Astronomical clock
Clocks displaying astronomical information beyond time of day.
Wikipedia / Wikimedia Commons
An astronomical clock, also known as a horologium or orloj, is a clock with special mechanisms and dials to display astronomical information, such as the relative positions of the Sun, Moon, zodiacal constellations, and major planets. The term is loosely used to refer to any clock that shows, in addition to the time of day, astronomical information, including the location of the Sun and Moon in the sky, the age and Lunar phases, the position of the Sun on the ecliptic and the current zodiac sign, sidereal time, and other data such as the Moon's nodes for indicating eclipses or a rotating star map. Astronomical clocks usually represent the Solar System using the geocentric model, with the Earth at the center of the dial.
- field
- Horology, Astronomy
- known_for
- Displaying astronomical information such as positions of Sun, Moon, planets, and zodiac signs
- earliest_known_example
- Antikythera mechanism (2nd century BC)
- notable_early_example
- Su Song's water-driven astronomical clock (11th century, Song dynasty China)
- notable_medieval_examples
- Richard of Wallingford's clock (1330s), Giovanni Dondi dell'Orologio's clock (1348–1364)
Lore & Background
The Antikythera mechanism, dating from the 2nd century BC, is the oldest known analog computer and a precursor to astronomical clocks. It used complex gears to determine positions of the sun, moon, and planets, predict eclipses, and track Olympic Games. Research in 2011 and 2012 suggested that European astronomical clocks are descended from its technology. In the 11th century, Song dynasty Chinese horologist Su Song created a water-driven astronomical clock for his clock-tower in Kaifeng City, incorporating an escapement mechanism and the earliest known endless power-transmitting chain drive. Contemporary Muslim astronomers and engineers also built highly accurate astronomical clocks for observatories, such as Ibn al-Shatir's astrolabic clock in the early 14th century.
Reader's Guide
Astronomical clocks were built as demonstration or exhibition pieces intended to impress as well as to educate or inform. The challenge of building them allowed clockmakers to demonstrate technical skill and their patrons' wealth. Their philosophical message of an ordered, heavenly-ordained universe, which accorded with the Gothic-era view of the world, explains their popularity. The growing interest in astronomy during the 18th century revived interest in astronomical clocks, less for the philosophical message and more for the accurate astronomical information that pendulum-regulated clocks could display. Most astronomical clocks have a 24-hour analog dial, with the Sun indicated by a golden ball or image. They often include a zodiac dial, a moon phase indicator showing the Moon's age from 0 to 29 or 30, and curved lines for unequal hours. The ecliptic dial makes one revolution in a sidereal day (23 hours 56 minutes), and the date is found where the hour hand or Sun disk intersects it. Astronomical clocks vary in design but share these common features, and the term should not be confused with an astronomical regulator, a high-precision pendulum clock used in observatories.
Did You Know?
- The Antikythera mechanism from the 2nd century BC is the oldest known analog computer and a precursor to astronomical clocks.
- Su Song's 11th-century water-driven astronomical clock incorporated the earliest known endless power-transmitting chain drive.
- Richard of Wallingford's 1330s clock may have shown the sun, moon, stars, planets, a wheel of fortune, and the tide at London Bridge.
- Most astronomical clocks use the geocentric model, with the Earth at the center of the dial.
Frequently Asked Questions
What exactly is an astronomical clock?
It is a timekeeping device that goes well beyond simply marking the hour, using gears and dials to track celestial bodies such as the Sun, Moon, planets, and zodiac constellations in real time.
Who created the famous Chinese astronomical clock?
The Song dynasty polymath Su Song designed and built a water-powered astronomical clock tower in 1088, which became one of the most sophisticated mechanical devices of its era.
What specific information did Su Song's clock display?
It tracked the positions of the Sun and Moon, showed lunar phases, indicated the current zodiac sign, and featured a rotating armillary sphere that modeled the night sky for observers.
How does the Chinese astronomical clock compare to earlier examples like the Antikythera mechanism?
While the ancient Greek Antikythera mechanism from the 2nd century BC predates it, Su Song's 11th-century tower was far more complex, combining a water-driven escapement with multiple simultaneous astronomical and calendrical displays in a single structure.
Why does the Chinese astronomical clock matter in the broader history of science?
It proved that pre-modern Chinese engineers had independently developed precision gearwork and escapement mechanisms centuries before comparable European clocks appeared in the 1300s, making it a landmark achievement in both horology and early observational astronomy.
More in Chinese inventions 1-24
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