A time signal is a visible, audible, mechanical, or electronic signal used as a reference to determine the time of day.
Church bells or voices announcing hours of prayer gave way to automatically operated chimes on public clocks; however, audible signals (even signal guns) have limited range. Busy seaports used a visual signal, the dropping of a ball, to allow mariners to check the chronometers used for navigation. The advent of electrical telegraphs allowed widespread and precise distribution of time signals from central observatories. Railways 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) 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.
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 was the only time standard the general public needed.
Accurate knowledge of time of day is essential for navigation, and ships carried the most accurate marine chronometers available, although they did not keep perfect time. A number of accurate audible or visible time signals were established in many seaport cities to enable navigators to set their chronometers.
In Vancouver, British Columbia, a "9 O'Clock Gun" is still shot every night at 9 pm. (This gun was brought to Stanley Park in 1894 by the Department of Fisheries originally to warn fishermen 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 lighthouse keeper detonated a stick of dynamite. Elsewhere in Canada, a "Noon Gun" is fired daily from the citadels in Halifax and Quebec City and from Signal Hill in St. John's, Newfoundland and Labrador.
In the same manner, a Noon Gun has been fired in Cape Town, South Africa, since 1806.The gun is fired daily from the Lion Battery at Signal Hill.
The Noonday Gun serves a similar purpose in Hong Kong. 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, England, at the Castle in Edinburgh, Scotland, and also at Perth in Australia to establish the time. The Edinburgh "One O'Clock Gun" is still in operation. A cannon located at the top of Santa Lucia Hill, in Santiago, Chile, is shot every noon.
In Rome, on the Janiculum, a hill west of the Tiber 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 to synchronise all the church bells of Rome. It was situated in Castel Sant'Angelo until 1903 when it was moved to Monte Mario for a few months until it was placed in its current position. The cannon was silenced from the start of WWII 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, Afghanistan.
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 whistles 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's power plant whistle has been reinstated several times by popular demand after numerous attempts to silence it.
In 1861 and 1862, the Edinburgh Post Office Directory published time gun maps relating the number of seconds required for the report of the time gun to reach various locations in the city. Because light travels much faster than sound, visible signals enabled greater precision than audible ones, although audible signals could operate better under conditions of reduced visibility. The first time ball was erected at Portsmouth, England in 1829 by its inventor Robert Wauchope.One was installed in 1833 on the roof of the Royal Observatory in 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 drop on New Year's Eve in Times Square is a vestige of a visual time signal.
The first telegraph distribution of time signal in the United Kingdom, indeed, in the world, was initiated in 1852 by the Electric Telegraph Company in collaboration with the Astronomer Royal. Greenwich Mean Time was distributed by telegraph from the Greenwich Observatory. 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.
Other synchronised time balls were atop the Nelson Monument, Edinburgh; the sailors' home Broomielaw, Glasgow; Liverpool and one at Deal, Kent, installed by the Admiralty.
Telegraph signals were used regularly for time coordination by the United States Naval Observatory starting in 1865.By the late 1800s, many U.S. observatories were selling accurate time by offering a regional time signal service.
Sandford Fleming 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 zones could be used locally, but they were subordinate to his single world time.
Standard time 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, approved a plan that divided the United States into several time zones. 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:
The telegraphic distribution of time signals was made obsolete by the use of AM, FM, shortwave radio, Internet Network Time Protocol servers as well as atomic clocks in satellite navigation 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 radio band have highly predictable radio propagation characteristics, which gives low uncertainty in the received time signals. Stations operating in the shortwave 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 form that can be used as references for radio clocks and radio-controlled watches.The audio portions of the shortwave WWV and WWVH 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 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.
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 has included time "pips" in its broadcasts from 1922.
In the United States many information-based radio stations (full-service, all-news and news/talk) also broadcast time signals at the beginning of the hour. In New York, WCBS and WINS have distinctive beginning-of-the-hour tones, though the WINS signal is only approximate (several seconds error)[ citation needed ]. WINS also has a tone at 30 minutes past the hour for those setting their clocks. WTIC uses the Morse code V for victory to the tune of Beethoven's 5th Symphony at the beginning of the hour continuously since 1943.
Stations using iBiquity Digital Corporation's "HD Radio" system are contractually requiredto delay their analog broadcast by about eight seconds so it remains in sync with the digital stream. Thus, network-generated time signals and service cues will also be delayed by about eight seconds (for this reason, when WBEN-AM in Buffalo, New York was broadcasting time markers and was simulcast on an FM station that broadcast in HD, the FM signal did not carry the time signal; WBEN does not broadcast in HD). Local signals may also be delayed.
The all-news radio stations of the CBS Radio Network, of which WCBS is the flagship, air a "bong" (at a frequency of 440 Hz, the standard musical note A) that immediately precedes each top-of-the-hour network newscast. (The same bong could be heard on the CBS Television Network, at the top of the hour immediately before the beginning of any televised program, in the 1960s and 1970s.) An automated "chirp" at one second before the hour signals a switch to the radio network broadcast. As an example, KNX, the CBS Radio Network all-news station in Los Angeles, broadcasts this "bong" sound on the hour. However, due to buffering of the digital broadcast on some computers, this signal may be delayed as much as 20 seconds from the actual start of the hour (this is presumably the same situation for all CBS Radio stations, as each station's digital stream is produced and distributed in a similar manner), though unlike program content which is on a broadcast delay for content concerns, the time signal airs as-is over-the-air, meaning it can sometimes be talked over during a live news event or sports play-by-play. KYW-AM in Philadelphia broadcasts a time signal at the top of the hour along with its jingle.
Bonneville International-owned news/talk station KSL (AM-FM) in Salt Lake City uses a "clang" that originates from the Nauvoo Bell on Temple Square in Salt Lake City which has been a staple on the station since the early 1960s.
In Canada, the national English-language non-commercial CBC Radio One network has broadcast the daily National Research Council Time Signal since 5 November 1939;the simulcast occurs daily at 1pm Eastern Time. Its French-language counterpart, Radio-Canada, broadcasts a similar signal at noon. Vancouver radio station CKNW also broadcasts time signals, using a chime every half-hour. The CBC's predecessor, the Canadian National Railways Radio network, broadcast the time signal over its Ottawa station, CNRO (originally CKCH), at 9 pm daily and also on its Moncton station, CNRA, beginning in 1923. CNRA closed in 1931 but the broadcasts continued on CNRO when the station was acquired by the Canadian Radio Broadcasting Commission in 1933 and by the CBC in 1936 before going national in 1939.
In Australia, many information-based radio stations broadcast time signals at the beginning of the hour, and a speaking clock service was also available until October 2019. However, the VNG dedicated time signal service has been discontinued.
In Cuba, Radio Reloj is a radio station which has a time signal over news. Radio Reloj translates to Clock Radio.
Program material, including time signals, that is transmitted digitally (e.g. DAB, Internet radio) can be delayed by tens of seconds due to buffering and error correction, making time signals received on a digital radio unreliable when accuracy is needed.
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.
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 custom and practice. An example of a kind of time standard can be a time scale, specifying a method for measuring divisions of time. A standard for civil time can specify both time intervals and time-of-day.
Universal Time is a time standard based on Earth's rotation. While originally it was mean solar time at 0° longitude, precise measurements of the Sun are difficult. Therefore, UT1 is computed from a measure of the Earth's angle with respect to the International Celestial Reference Frame (ICRF), called the Earth Rotation Angle. UT1 is the same everywhere on Earth. UT1 is required to follow the relationship
The 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 Depot of Charts and Instruments, it is one of the oldest scientific agencies in the United States, and remains the country's leading authority for astronomical and timing data for all purposes.
The Royal Observatory, Greenwich is an observatory situated on a hill in Greenwich Park in south east London, overlooking the River Thames to the north. It played a major role in the history of astronomy and navigation, and because the Prime Meridian passes through it, it gave its name to Greenwich Mean Time, the precursor to today's Coordinated Universal Time (UTC). The ROG has the IAU observatory code of 000, the first in the list. ROG, the National Maritime Museum, the Queen's House and the clipper ship Cutty Sark are collectively designated Royal Museums Greenwich.
Celestial navigation, also known as astronavigation, is the practice of position fixing using stars and other celestial bodies that enables a navigator to accurately determine their actual current physical position in space without having to rely solely on estimated positional calculations, commonly known as "dead reckoning", made in the absence of satellite navigation or other similar modern electronic or digital positioning means.
A radio clock or radio-controlled clock (RCC), and often (incorrectly) referred to as an atomic clock is a type of quartz clock or watch that is automatically synchronized to a time code transmitted by a radio transmitter connected to a time standard such as an atomic clock. Such a clock may be synchronized to the time sent by a single transmitter, such as many national or regional time transmitters, or may use the multiple transmitters used by satellite navigation systems such as Global Positioning System. Such systems may be used to automatically set clocks or for any purpose where accurate time is needed. RC clocks may include any feature available for a clock, such as alarm function, display of ambient temperature and humidity, broadcast radio reception, etc.
The Greenwich Time Signal (GTS), popularly known as the pips, is a series of six short tones broadcast at one-second intervals by many BBC Radio stations. The pips were introduced in 1924 and have been generated by the BBC since 1990 to mark the precise start of each hour. Their utility in calibration is diminishing as digital broadcasting entails time lags.
CHU is the call sign of a shortwave time signal radio station operated by the Institute for National Measurement Standards of the National Research Council. CHU's signal is used for continuous dissemination of official Canadian government time signals, derived from atomic clocks.
The National Research Council Time Signal is Canada's longest running radio program. Heard every day since November 5, 1939, shortly before 13:00 Eastern Time across the CBC Radio One network, it lasts between 15 and 60 seconds, ending exactly at 13:00. During standard time, the signal is at 13:00 Eastern Standard Time and during Daylight Saving Time, the signal is at 13:00 Eastern Daylight Saving Time.
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 chronometers. Accurate timekeeping is essential to the determination of longitude at sea.
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 centre of the city.
Ladd Observatory is an astronomical observatory at Brown University in Providence, Rhode Island. Founded in 1891 it was primarily designed for student instruction and also research. The facility operated a regional timekeeping service. It was responsible for the care and calibration of clocks on campus including one at Carrie Tower and another that rang the class bell at University Hall. Meteorological observations were made there from the time the building opened using recording weather instruments.
A clock network or clock system is a set of synchronized clocks designed to always show exactly the same time by communicating with each other. Clock networks usually consist of a central master clock kept in sync with an official time source, and one or more slave clocks which receive and display the time from the master.
The 9 O'Clock Gun is a cannon located in Vancouver, British Columbia, Canada, that is ordinarily fired daily at 21:00 (9 p.m.) PT.
A master clock is a precision clock that provides timing signals to synchronise slave clocks as part of a clock network. Networks of electric clocks connected by wires to a precision master pendulum clock began to be used in institutions like factories, offices, and schools around 1900. Today, many radio clocks are synchronised by radio signals or Internet connections to a worldwide time system called Coordinated Universal Time (UTC), which is governed by primary reference clocks implemented as atomic clocks in many countries.
The Shepherd Gate Clock is mounted on the wall outside the gate of the Royal Observatory, Greenwich building in Greenwich, Greater London. The clock, an early example of an electric clock, was a slave mechanism controlled by electric pulses transmitted by a master clock inside the main building. The network of master and slave clocks was constructed and installed by Charles Shepherd in 1852. The clock by the gate was probably the first to display Greenwich Mean Time to the public, and is unusual in using the 24-hour analog dial. Also it originally showed astronomical time which started at 12 noon not midnight.
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 world its successor Coordinated Universal Time (UTC), 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.
The history of longitude is a record of the effort, by astronomers, cartographers and navigators over the centuries, to discover a means of determining longitude.
The Port Chalmers time ball is a Victorian maritime Greenwich Mean Time signal located on Aurora Terrace on top of Observation Point in the port of Port Chalmers, New Zealand. It was established in 1867 by the Otago Provincial Council. The time ball fell precisely at 1 p.m. daily. Originally triggered by a grandfather clock, from 1882 onwards a telegraph signal from Wellington took over this function. It was removed in 1970, but a replacement was restored to service in 2020.