Astronomical clock
Encyclopedia
Clock
A clock is an instrument used to indicate, keep, and co-ordinate time. The word clock is derived ultimately from the Celtic words clagan and clocca meaning "bell". A silent instrument missing such a mechanism has traditionally been known as a timepiece...
with special mechanisms and dials to display astronomical information, such as the relative positions of the sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
, moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
, zodiac
Zodiac
In astronomy, the zodiac is a circle of twelve 30° divisions of celestial longitude which are centred upon the ecliptic: the apparent path of the Sun across the celestial sphere over the course of the year...
al constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
s, and sometimes major planet
Planet
A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...
s.
Definition
The term is loosely used to refer to any clock that shows, in addition to the time of day, astronomical information. This could include the location of the sun and moon in the sky, the age and phase of the moon, the position of the sun on the ecliptic and the current zodiac sign, the sidereal timeSidereal time
Sidereal time is a time-keeping system astronomers use to keep track of the direction to point their telescopes to view a given star in the night sky...
, and other astronomical data such as the moon's nodes (for indicating eclipses) or a rotating star map. The term should not be confused with astronomical regulator, a high precision but otherwise ordinary pendulum clock
Pendulum clock
A pendulum clock is a clock that uses a pendulum, a swinging weight, as its timekeeping element. The advantage of a pendulum for timekeeping is that it is a resonant device; it swings back and forth in a precise time interval dependent on its length, and resists swinging at other rates...
used in observatories.
Astronomical clocks usually represent the solar system using the geocentric model. The center of the dial is often marked with a disc or sphere representing the earth, located at the center of the solar system. The sun is often represented by a golden sphere (as it initially appeared in the Antikythera Mechanism
Antikythera mechanism
The Antikythera mechanism is an ancient mechanical computer designed to calculate astronomical positions. It was recovered in 1900–1901 from the Antikythera wreck. Its significance and complexity were not understood until decades later. Its time of construction is now estimated between 150 and 100...
, back in the 2nd century BC), shown rotating around the earth once a day around a 24 hour analog dial
24 hour analog dial
Clocks and watches with a 24-hour analog dial have an hour hand that makes one complete revolution, 360°, in a day...
. This view accords both with daily experience and with the philosophical world view of pre-Copernican
Copernican Revolution
The Copernican Revolution refers to the paradigm shift away from the Ptolemaic model of the heavens, which postulated the Earth at the center of the galaxy, towards the heliocentric model with the Sun at the center of our Solar System...
Europe.
History
Antikythera mechanism
The Antikythera mechanism is an ancient mechanical computer designed to calculate astronomical positions. It was recovered in 1900–1901 from the Antikythera wreck. Its significance and complexity were not understood until decades later. Its time of construction is now estimated between 150 and 100...
of ancient Greece
Ancient Greece
Ancient Greece is a civilization belonging to a period of Greek history that lasted from the Archaic period of the 8th to 6th centuries BC to the end of antiquity. Immediately following this period was the beginning of the Early Middle Ages and the Byzantine era. Included in Ancient Greece is the...
was used to calculate the positions of the sun, moon, and stars at any given point by use of complex mechanical gears. As Cicero
Cicero
Marcus Tullius Cicero , was a Roman philosopher, statesman, lawyer, political theorist, and Roman constitutionalist. He came from a wealthy municipal family of the equestrian order, and is widely considered one of Rome's greatest orators and prose stylists.He introduced the Romans to the chief...
later wrote in the 1st century BC, Archimedes
Archimedes
Archimedes of Syracuse was a Greek mathematician, physicist, engineer, inventor, and astronomer. Although few details of his life are known, he is regarded as one of the leading scientists in classical antiquity. Among his advances in physics are the foundations of hydrostatics, statics and an...
and Posidonius
Posidonius
Posidonius "of Apameia" or "of Rhodes" , was a Greek Stoic philosopher, politician, astronomer, geographer, historian and teacher native to Apamea, Syria. He was acclaimed as the greatest polymath of his age...
's orrery
Orrery
An orrery is a mechanical device that illustrates the relative positions and motions of the planets and moons in the Solar System in a heliocentric model. Though the Greeks had working planetaria, the first orrery that was a planetarium of the modern era was produced in 1704, and one was presented...
achieved virtually the same thing.
In the 11th century, the Song Dynasty
Song Dynasty
The Song Dynasty was a ruling dynasty in China between 960 and 1279; it succeeded the Five Dynasties and Ten Kingdoms Period, and was followed by the Yuan Dynasty. It was the first government in world history to issue banknotes or paper money, and the first Chinese government to establish a...
Chinese horologist, mechanical engineer, and astronomer Su Song
Su Song
Su Song was a renowned Chinese polymath who specialized himself as a statesman, astronomer, cartographer, horologist, pharmacologist, mineralogist, zoologist, botanist, mechanical and architectural engineer, poet, antiquarian, and ambassador of the Song Dynasty .Su Song was the engineer of a...
created a water-driven astronomical clock for his clock-tower of Kaifeng
Kaifeng
Kaifeng , known previously by several names , is a prefecture-level city in east-central Henan province, Central China. Nearly 5 million people live in the metropolitan area...
City. Su Song is noted for having incorporated an escapement
Escapement
In mechanical watches and clocks, an escapement is a device that transfers energy to the timekeeping element and enables counting the number of oscillations of the timekeeping element...
mechanism and earliest known endless power-transmitting chain drive
Chain drive
Chain drive is a way of transmitting mechanical power from one place to another. It is often used to convey power to the wheels of a vehicle, particularly bicycles and motorcycles...
for his clock-tower and armillary sphere
Armillary sphere
An armillary sphere is a model of objects in the sky , consisting of a spherical framework of rings, centred on Earth, that represent lines of celestial longitude and latitude and other astronomically important features such as the ecliptic...
to function (for more info see water clock
Water clock
A water clock or clepsydra is any timepiece in which time is measured by the regulated flow of liquid into or out from a vessel where the amount is then measured.Water clocks, along with sundials, are likely to be the oldest time-measuring instruments, with the only exceptions...
). Contemporary Muslim astronomers
Islamic astronomy
Islamic astronomy or Arabic astronomy comprises the astronomical developments made in the Islamic world, particularly during the Islamic Golden Age , and mostly written in the Arabic language. These developments mostly took place in the Middle East, Central Asia, Al-Andalus, and North Africa, and...
and engineers also constructed a variety of highly accurate astronomical clocks for use in their observatories
Observatory
An observatory is a location used for observing terrestrial or celestial events. Astronomy, climatology/meteorology, geology, oceanography and volcanology are examples of disciplines for which observatories have been constructed...
, such as the castle clock
Castle clock
A castle clock is a clock whose face is mounted outside a castle or perhaps a church tower. They may be elaborate or simple.Al-Jazari constructed an elaborate clock and described it in his Book of Knowledge of Ingenious Mechanical Devices in 1206. It was about 3,3 metres high , and had multiple...
(a water-powered astronomical clock) by Al-Jazari
Al-Jazari
Abū al-'Iz Ibn Ismā'īl ibn al-Razāz al-Jazarī was a Muslim polymath: a scholar, inventor, mechanical engineer, craftsman, artist, mathematician and astronomer from Al-Jazira, Mesopotamia, who lived during the Islamic Golden Age...
in 1206, and the astrolabic
Astrolabe
An astrolabe is an elaborate inclinometer, historically used by astronomers, navigators, and astrologers. Its many uses include locating and predicting the positions of the Sun, Moon, planets, and stars, determining local time given local latitude and longitude, surveying, triangulation, and to...
clock by Ibn al-Shatir
Ibn al-Shatir
Ala Al-Din Abu'l-Hasan Ali Ibn Ibrahim Ibn al-Shatir was an Arab Muslim astronomer, mathematician, engineer and inventor who worked as muwaqqit at the Umayyad Mosque in Damascus, Syria.-Astronomy:...
in the early 14th century.
The early development of mechanical clocks in Europe is not fully understood, but there is general agreement that by 1300 - 1330 there existed mechanical clocks (powered by weights rather than by water and using an escapement
Escapement
In mechanical watches and clocks, an escapement is a device that transfers energy to the timekeeping element and enables counting the number of oscillations of the timekeeping element...
) which were intended for two main purposes: for signalling and notification (e.g. the timing of services and public events), and for modelling the solar system. The latter is an inevitable development, because the astrolabe
Astrolabe
An astrolabe is an elaborate inclinometer, historically used by astronomers, navigators, and astrologers. Its many uses include locating and predicting the positions of the Sun, Moon, planets, and stars, determining local time given local latitude and longitude, surveying, triangulation, and to...
was used both by astronomers and astrologers, and it was natural to apply a clockwork drive to the rotating plate to produce a working model of the solar system. Medieval researcher Lynn White Jr. wrote:
The astronomical clocks developed by Richard of Wallingford
Richard of Wallingford
Richard of Wallingford was an English mathematician who made major contributions to astronomy/astrology and horology while serving as abbot of St Albans Abbey in Hertfordshire.-Biography:...
in St Albans
St Albans
St Albans is a city in southern Hertfordshire, England, around north of central London, which forms the main urban area of the City and District of St Albans. It is a historic market town, and is now a sought-after dormitory town within the London commuter belt...
during the 1330s, and by Giovanni de Dondi in Padua
Padua
Padua is a city and comune in the Veneto, northern Italy. It is the capital of the province of Padua and the economic and communications hub of the area. Padua's population is 212,500 . The city is sometimes included, with Venice and Treviso, in the Padua-Treviso-Venice Metropolitan Area, having...
between 1348 and 1364 are masterpieces of their type. They no longer exist, but detailed descriptions of their design and construction survive, and modern reproductions have been made. Wallingford's clock may have shown the sun, moon (age, phase, and node), stars and planets, and had, in addition, a wheel of fortune and an indicator of the state of the tide at London
London
London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...
Bridge. De Dondi's clock was a seven-faced construction with 107 moving parts, showing the positions of the sun, moon, and five planets, as well as religious feast days.
Both these clocks, and others like them, were probably less accurate than their designers would have wished. The gear ratios may have been exquisitely calculated, but their manufacture was somewhat beyond the mechanical abilities of the time, and they never worked reliably. Furthermore, in contrast to the intricate advanced wheelwork, the timekeeping mechanism in nearly all these clocks until the 16th century was the simple verge and foliot escapement, which had errors of at least half an hour a day.
Astronomical clocks were built as demonstration or exhibition pieces, to impress as much as to educate or inform. The challenge of building these masterpieces meant that clockmakers would continue to produce them, to demonstrate their technical skill and their patrons' wealth. The philosophical message of an ordered, heavenly-ordained universe, which accorded with the Gothic era view of the world, helps explain their popularity.
The growing interest in astronomy during the 18th century revived interest in astronomical clocks, less for the philosophical message, more for the accurate astronomical information that pendulum
Pendulum
A pendulum is a weight suspended from a pivot so that it can swing freely. When a pendulum is displaced from its resting equilibrium position, it is subject to a restoring force due to gravity that will accelerate it back toward the equilibrium position...
-regulated clocks could display.
Su Sung's Cosmic Engine
The Science Museum (London)Science Museum (London)
The Science Museum is one of the three major museums on Exhibition Road, South Kensington, London in the Royal Borough of Kensington and Chelsea. It is part of the National Museum of Science and Industry. The museum is a major London tourist attraction....
has a scale model of the 'Cosmic Engine', which Su Sung, a Chinese
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
polymath
Polymath
A polymath is a person whose expertise spans a significant number of different subject areas. In less formal terms, a polymath may simply be someone who is very knowledgeable...
, designed and constructed in China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
in 1092. This great astronomical hydromechanical clock tower was about ten meters high (about 30 feet) and featured a clock escapement
Escapement
In mechanical watches and clocks, an escapement is a device that transfers energy to the timekeeping element and enables counting the number of oscillations of the timekeeping element...
and was indirectly powered by rotating wheel either with falling water and liquid mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
which does not freeze during sub-zero temperatures and flows freely allowing operation of the clock during winter. Also there is a full-sized working replica of Su Sung's clock in the Republic of China (Taiwan)'s
Republic of China
The Republic of China , commonly known as Taiwan , is a unitary sovereign state located in East Asia. Originally based in mainland China, the Republic of China currently governs the island of Taiwan , which forms over 99% of its current territory, as well as Penghu, Kinmen, Matsu and other minor...
National Museum of Natural Science
National Museum of Natural Science
The National Museum of Natural Science is a national museum in Taichung, Taiwan.-Overview:The museum covers and is a six-venue complex housing: the Space IMAX Theater, Science Center, Life Science Hall, Human Cultures Hall, Global Environment Hall, and Botanical Garden.The Research and Collection...
, Taichung city
Taichung
-Demographics:Taichung’s population was an estimated 1,040,725 in August 2006. There are slightly more females in the city than males.24.32% of residents are children, while 16.63% are young people, 52.68% are middle-age, and 6.73% are elderly....
. This exquisite full-scale, fully functional replica is reported to be 12 meters (40 feet) in height and was painstakingly constructed from Su Sung's original descriptions and mechanical drawings.
Al-Jazari's Castle Clock
The most sophisticated water-poweredWater clock
A water clock or clepsydra is any timepiece in which time is measured by the regulated flow of liquid into or out from a vessel where the amount is then measured.Water clocks, along with sundials, are likely to be the oldest time-measuring instruments, with the only exceptions...
astronomical clock was Al-Jazari
Al-Jazari
Abū al-'Iz Ibn Ismā'īl ibn al-Razāz al-Jazarī was a Muslim polymath: a scholar, inventor, mechanical engineer, craftsman, artist, mathematician and astronomer from Al-Jazira, Mesopotamia, who lived during the Islamic Golden Age...
's castle clock, considered to be an early example of a programmable
Computer programming
Computer programming is the process of designing, writing, testing, debugging, and maintaining the source code of computer programs. This source code is written in one or more programming languages. The purpose of programming is to create a program that performs specific operations or exhibits a...
analog computer
Analog computer
An analog computer is a form of computer that uses the continuously-changeable aspects of physical phenomena such as electrical, mechanical, or hydraulic quantities to model the problem being solved...
, in 1206. It was a complex device that was about 3,3 meters high (11 feet), and had multiple functions alongside timekeeping. It included a display of the zodiac
Zodiac
In astronomy, the zodiac is a circle of twelve 30° divisions of celestial longitude which are centred upon the ecliptic: the apparent path of the Sun across the celestial sphere over the course of the year...
and the solar
Heliocentric orbit
A heliocentric orbit is an orbit around the Sun. All planets, comets, and asteroids in our Solar System are in such orbits, as are many artificial probes and pieces of debris. The moons of planets in the Solar System, by contrast, are not in heliocentric orbits as they orbit their respective planet...
and lunar orbit
Lunar orbit
In astronomy, lunar orbit refers to the orbit of an object around the Moon.As used in the space program, this refers not to the orbit of the Moon about the Earth, but to orbits by various manned or unmanned spacecraft around the Moon...
s, and a pointer in the shape of the crescent moon
Lunar phase
A lunar phase or phase of the moon is the appearance of the illuminated portion of the Moon as seen by an observer, usually on Earth. The lunar phases change cyclically as the Moon orbits the Earth, according to the changing relative positions of the Earth, Moon, and Sun...
which travelled across the top of a gate
Gate
A gate is a point of entry to a space enclosed by walls, or a moderately sized opening in a fence. Gates may prevent or control entry or exit, or they may be merely decorative. Other terms for gate include yett and port...
way, moved by a hidden cart
Cart
A cart is a vehicle designed for transport, using two wheels and normally pulled by one or a pair of draught animals. A handcart is pulled or pushed by one or more people...
and causing automatic doors
Gate operator
A gate operator is a mechanical device used to open and close a gate, such as one at the end of a driveway. There are two main types of electric gate openers hydraulic or electromechanical; these can be further slit into the following categories, worm driven, arm openers and underground openers...
to open, each revealing a mannequin
Mannequin
A mannequin is an often articulated doll used by artists, tailors, dressmakers, and others especially to display or fit clothing...
, every hour
Hour
The hour is a unit of measurement of time. In modern usage, an hour comprises 60 minutes, or 3,600 seconds...
.
It was possible to re-program the length of day
Daytime (astronomy)
On Earth, daytime is roughly the period on any given point of the planet's surface during which it experiences natural illumination from indirect or direct sunlight....
and night every day in order to account for the changing lengths of day and night throughout the year, and it also featured five musician automata
Automaton
An automaton is a self-operating machine. The word is sometimes used to describe a robot, more specifically an autonomous robot. An alternative spelling, now obsolete, is automation.-Etymology:...
who automatically played music when moved by lever
Lever
In physics, a lever is a rigid object that is used with an appropriate fulcrum or pivot point to either multiply the mechanical force that can be applied to another object or resistance force , or multiply the distance and speed at which the opposite end of the rigid object travels.This leverage...
s operated by a hidden camshaft
Camshaft
A camshaft is a shaft to which a cam is fastened or of which a cam forms an integral part.-History:An early cam was built into Hellenistic water-driven automata from the 3rd century BC. The camshaft was later described in Iraq by Al-Jazari in 1206. He employed it as part of his automata,...
attached to a water wheel
Water wheel
A water wheel is a machine for converting the energy of free-flowing or falling water into useful forms of power. A water wheel consists of a large wooden or metal wheel, with a number of blades or buckets arranged on the outside rim forming the driving surface...
. Other components of the castle clock included a main reservoir
Reservoir
A reservoir , artificial lake or dam is used to store water.Reservoirs may be created in river valleys by the construction of a dam or may be built by excavation in the ground or by conventional construction techniques such as brickwork or cast concrete.The term reservoir may also be used to...
with a float, a float chamber
Float chamber
A float chamber is a device for automatically regulating the supply of a liquid to a system. It is most typically found in the carburettor of a normally aspirated internal combustion engine, where it automatically meters the fuel supply to the engine...
and flow regulator
Regulator (automatic control)
In automatic control, a regulator is a device which has the function of maintaining a designated characteristic. It performs the activity of managing or maintaining a range of values in a machine. The measurable property of a device is managed closely by specified conditions or an advance set...
, plate and valve
Valve
A valve is a device that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but are usually discussed as a separate category...
trough, two pulley
Pulley
A pulley, also called a sheave or a drum, is a mechanism composed of a wheel on an axle or shaft that may have a groove between two flanges around its circumference. A rope, cable, belt, or chain usually runs over the wheel and inside the groove, if present...
s, crescent disc displaying the zodiac, and two falcon automata dropping balls into vases.
Strasbourg
Strasbourg Cathedral
Strasbourg Cathedral or the Cathedral of Our Lady of Strasbourg is a Roman Catholic cathedral in Strasbourg, France. Although considerable parts of it are still in Romanesque architecture, it is widely consideredSusan Bernstein: , The Johns Hopkins University Press to be among the finest...
has housed three different astronomical clocks since the 14th century.
The first clock was built between 1352 and 1354 and stopped working sometime at
the beginning of the 16th century. A second clock was then built by Herlin, Conrad Dasypodius
Conrad Dasypodius
Conrad Dasypodius was a professor of mathematics in Strasbourg, Alsace. He was born in Frauenfeld, Thurgau, Switzerland. His first name was also rendered as Konrad or Conradus or Cunradus, and his last name has been alternatively stated as Rauchfuss, Rauchfuß, and Hasenfratz...
, the Habrecht brothers, and others, between 1547 and 1574. This clock stopped working
in 1788 or 1789 (as it apparently stopped working gradually, each component being disconnected
one after the other). After a lapse of 50 years, a new clock was built
by Jean-Baptiste Schwilgué
Jean-Baptiste Schwilgué
Jean-Baptiste Schwilgué was the author of the third astronomical clock of Strasbourg Cathedral, built between 1838 and 1843 ....
(1776–1856) and about 30 workers. This clock is housed
in the case of the 2nd clock. It shows many astronomical and calendrical functions
(including what is thought to be the first complete mechanization of
the part of the computus
Computus
Computus is the calculation of the date of Easter in the Christian calendar. The name has been used for this procedure since the early Middle Ages, as it was one of the most important computations of the age....
needed to compute Easter) as well as several automata.
Prague
- See that article for an annotated diagram of its functions.
One of the most famous of this type of clock is the Old-Town Hall clock in Prague, Czech Republic. It is also known as the Prague Orloj. The central portion was completed in 1410. The four figures are set in motion at the hour, with Death (represented by a skeleton) striking the time. On the hour there is a presentation of statues of the Apostles at the doorways above the clock, with all twelve presented at noon. In 1870 a calendar display was added below the clock.
During World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
the clock was nearly destroyed by Nazi
Nazism
Nazism, the common short form name of National Socialism was the ideology and practice of the Nazi Party and of Nazi Germany...
fire. The townspeople are credited with heroic efforts in saving most of the parts. It was gradually renovated till 1948. In 1979 the clock was once more cleaned and renovated. According to local legend the city will suffer if the clock is neglected and its good operation is placed in jeopardy.
Olomouc
Olomouc
Olomouc is a city in Moravia, in the east of the Czech Republic. The city is located on the Morava river and is the ecclesiastical metropolis and historical capital city of Moravia. Nowadays, it is an administrative centre of the Olomouc Region and sixth largest city in the Czech Republic...
, the former capital of Moravia
Moravia
Moravia is a historical region in Central Europe in the east of the Czech Republic, and one of the former Czech lands, together with Bohemia and Silesia. It takes its name from the Morava River which rises in the northwest of the region...
in the eastern part of the Czech Republic, also has an impressive exterior astronomical clock on the main town square. It is a rare example of a heliocentric astronomical clock.
Dating originally from 1420, the clock was remodelled approximately once every century. When the retreating Nazi German army passed through Olomouc in the final days of the war in May 1945 they opened fire on the old astronomical clock, leaving only a few pieces (that can now be seen in the local museum). As a result of the serious damage the clock was reconstructed in the style of socialist-realism in the first years of communist rule in Czechoslovakia (late 1940s-early 1950s). The religious and royal figures were replaced with athletes, workers, farmers, scientists and other members of the proletariat, while the glockenspiel
Glockenspiel
A glockenspiel is a percussion instrument composed of a set of tuned keys arranged in the fashion of the keyboard of a piano. In this way, it is similar to the xylophone; however, the xylophone's bars are made of wood, while the glockenspiel's are metal plates or tubes, and making it a metallophone...
was altered to play three pieces of traditional local music.
The lower dial represents the earthly sphere and indicates minute, hour, day, month, year and phase of the moon. The upper dial represents the heavenly sphere and shows a star map, the sun, earth and planets against a background of the twelve houses of the zodiac. The third and highest level is where the saints and apostles once paraded during the daily musical display (at noon). Their role is now performed by faded-looking volleyball players, auto mechanics and factory workers.
The intricate background mosaic covers the clock's entire height of 14 metres and has representations of the twelve seasons and two traditional festivals; the ride of the kings and the procession of maidens.
The Olomouc astronomical clock was featured in the opening scenes of the film "The Joke" based on the book by Milan Kundera.
Astronomical clock of Taqi al-Din
The OttomanOttoman Empire
The Ottoman EmpireIt was usually referred to as the "Ottoman Empire", the "Turkish Empire", the "Ottoman Caliphate" or more commonly "Turkey" by its contemporaries...
engineer Taqi al-Din described a weight-driven clock with a verge-and-foliot escapement
Verge escapement
The verge escapement is the earliest known type of mechanical escapement, the mechanism in a mechanical clock that controls its rate by advancing the gear train at regular intervals or 'ticks'. Its origin is unknown. Verge escapements were used from the 14th century until about 1800 in clocks...
, a striking train of gears, an alarm
Alarm clock
An alarm clock is a clock that is designed to make a loud sound at a specific time. The primary use of these clocks is to awaken people from their night's sleep or short naps; they are sometimes used for other reminders as well. To stop the sound, a button or handle on the clock is pressed; but...
, and a representation of the moon's phases in his book The Brightest Stars for the Construction of Mechanical Clocks (Al-Kawākib al-durriyya fī wadh' al-bankāmat al-dawriyya), written around 1565. The clock also displayed the zodiac.
Lund
Lund Cathedral
The Lund Cathedral is the Lutheran cathedral in Lund, Scania, Sweden. It is the seat of the bishop of Lund of the Church of Sweden.- History :...
in Sweden
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
, Horologium mirabile Lundense was made at the end of the 14th century. After it had been in storage since 1837, it was restored and put back in place in 1923. When it plays, one can hear In Dulci Jubilo
In Dulci Jubilo
In dulci jubilo is a traditional Christmas carol. In its original setting, the carol is a macaronic text of German and Latin dating from the Middle Ages. Subsequent translations into English, such as J.M...
from the smallest organ in the church, while six wooden figures, representing the three magi
Magi
Magi is a term, used since at least the 4th century BC, to denote a follower of Zoroaster, or rather, a follower of what the Hellenistic world associated Zoroaster with, which...
and their servants, pass by Mary and Jesus.
Copenhagen
The city hallCopenhagen City Hall
Copenhagen City Hall is the headquarters of the Municipal Council as well as the Lord mayor of the City of Copenhagen, Denmark. The building is situated on The City Hall Square in central Copenhagen....
in Copenhagen
Copenhagen
Copenhagen is the capital and largest city of Denmark, with an urban population of 1,199,224 and a metropolitan population of 1,930,260 . With the completion of the transnational Øresund Bridge in 2000, Copenhagen has become the centre of the increasingly integrating Øresund Region...
has a complete astronomical clock
Jens Olsen's World Clock
Jens Olsen's World Clock or Verdensur is an advanced astronomical clock which is displayed in Copenhagen City Hall.The clock was designed and calculated by Jens Olsen who was a skilled locksmith, but later learned the trade of clockmaking...
, set in an interior glass cabinet.
The clock was designed over a period of 50 years by amateur astronomer and professional clockmaker Jens Olsen
Jens Olsen
Jens Olsen was a clockmaker, locksmith and astromechanic who built the famous world clock located in the city hall of Copenhagen, the Rådhus. He was born in Ribe, Denmark. Ever since he was a small child, Olsen was interested in clocks and other mechanical devices...
.
Some of the components (such as the computus) were inspired by the Strasbourg clock, which was studied
by Olsen. It was assembled from 1948 to 1955. Between 1995 and 1997 the clock underwent a complete restoration by the Danish watchmaker and conservator Søren Andersen.
The Rasmus Sørnes Clock
Rasmus Sørnes
Rasmus Jonassen Sørnes , inventor, clockmaker and radio technician, is most famous for his astronomical clocks, but also designed in his lifetime a large variety of agricultural, radio-technical and mechanical devices, only a few of them patented.Rasmus Sørnes was born in Sola in Norway in 1893...
(1893–1967), is characterized by its superior complexity compactly housed in a casing with the modest measurements of 0.70 x 0.60 x 2.10 m. Features include locations of the sun and moon in the zodiac, Julian calendar
Julian calendar
The Julian calendar began in 45 BC as a reform of the Roman calendar by Julius Caesar. It was chosen after consultation with the astronomer Sosigenes of Alexandria and was probably designed to approximate the tropical year .The Julian calendar has a regular year of 365 days divided into 12 months...
, Gregorian calendar
Gregorian calendar
The Gregorian calendar, also known as the Western calendar, or Christian calendar, is the internationally accepted civil calendar. It was introduced by Pope Gregory XIII, after whom the calendar was named, by a decree signed on 24 February 1582, a papal bull known by its opening words Inter...
, sidereal time
Sidereal time
Sidereal time is a time-keeping system astronomers use to keep track of the direction to point their telescopes to view a given star in the night sky...
, GMT, local time with daylight saving time and leap year, solar and lunar cycle corrections, eclipses, local sunset and sunrise, moonphase, tides, sunspot
Sunspot
Sunspots are temporary phenomena on the photosphere of the Sun that appear visibly as dark spots compared to surrounding regions. They are caused by intense magnetic activity, which inhibits convection by an effect comparable to the eddy current brake, forming areas of reduced surface temperature....
cycles and a planetarium
Planetarium
A planetarium is a theatre built primarily for presenting educational and entertaining shows about astronomy and the night sky, or for training in celestial navigation...
including Pluto
Pluto
Pluto, formal designation 134340 Pluto, is the second-most-massive known dwarf planet in the Solar System and the tenth-most-massive body observed directly orbiting the Sun...
's 248 year orbit and the 25 800 year period of the polar ecliptics (precession
Precession
Precession is a change in the orientation of the rotation axis of a rotating body. It can be defined as a change in direction of the rotation axis in which the second Euler angle is constant...
of the Earth's axis). All wheels are in brass and gold plated. Dials are silver plated.
Sørnes also made the necessary tools and based his work on his own observations of the firmament. This remarkable timepiece will probably be the last one ever to be designed and made by hand by one single person as true craftsmanship and a work of art. The result, outstanding for its performance and accuracy, remains a symbol of the transition from the mechanical age, Sørnes' electromechanical pendulum system pointing forward into the age of digital clocks. Having been exhibited at the Time Museum in Rockford, Illinois, and at The Chicago Museum of Science and Industry, the clock was sold in 2002 and its current location is not known. The Rasmus Sørnes Astronomical Clock no.3, the precursor to the Chicago Clock, his tools, patents, drawings, telescope and other items, are exhibited at the Borgarsyssel Museum
Borgarsyssel Museum
Borgarsyssel Museum is a museum in Sarpsborg, Norway.It was founded in 1921, and named after Borgarsysla, the Norse name of Østfold county. Since 1947 it is the main county museum of Østfold. Since 1 January 2006 it is a part of the foundation Østfoldmuseet, which organizes all museums in the...
in Sarpsborg
Sarpsborg
is a city and municipality in Østfold county, Norway. The administrative centre of the municipality is the city of Sarpsborg.Sarpsborg is part of the fifth largest urban area in Norway when paired with neighbouring Fredrikstad...
, Norway
Norway
Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...
.
Table clocks
There are many examples of astronomical table clocks, due to their popularity as showpieces. To become a master clockmaker in 17th century Augsburg candidates had to design and build a 'masterpiece' clock, an astronomical table top clock of formidable complexity. Examples can be found in museums, such as London's British MuseumBritish Museum
The British Museum is a museum of human history and culture in London. Its collections, which number more than seven million objects, are amongst the largest and most comprehensive in the world and originate from all continents, illustrating and documenting the story of human culture from its...
.
Currently Edmund Scientific among other retailers offer a mechanical Tellurium clock, perhaps the first mechanical astronomical clock to be mass marketed.
Watches
More recently, independent clockmaker Christiaan van der Klaauw created a wristwatch astrolabe, the "Astrolabium" in addition to the "Planetarium 2000", the "Eclipse 2001" and the "Real Moon." Ulysse NardinUlysse Nardin
Ulysse Nardin is a watch manufacturer founded in 1846 in Le Locle, Switzerland. Historically Ulysse Nardin was best known for being a manufacturer of marine chronometers, but today Ulysse Nardin produces complicated mechanical watches.-History:...
also sells several astronomical wristwatches, the "Astrolabium," "Planetarium", and the "Tellurium J. Kepler."
Others
Many European countries have examples of astronomical clocks, including:
Italy
- Messina. The Orologio astronomico di Messina. Multi-dial clock equipped with some of the most complex automata. Reconstructed between 1930 and 1933 on the base of the original dating from 1574.
- CremonaCremonaCremona is a city and comune in northern Italy, situated in Lombardy, on the left bank of the Po River in the middle of the Pianura Padana . It is the capital of the province of Cremona and the seat of the local City and Province governments...
. The Torrazzo, the bell tower of the Cremona CathedralCremona CathedralThe Duomo di Cremona , dedicated to Santa Maria Assunta , is a church in Cremona, Lombardy, northern Italy and the episcopal see of the Roman Catholic Diocese of Cremona...
, contains the largest medieval clock in Europe. - MantuaMantuaMantua is a city and comune in Lombardy, Italy and capital of the province of the same name. Mantua's historic power and influence under the Gonzaga family, made it one of the main artistic, cultural and notably musical hubs of Northern Italy and the country as a whole...
. The Palazzo della Ragione with the "Tower of the Clock" - VeniceVeniceVenice is a city in northern Italy which is renowned for the beauty of its setting, its architecture and its artworks. It is the capital of the Veneto region...
. St Mark's ClockSt Mark's ClockFor the building containing the clock see the article on the ClocktowerSt Mark's Clock is the clock housed in the Clocktower on the Piazza San Marco in Venice adjoining the Procuratie Vecchie...
, in the clocktowerSt Mark's ClocktowerThe Clock Tower in Venice is an early renaissance building on the north side of the Piazza San Marco at the entrance to the Merceria. It comprises a tower, which contains the clock, and lower buildings on each side. It adjoins the eastern end of the Procuratie Vecchie...
on St Mark's Square, was built and installed by Gian Paulo and Gian Carlo Rainieri, father and son, between 1496 and 1499. - BresciaBresciaBrescia is a city and comune in the region of Lombardy in northern Italy. It is situated at the foot of the Alps, between the Mella and the Naviglio, with a population of around 197,000. It is the second largest city in Lombardy, after the capital, Milan...
.
United Kingdom
- ExeterExeterExeter is a historic city in Devon, England. It lies within the ceremonial county of Devon, of which it is the county town as well as the home of Devon County Council. Currently the administrative area has the status of a non-metropolitan district, and is therefore under the administration of the...
. The clock in Exeter CathedralExeter CathedralExeter Cathedral, the Cathedral Church of Saint Peter at Exeter, is an Anglican cathedral, and the seat of the Bishop of Exeter, in the city of Exeter, Devon in South West England....
is one of the group of famous 14th to 16th century astronomical clocks to be found in the West of England. The main, lower, dial is the oldest part of the clock, probably dating from the 1480s. - WellsWellsWells is a cathedral city and civil parish in the Mendip district of Somerset, England, on the southern edge of the Mendip Hills. Although the population recorded in the 2001 census is 10,406, it has had city status since 1205...
. The Wells Cathedral clockWells Cathedral clockThe Wells Cathedral clock is an astronomical clock in the north transept of Wells Cathedral, England.The clock is one of the group of famous 14th to 16th century astronomical clocks to be found in the West of England....
is an astronomical clock in the north transeptTranseptFor the periodical go to The Transept.A transept is a transverse section, of any building, which lies across the main body of the building. In Christian churches, a transept is an area set crosswise to the nave in a cruciform building in Romanesque and Gothic Christian church architecture...
of Wells CathedralWells CathedralWells Cathedral is a Church of England cathedral in Wells, Somerset, England. It is the seat of the Bishop of Bath and Wells, who lives at the adjacent Bishop's Palace....
, England. It can be dated to between 1386 and 1392. - Ottery St MaryOttery St MaryOttery St Mary, known as "Ottery" , is a town in the East Devon district of Devon, England, on the River Otter, about ten miles east of Exeter on the B3174. It is part of a large civil parish of the same name, which also covers the villages of West Hill, Metcombe, Fairmile, Alfington, Tipton St...
. - Wimborne.
- LeicesterLeicesterLeicester is a city and unitary authority in the East Midlands of England, and the county town of Leicestershire. The city lies on the River Soar and at the edge of the National Forest...
. An astronomical clock can be found at the University of Leicester opposite the Physic department. - Hampton Court PalaceHampton Court PalaceHampton Court Palace is a royal palace in the London Borough of Richmond upon Thames, Greater London; it has not been inhabited by the British royal family since the 18th century. The palace is located south west of Charing Cross and upstream of Central London on the River Thames...
. The interior facade of the Main Gatehouse contains a fine early example of a post-Copernican astronomical clock. - YorkYorkYork is a walled city, situated at the confluence of the Rivers Ouse and Foss in North Yorkshire, England. The city has a rich heritage and has provided the backdrop to major political events throughout much of its two millennia of existence...
. The astronomical clock that resides in York MinsterYork MinsterYork Minster is a Gothic cathedral in York, England and is one of the largest of its kind in Northern Europe alongside Cologne Cathedral. The minster is the seat of the Archbishop of York, the second-highest office of the Church of England, and is the cathedral for the Diocese of York; it is run by...
, although modern, is a prime example of an astronomical clock, and was built to commemorate the RAF and Commonwealth nations' efforts in World War IIWorld War IIWorld War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
.
France
- VersaillesVersaillesVersailles , a city renowned for its château, the Palace of Versailles, was the de facto capital of the kingdom of France for over a century, from 1682 to 1789. It is now a wealthy suburb of Paris and remains an important administrative and judicial centre...
. The Palace of VersaillesPalace of VersaillesThe Palace of Versailles , or simply Versailles, is a royal château in Versailles in the Île-de-France region of France. In French it is the Château de Versailles....
near ParisParisParis is the capital and largest city in France, situated on the river Seine, in northern France, at the heart of the Île-de-France region...
has a rococoRococoRococo , also referred to as "Late Baroque", is an 18th-century style which developed as Baroque artists gave up their symmetry and became increasingly ornate, florid, and playful...
astronomical clock sitting on a formal low marble base. It took 12 years for a clockmaker and an engineer to build and was presented to Louis XVLouis XV of FranceLouis XV was a Bourbon monarch who ruled as King of France and of Navarre from 1 September 1715 until his death. He succeeded his great-grandfather at the age of five, his first cousin Philippe II, Duke of Orléans, served as Regent of the kingdom until Louis's majority in 1723...
in 1754. - RouenRouenRouen , in northern France on the River Seine, is the capital of the Haute-Normandie region and the historic capital city of Normandy. Once one of the largest and most prosperous cities of medieval Europe , it was the seat of the Exchequer of Normandy in the Middle Ages...
. The Gros Horloge is a famous astronomical clock with a movement dating back to the 14th century, though the facade is more recent. It is located in the Gros Horloge street. - LyonLyonLyon , is a city in east-central France in the Rhône-Alpes region, situated between Paris and Marseille. Lyon is located at from Paris, from Marseille, from Geneva, from Turin, and from Barcelona. The residents of the city are called Lyonnais....
. The cathedral also has an astronomical clock from the 14th century. - HaguenauHaguenau-Economy:The town has a well balanced economy. Centuries of troubled history in the buffer lands between France and Germany have bequeathed to Haguenau a rich historical and cultural heritage which supports a lively tourist trade. There is also a thriving light manufacturing sector centred on the...
. The Renaissance building of the former chancellery (now housing the Musée alsacien) displays an astronomical clock on its facade.
Denmark
- RoskildeRoskildeRoskilde is the main city in Roskilde Municipality, Denmark on the island of Zealand. It is an ancient city, dating from the Viking Age and is a member of the Most Ancient European Towns Network....
Norway
- OsloOsloOslo is a municipality, as well as the capital and most populous city in Norway. As a municipality , it was established on 1 January 1838. Founded around 1048 by King Harald III of Norway, the city was largely destroyed by fire in 1624. The city was moved under the reign of Denmark–Norway's King...
Germany
- StendalStendalStendal is a town in Saxony-Anhalt, Germany. It is the capital of Stendal District and unofficial capital of the Altmark. Its population in 2001 was 38,900. It is located some west of Berlin and around east of Hanover...
- MünsterMünsterMünster is an independent city in North Rhine-Westphalia, Germany. It is located in the northern part of the state and is considered to be the cultural centre of the Westphalia region. It is also capital of the local government region Münsterland...
.St. Paul's Cathedral, includes an astronomical clock of 1540, adorned with hand-painted zodiac symbols, which traces the movement of the planets, and plays a GlockenspielGlockenspielA glockenspiel is a percussion instrument composed of a set of tuned keys arranged in the fashion of the keyboard of a piano. In this way, it is similar to the xylophone; however, the xylophone's bars are made of wood, while the glockenspiel's are metal plates or tubes, and making it a metallophone...
tune every noon. - RostockRostockRostock -Early history:In the 11th century Polabian Slavs founded a settlement at the Warnow river called Roztoc ; the name Rostock is derived from that designation. The Danish king Valdemar I set the town aflame in 1161.Afterwards the place was settled by German traders...
. St. Mary's ChurchSt. Mary's Church, RostockSt. Mary's Church, Rostock, in German Marienkirche, is the biggest of three town churches found in the Hanseatic city of Rostock, in northern Germany. The other two are St. Petri and St. Nicholas . A fourth, St. James , was heavily damaged during the Second World War and subsequently demolished. St...
with astronomical clock, dating from 1472, built by Hans DüringerHans DüringerHans Düringer was a clockmaker from Nuremberg in Germany who died 1477 in Rostock. His most famous works are the astronomical clocks in St.Mary's Church, Danzig 1470 and St...
. Clock with daily time, zodiac, moon phases, and month. Calendar, which is valid until 2017. - Esslingen. At the headquarters of Festo, Professor Hans Scheurenbrand has constructed the Harmonices Mundi (named after Kepler's book of the same name), which consists of a technologically sophisticated astronomical clock, a world time clock, and a 74 bell glockenspielGlockenspielA glockenspiel is a percussion instrument composed of a set of tuned keys arranged in the fashion of the keyboard of a piano. In this way, it is similar to the xylophone; however, the xylophone's bars are made of wood, while the glockenspiel's are metal plates or tubes, and making it a metallophone...
.
Switzerland
- Bern. The ZytgloggeZytgloggeThe Zytglogge tower is a landmark medieval tower in Bern, Switzerland. Built in the early 13th century, it has served the city as guard tower, prison, clock tower, centre of urban life and civic memorial....
is a famous astronomical clock from the 15th century situated in the landmark medieval tower of the same name. - SionSion, SwitzerlandSion is the capital of the Swiss canton of Valais. it had a population of .Landmarks include the Basilique de Valère and Château de Tourbillon. Sion has an airfield for civilian and military use, which, because of its location in a valley, causes a reasonable amount of noise pollution. FC Sion...
- WinterthurWinterthurWinterthur is a city in the canton of Zurich in northern Switzerland. It has the country's sixth largest population with an estimate of more than 100,000 people. In the local dialect and by its inhabitants, it is usually abbreviated to Winti...
Croatia
- SplitSplit (city)Split is a Mediterranean city on the eastern shores of the Adriatic Sea, centered around the ancient Roman Palace of the Emperor Diocletian and its wide port bay. With a population of 178,192 citizens, and a metropolitan area numbering up to 467,899, Split is by far the largest Dalmatian city and...
Poland
- GdanskGdanskGdańsk is a Polish city on the Baltic coast, at the centre of the country's fourth-largest metropolitan area.The city lies on the southern edge of Gdańsk Bay , in a conurbation with the city of Gdynia, spa town of Sopot, and suburban communities, which together form a metropolitan area called the...
. In St. Mary's ChurchSt. Mary's Church, GdanskSt. Mary's Church or, properly, Basilica of the Assumption of the Blessed Virgin Mary is a Roman Catholic church in Gdańsk, Poland, which is the largest brick church in the world. It was begun in 1379. St. Mary's Church (Polish: Bazylika Mariacka, German: Marienkirche) or, properly, Basilica of...
there is an astronomical clock dating from 1464–1470, and built by Hans DüringerHans DüringerHans Düringer was a clockmaker from Nuremberg in Germany who died 1477 in Rostock. His most famous works are the astronomical clocks in St.Mary's Church, Danzig 1470 and St...
of ToruńTorunToruń is an ancient city in northern Poland, on the Vistula River. Its population is more than 205,934 as of June 2009. Toruń is one of the oldest cities in Poland. The medieval old town of Toruń is the birthplace of the astronomer Nicolaus Copernicus....
. It was reconstructed after 1945.
Generic description
Although each astronomical clock is different, they share some common features.Time of day
Most astronomical clocks have a 24 hour analog dial24 hour analog dial
Clocks and watches with a 24-hour analog dial have an hour hand that makes one complete revolution, 360°, in a day...
around the outside edge, numbered from I to XII then from I to XII again. The current time is indicated by a golden ball or a picture of the sun at the end of a pointer. Local noon is usually at the top of the dial, and midnight at the bottom. Minute hands are rarely used.
Altitude
Altitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...
. For azimuth (bearing from North), the top of the dial indicates South, and the two VI points of the dial East and West. For altitude, the top is the zenith and the two VI and VI points define the horizon. (This is for the astronomical clocks designed for use in the northern hemisphere.) This interpretation is most accurate at the equinoxes, of course.
If XII is not at the top of the dial, or if the numbers are Arabic rather than Roman, then the time may be shown in Italian hours
Hour
The hour is a unit of measurement of time. In modern usage, an hour comprises 60 minutes, or 3,600 seconds...
(also called Bohemian, or Old Czech, hours). In this system, 1 o'clock occurs at sunset, and counting continues through the night and into the next afternoon, reaching 24 an hour before sunset.
In the photograph of the Prague clock shown above, the time indicated by the sun hand is about noon (XII in Roman numerals), or about the 17th hour (Italian time in Arabic numerals).
Calendar and zodiac
The year is usually represented by the 12 signs of the zodiacZodiac
In astronomy, the zodiac is a circle of twelve 30° divisions of celestial longitude which are centred upon the ecliptic: the apparent path of the Sun across the celestial sphere over the course of the year...
, arranged either as a concentric circle inside the 24 hour dial, or drawn onto a displaced smaller circle, which is a projection of the ecliptic
Ecliptic
The ecliptic is the plane of the earth's orbit around the sun. In more accurate terms, it is the intersection of the celestial sphere with the ecliptic plane, which is the geometric plane containing the mean orbit of the Earth around the Sun...
, the path of the sun and planets through the sky, and the plane of the Earth's orbit.
The ecliptic plane is projected onto the face of the clock, and, because of the Earth's tilted angle of rotation relative to its orbital plane, it is displaced from the center and appears to be distorted. The projection point for the stereographic projection
Stereographic projection
The stereographic projection, in geometry, is a particular mapping that projects a sphere onto a plane. The projection is defined on the entire sphere, except at one point — the projection point. Where it is defined, the mapping is smooth and bijective. It is conformal, meaning that it...
is the North pole; on astrolabes the South pole is more common.
The ecliptic dial makes one complete revolution in 23 hours 56 minutes (a sidereal
Sidereal
Sidereal, of the stars, may refer to:* Measurements of time:** Sidereal time** Sidereal day** Sidereal month** Sidereal year* Sidereal period of an object orbiting a star* Sidereal astrology...
day), and will therefore gradually get out of phase with the hour hand, drifting slowly further apart during the year.
To find the date, find the place where the hour hand or sun disk intersects the ecliptic dial: this indicates the current star sign, the sun's current location on the ecliptic. The intersection point slowly moves round the ecliptic dial during the year, as the sun moves out of one astrological sign
Astrological sign
Astrological signs represent twelve equal segments or divisions of the zodiac. According to astrology, celestial phenomena reflect or govern human activity on the principle of "as above, so below", so that the twelve signs are held to represent twelve basic personality types or characteristic modes...
into another.
In the photograph of the Prague clock shown above, the sun's disk has recently moved into Aries (the stylized ram's horns), having left Pisces. The date is therefore late March or early April.
If the zodiac signs run around inside the hour hands, either this ring rotates to align itself with the hour hand, or there's another hand, revolving once per year, which points to the sun's current zodiac sign.
Moon
A dial or ring indicating the numbers 1 to 29 or 30 indicates the moon's age: a new moon is 0, waxes and become full around day 15, and then wanes up to 29 or 30. The phase is sometimes shown by a rotating globe or black hemisphere, or a window that reveals part of a wavy black shape beneath.Hour lines
Unequal hours were the result of dividing up the period of daylight into 12 equal hours, and night time into another 12. In Europe, there is more daylight in the summer, and less night, so each of the 12 daylight hours is longer than a night hour. Similarly in winter, daylight hours are shorter, and night hours are longer. These unequal hours are shown by the curved lines radiating from the center. The longer daylight hours in summer can usually be seen at the outer edge of the dial, and the time in unequal hours is read by noting the intersection of the sun hand with the appropriate curved line.Aspects
Astrologers placed importance on how the sun, moon, and planets were arranged and aligned in the sky. If certain planets appeared at the points of a triangle, hexagon, or square, or if they were opposite or next to each other, the appropriate aspectAstrological aspect
In astrology, an aspect is an angle the planets make to each other in the horoscope, and also to the ascendant, midheaven, descendant, lower midheaven, and other points of astrological interest. Aspects are measured by the angular distance in degrees and minutes of ecliptic longitude between two...
was used to determine the event's significance. On some clocks you can see the common aspects—triangle, square, and hexagon—drawn inside the central disk, with each line marked by the symbol for that aspect, and you may also see the signs for conjunction and opposition. On an astrolabe, the corners of the different aspects could be lined up on any of the planets. On a clock, though, the disk containing the aspect lines can't be rotated at will, so they usually show only the aspects of the sun or moon.
In the photograph of the Brescia clock above, the triangle, square, and star in the center of the dial show these aspects (the third, fourth, and sixth phases) of (presumably) the moon.
Dragon hand: eclipse prediction and lunar nodes
The moon's orbit isn't in the same plane as the Earth's orbit around the sun, but crosses it in two places. The moon crosses the ecliptic plane twice a month, once when it goes up above the plane, and again 15 or so days later when it goes back down below the ecliptic. These two locations are the ascending and descending lunar nodes. Solar and lunar eclipses will occur only when the moon is positioned near one of these nodes, because at other times the moon is either too high or too low for an eclipse to be noticed from earth. Some astronomical clocks keep track of the position of the lunar nodes with a long pointer that crosses the dial. This so-called dragon hand makes one complete rotation around the ecliptic dial every 19 years. When the dragon hand and the new moon coincide, the moon is on the same plane as the earth and sun, and so there is every chance that an eclipse will be visible from somewhere on earth.See also
- AstrariumAstrariumAn astrarium, also called a planetarium, is the mechanical representation of the cyclic nature of astronomical objects in one timepiece. It is an astronomical clock.-Greek and Roman World:...
- Armillary sphereArmillary sphereAn armillary sphere is a model of objects in the sky , consisting of a spherical framework of rings, centred on Earth, that represent lines of celestial longitude and latitude and other astronomically important features such as the ecliptic...
- AstrolabeAstrolabeAn astrolabe is an elaborate inclinometer, historically used by astronomers, navigators, and astrologers. Its many uses include locating and predicting the positions of the Sun, Moon, planets, and stars, determining local time given local latitude and longitude, surveying, triangulation, and to...
- OrreryOrreryAn orrery is a mechanical device that illustrates the relative positions and motions of the planets and moons in the Solar System in a heliocentric model. Though the Greeks had working planetaria, the first orrery that was a planetarium of the modern era was produced in 1704, and one was presented...
- PlanetariumPlanetariumA planetarium is a theatre built primarily for presenting educational and entertaining shows about astronomy and the night sky, or for training in celestial navigation...
- TorquetumTorquetumThe torquetum or turquet is a medieval astronomical instrument designed to take and convert measurements made in three sets of coordinates: Horizon, equatorial, and ecliptic...
External links
- The Annosphere, a contemporary astronomical clock
- Les Cadrans Solaires (Sundials), also showing European astronomical clocks
- The horologium, the local astronomic monumental clock from any spot on earth
- THE ASTRONOMICAL CLOCK OF THE ST.-MARIEN-KIRCHE IN ROSTOCK
- MoonlightClock.com -- Handmade Astronomical Clocks