ...
characteristics, which gives low uncertainty in the received time signals. Stations operating in the shortwave
Shortwave radio is radio transmission using shortwave (SW) radio frequencies. There is no official definition of the band, but the range always includes all of the high frequency band (HF), which extends from 3 to 30 MHz (100 to 10 me ...
band can cover wider areas with relatively low-power transmitters, but the varying distance that the signal travels increases the uncertainty of the time signal on a scale of milliseconds.
Radio time signal stations broadcast the time in both audible and machine-readable time code
A timecode (alternatively, time code) is a sequence of numeric codes generated at regular intervals by a timing synchronization system. Timecode is used in video production, show control and other applications which require temporal coordinatio ...
form that can be used as references for radio clocks and radio-controlled watches.
The audio portions of the shortwave WWV and WWVH
WWVH is the callsign of the U.S. National Institute of Standards and Technology's shortwave radio time signal station located at the Barking Sands Missile Range, in Kekaha, on the island of Kauai in the state of Hawaii.
WWVH is the Pacific si ...
broadcasts can also be heard by telephone. The time announcements are normally delayed by less than 30 ms when using land lines from within the continental United States, and the stability (delay variation) is generally < 1 ms. When mobile phones are used, the delays are often more than 100 ms due to the multiple access methods used to share cell channels. In rare instances when the telephone connection is made by satellite, the time is delayed by 250 to 500 ms.
These broadcasts are available by telephone by dialling US numbers (303) 499-7111 for WWV (Colorado), and (808) 335-4363 for WWVH (Hawaii). Calls, which are not toll-free, are disconnected after 2 minutes.
Loran-C
Loran-C is a hyperbolic radio navigation system that allows a receiver to determine its position by listening to low frequency radio signals that are transmitted by fixed land-based radio beacons. Loran-C combined two different techniques to ...
time signals may also be used for radio clock synchronization, by augmenting their highly accurate frequency transmissions with external measurements of the offsets of LORAN navigation signals against time standards.
General broadcasters
As radio receivers became more widely available, broadcasters included time information in the form of voice announcements or automated tones to accurately indicate the hour. The BBC #REDIRECT BBC #REDIRECT BBC
Here i going to introduce about the best teacher of my life b BALAJI sir. He is the precious gift that I got befor 2yrs . How has helped and thought all the concept and made my success in the 10th board exam. ...
...
in its broadcasts from 1922.