Clocks; a watch-maker seated at his workbench
"Universal Clock" at the Clock Museum in Zacatlán, Puebla, Mexico

Study of the measurement of time.

- Horology

230 related topics



SSW facing, vertical declining sundial on the Moot Hall in Aldeburgh, Suffolk, England. The gnomon is a rod that is very narrow, so it functions as the style. The Latin motto loosely translates as "I only count the sunny hours."
A horizontal dial commissioned in 1862, the gnomon is the triangular blade. The style is its inclined edge.
A combined analemmatic-equatorial sundial in Ann Morrison Park in Boise, Idaho, 43°36'45.5"N 116°13'27.6"W
Wall sundial in Žiča Monastery, Serbia.
Sundial from the 18th century on the front wall of the former Evangelical school in Szprotawa, Poland.
Top view of an equatorial sundial. The hour lines are spaced equally about the circle, and the shadow of the gnomon (a thin cylindrical rod) moving from 3:00a.m. to 9:00p.m. on or around Solstice, when the Sun is at its highest declination.
Sundial in Singapore Botanic Gardens. The fact that Singapore is located almost at the equator is reflected in its design.
World's oldest sundial, from Egypt's Valley of the Kings (c. 1500 BC)
A London type horizontal dial. The western edge of the gnomon is used as the style before noon, the eastern edge after that time. The changeover causes a discontinuity, the noon gap, in the time scale.
Southern-hemisphere sundial in Perth, Australia. Magnify to see that the hour marks run anticlockwise. Note graph above the gnomon of the Equation of Time, needed to correct sundial readings.
The Equation of Time – above the axis the equation of time is positive, and a sundial will appear fast relative to a clock showing local mean time. The opposites are true below the axis.
The Whitehurst & Son sundial made in 1812, with a circular scale showing the equation of time correction. This is now on display in the Derby Museum.
Sunquest sundial, designed by Richard L. Schmoyer, at the Mount Cuba Observatory in Greenville, Delaware.
Sundial on the Orihuela Campus of Miguel Hernández University, Spain, which uses a projected graph of the equation of time within the shadow to indicate clock time.
The 1959 Carefree sundial in Carefree, Arizona has a 62 ft gnomon, possibly the largest sundial in the United States.
Timepiece, St Katharine Docks, London (1973) an equinoctial dial by Wendy Taylor
An equatorial sundial in the Forbidden City, Beijing. 39.9157°N, 116.3904°W The gnomon points true North and its angle with horizontal equals the local latitude. Closer inspection of the [[:File:beijing sundial.jpg|full-size image]] reveals the "spider-web" of date rings and hour-lines.
Horizontal sundial in Minnesota. June 17, 2007 at 12:21. 44°51′39.3″N, 93°36′58.4″W
Crude sundial near Johnson Space Center
Detail of horizontal sundial outside Kew Palace in London, United Kingdom
Two vertical dials at Houghton Hall Norfolk UK 52.82747°N, 0.65762°W. The left and right dials face South and East, respectively. Both styles are parallel, their angle to the horizontal equaling the latitude. The East-facing dial is a polar dial with parallel hour-lines, the dial-face being parallel to the style.
"Double" sundials in Nové Město nad Metují, Czech Republic; the observer is facing almost due north.
Polar sundial at Melbourne Planetarium
Effect of declining on a sundial's hour-lines. A vertical dial, at a latitude of 51° N, designed to face due South (far left) shows all the hours from 6am to 6pm, and has converging hour-lines symmetrical about the noon hour-line. By contrast, a West-facing dial (far right) is polar, with parallel hour lines, and shows only hours after noon.  At the intermediate orientations of South-Southwest, Southwest, and West-Southwest, the hour lines are asymmetrical about noon, with the morning hour-lines ever more widely spaced.
Two sundials, a large and a small one, at Fatih Mosque, Istanbul dating back to the late 16th century. It is on the southwest facade with an azimuth angle of 52° N.
Vertical reclining dial in the Southern Hemisphere, facing due north, with hyperbolic declination lines and hour lines. Ordinary vertical sundial at this latitude (between tropics) could not produce a declination line for the summer solstice. This particular sundial is located at the Valongo Observatory of the Federal University of Rio de Janeiro, Brazil.
Equatorial bow sundial in Hasselt, Flanders in Belgium 50.92972°N, 5.34194°W. The rays pass through the narrow slot, forming a uniformly rotating sheet of light that falls on the circular bow. The hour-lines are equally spaced; in this image, the local solar time is roughly 15:00 hours (3 p.m.). On September 10, a small ball, welded into the slot casts a shadow on centre of the hour band.
Precision sundial in Bütgenbach, Belgium.
50.4231°N, 6.2017°W (Google Earth)
Universal ring dial. The dial is suspended from the cord shown in the upper left; the suspension point on the vertical meridian ring can be changed to match the local latitude. The center bar is twisted until a sunray passes through the small hole and falls on the horizontal equatorial ring. See Commons annotations for labels.
Analemmatic sundial on a meridian line in the garden of the abbey of Herkenrode in Hasselt (Flanders in Belgium)
Ottoman-style sundial with folded gnomon and a compass. Debbane Palace museum, Lebanon.
19th-century Tibetan Shepherd's Timestick
Navicula de Venetiis on display at Musée d'histoire des sciences de la Ville de Genève.
Kraków. 50.0614°N, 19.94°W The shadow of the cross-shaped nodus moves along a hyperbola which shows the time of the year, indicated here by the zodiac figures. It is 1:50 p.m. on 16 July, 25 days after the summer solstice.
Declination lines at solstices and equinox for sundials, located at different latitudes
Diptych sundial in the form of a lute, c. 1612. The gnomons-style is a string stretched between a horizontal and vertical face. This sundial also has a small nodus (a bead on the string) that tells time on the hyperbolic pelikinon, just above the date on the vertical face.
Benoy Sun Clock showing 6:00 p.m.
Stainless steel bifilar sundial in Italy
Noon mark from the Greenwich Royal Observatory. The analemma is the narrow figure-8 shape, which plots the equation of time (in degrees, not time, 1°=4 minutes) versus the altitude of the Sun at noon at the sundial's location. The altitude is measured vertically, the equation of time horizontally.
Angbuilgu, a portable sundial used in Korea during the Joseon period. The integrated magnetic compass aligns the instrument toward north pole.(National Museum of Korea)

A sundial is a horological device that tells the time of day (referred to as civil time in modern usage) when direct sunlight shines by the apparent position of the Sun in the sky.


Continued sequence of existence and events that occurs in an apparently irreversible succession from the past, through the present, into the future.

The flow of sand in an hourglass can be used to measure the passage of time. It also concretely represents the present as being between the past and the future.
Horizontal sundial in Taganrog
An old kitchen clock
A contemporary quartz watch, 2007
Chip-scale atomic clocks, such as this one unveiled in 2004, are expected to greatly improve GPS location.
Scale of time in Jain texts shown logarithmically
Time's mortal aspect is personified in this bronze statue by Charles van der Stappen.
Two-dimensional space depicted in three-dimensional spacetime. The past and future light cones are absolute, the "present" is a relative concept different for observers in relative motion.
Relativity of simultaneity: Event B is simultaneous with A in the green reference frame, but it occurred before in the blue frame, and occurs later in the red frame.
Views of spacetime along the world line of a rapidly accelerating observer in a relativistic universe. The events ("dots") that pass the two diagonal lines in the bottom half of the image (the past light cone of the observer in the origin) are the events visible to the observer.
Philosopher and psychologist William James

The study of these devices is called horology.


Device used to measure and indicate time.

The Shepherd Gate Clock at the Royal Observatory, Greenwich
Clock face of the Elizabeth Tower in London, also known as Big Ben
Digital clock radio
Clock on the Beaux Arts façade of the Gare d'Orsay from Paris
24-hour clock face in Florence
Simple horizontal sundial
The flow of sand in an hourglass can be used to keep track of elapsed time
A water clock for goldbeating goldleaf in Mandalay (Myanmar)
A scale model of Su Song's Astronomical Clock Tower, built in 11th-century Kaifeng, China. It was driven by a large waterwheel, chain drive, and escapement mechanism
An elephant clock in a manuscript by Al-Jazari (1206 AD) from The Book of Knowledge of Ingenious Mechanical Devices
A 17th-century weight-driven clock
Richard of Wallingford pointing to a clock, his gift to St Albans Abbey
16th-century clock machine Convent of Christ, Tomar, Portugal
Lantern clock, German,
The Dutch polymath and horologist Christiaan Huygens, the inventor of first precision timekeeping devices (pendulum clock and spiral-hairspring watch)
Opened-up pocket watch
Early French electromagnetic clock
Picture of a quartz crystal resonator, used as the timekeeping component in quartz watches and clocks, with the case removed. It is formed in the shape of a tuning fork. Most such quartz clock crystals vibrate at a frequency of 32,768 Hz
Balance wheel, the oscillator in a mechanical mantel clock.
The Shepherd Gate Clock receives its timing signal from within the Royal Observatory, Greenwich.
Synchronous electric clock, around 1940. By 1940 the synchronous clock became the most common type of clock in the U.S.
A modern quartz clock with a 24-hour face
A linear clock at London's Piccadilly Circus tube station. The 24 hour band moves across the static map, keeping pace with the apparent movement of the sun above ground, and a pointer fixed on London points to the current time.
Software word clock
Many cities and towns traditionally have public clocks in a prominent location, such as a town square or city center. This one is on display at the center of the town of Robbins, North Carolina
A Napoleon III mantel clock, from the third quarter of the 19th century, in the Museu de Belles Arts de València from Spain
A monumental conical pendulum clock by Eugène Farcot, 1867. Drexel University, Philadelphia, USA
One mechanical clock (was useful for sailing purposes)
Mechanical digital clock (with rolling numbers)
Matthew Norman carriage clock with winding key
Decorated William Gilbert mantel clock
Digital clock displaying time by controlling valves on the fountain
Simplistic digital clock radio
Diagram of a mechanical digital display of a flip clock

Traditionally, in horology, the term clock was used for a striking clock, while a clock that did not strike the hours audibly was called a timepiece.

Columbia, Pennsylvania

Borough in Lancaster County, Pennsylvania, United States.

Downtown Columbia
Columbia Market House
Columbia, about 1905
Wright's Ferry Mansion

It is notable today as the site of one of the world's few museums devoted entirely to horology.

Water clock

Any timepiece by which time is measured by the regulated flow of liquid into (inflow type) or out from (outflow type) a vessel, and where the amount is then measured.

A display of two outflow water clocks from the Ancient Agora Museum in Athens. The top is an original from the late 5th century BC. The bottom is a reconstruction of a clay original.
Fragment of a basalt water-clock, with evaporation time markers on interior as dots on djed and was hieroglyphs. Late period, 30th Dynasty. From Egypt. The Petrie Museum of Egyptian Archaeology, London
The water-powered mechanism of Su Song's astronomical clock tower, featuring a clepsydra tank, waterwheel, escapement mechanism, and chain drive to power an armillary sphere and 113 striking clock jacks to sound the hours and to display informative plaques
Ancient Persian clock
An early 19th-century illustration of Ctesibius's (285–222 BC) clepsydra from the 3rd century BC. The hour indicator ascends as water flows in. Also, a series of gears rotate a cylinder to correspond to the temporal hours.
Al-Jazari's elephant water clock (1206).
Water-powered automatic castle clock of Al-Jazari, 12th century.
An incomplete scaled-down model of Jang Yeong-sil's self-striking water clock

Between 270 BC and AD 500, Hellenistic (Ctesibius, Hero of Alexandria, Archimedes) and Roman horologists and astronomers were developing more elaborate mechanized water clocks.

British Horological Institute

A turret clock in the museum display
Upton Hall
A Post Office speaking clock machine, on display at the museum

The British Horological Institute (BHI) is the representative body of the horological industry in the United Kingdom.


Science of the measurement of time, or timekeeping.

An hourglass, a universally known symbol of time, and earlier device for keeping track of time.
Chronos, the Greeks' personification of time.
A diagram depicting features of the human ciradian cycle (biological clock).
An artistic illustration of the tracking of the earth's history through geology.
Ancient Egyptian sundial, where daytime is split into 12 parts.

Also, of similarity to chronometry is horology, the study of time, however it is commonly used specifically with reference to the mechanical instruments created to keep time, with examples such as stopwatches, clocks, and hourglasses.

John Harrison

Self-educated English carpenter and clockmaker who invented the marine chronometer, a long-sought-after device for solving the problem of calculating longitude while at sea.

P. L. Tassaert's half-tone print of Thomas King's original 1767 portrait of John Harrison, located at the Science and Society Picture Library, London
Thomas King's 1767 portrait of John Harrison, located at the Science and Society Picture Library, London
Woodcut of cross section of English longcase (grandfather) clock movement from the mid-1800s
Longitude lines on the globe
Henry Sully's clock (Fig.1) with escapement (Fig.2) and shipboard gimbaled suspension mechanism (Fig.7).
Grasshopper escapement
Harrison's first sea clock (H1)
Harrison's second sea clock (H2)
Harrison's third sea clock (H3)
Drawings of Harrison's H4 chronometer of 1761, published in The principles of Mr Harrison's time-keeper, 1767.
Harrison's "sea watch" No.1 (H4), with winding crank
The clockwork in Harrison's H4 watch
Harrison's Chronometer H5, (Collection of the Worshipful Company of Clockmakers), in the Science Museum, London
A John Harrison ship chronometer
Captain James Cook, painted by Nathaniel Dance-Holland.
Harrison's tomb at St John-at-Hampstead.
Blue plaque in Red Lion Square in London
A modern memorial in Westminster Abbey
Bronze statue of John Harrison in Barrow upon Humber, Lincolnshire
Clock B at the Royal Observatory

Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time became the first popular bestseller on the subject of horology.

Edmund Beckett, 1st Baron Grimthorpe

"Bells" Baron Grimthorpe as caricatured by Spy (Leslie Ward) in Vanity Fair, February 1889
The Trinity College Clock mechanism was designed by Lord Grimthorpe
St Chad's Church, Far Headingley
The grave of Lord Grimthorpe outside St Albans Cathedral

Edmund Beckett, 1st Baron Grimthorpe, KC (12 May 1816 – 29 April 1905), known previously as Sir Edmund Beckett, 5th Baronet and Edmund Beckett Denison, was a "lawyer, mechanician and controversialist" as well as a noted horologist and architect.

International Museum of Horology

Tall case clock with multiple complications by Antide Janvier La Chaux-de-Fonds.
Marine Chronometer No. 3153 by Breguet & Fils, double barrels, La Chaux-de-Fonds.
Bracket clock with base by Pierre Jaquet Droz La Chaux-de-Fonds.
Minitayre marine chronometer by Ferdinand BerthoudLa Chaux-de-Fonds

The International Museum of Horology, Musée international d'horlogerie, is a horological museum in La Chaux-de-Fonds, Switzerland.