Astronomical Clock: History and Features

Astronomical Clock: History and Features

of reading - words

By definition, an astronomical clock is a clock that displays astronomical information in addition to the time. This astronomical data can be related to the location of the sun and the moon, some examples :

  • the current phase of the moon in the lunar cycle.
  • the location of the sun relative to the ecliptic.
  • the zodiacal climate showing the months of the year.

1) History and creation of the astronomical clock

1) Who invented the astronomical clock?

In the history of watchmaking, Richard of Wallingford is known to have developed an astronomical clock in the 1330's. An English mathematician, he contributed a great deal to watchmaking in addition to astronomy and astrology, as these three elements were closely linked at the time. He was also a believer and served as abbot in the Abbey of St Alban. Giovanni de Dondi was also credited with developing an astronomical clock in Padua between 1348 and 1364.

Both men developed clocks that were considered masterpieces of the time, unfortunately none of these astronomical clocks still exist today. Fortunately, the details of their design and construction have been recorded, which has been of great use to future generations. Nowadays, modern replicas of these two clocks ahead of their time have been created.

2) The first astronomical clocks

Features of Richard's clock include information about the position of the sun, the lunar cycle, the planets and stars, and a wheel of fortune. The clock also features a tide gauge to track the tide of the Thames. The design of Giovanni's clock is a little more complex. Called the Astrarium, the clock has a seven-sided construction with one hundred and seven moving parts. This version of the astronomical clock displays the different positions of the sun and the moon, as well as five of the planets in the solar system. It also notes certain religious holidays. 

On the left is a reproduction of Richard's clock and on the right is Giovanni's Astrarium:

3) Limitations of these clocks

Due to the large scale of both designs and the limitations of the technology of the time, these early astronomical clock forms were not as accurate as desired at the time of construction. They could therefore not be used reliably to track the time and the stars. Their primary function was to be used for demonstration purposes in order to impress technical skills and wealth. In the 18th century, the population became increasingly interested in astronomy, so the astronomical clock became more and more desired and present in the culture. Advanced technology allowed for greater precision and clocks were used as intended for astronomical calculations.

2) Characteristics of a standard astronomical clock

Each astronomical clock is unique to its designer (like our Scandinavian clocks), but there are a few features they all share.

1) Time display

To begin with, astronomical clocks show the time with a dial representing the 24 hours of the day. Using Roman numerals, the clock reflects the time from I to XII on the two ellipses of the semicircle, with noon at the top and midnight at the bottom. The left side of the clock therefore represents night and morning, while the right side represents afternoon and evening. The astronomical clock rotates like all other clocks, from left to right. A golden ball or representation of the sun indicates the time at the end of the hand.

2) Signs of the zodiac

To represent the year, astronomical clocks use the signs of the zodiac indicating their respective months. The signs of the zodiac are usually displayed inside the time dial. To represent the Earth's inclined rotation on the orbital plane, the clock shows a projection of its off-centre movement in this area of the clock. The dial extends from the elliptical projection and is used to track the movement of the earth around the sun. This dial operates at sidereal time, and thus marks a full day of twenty-three hours and fifty-six minutes. As a result of the following sidereal time, the elliptical hand will slowly desynchronize with the hour hand.

3) Moon time

Astronomical clocks also show the age of the moon on a ring ranging from one to thirty years. When the moon is new, it rests at zero, grows to about fifteen and weakens when it reaches the number twenty-nine or thirty. Clocks also have unequal time lines. These time lines represent the differences between summer and winter time in terms of the amount of daylight. Since daylight saving time changes with the seasons, astronomical clocks note this with the help of curved lines. Another common hand on the astrological clock is the dragon hand. About every nineteen years or so, the dragon hand makes a complete rotation around the ecliptic dial, which means that the dragon hand, the new moon, the earth and the sun are all in the same plane. When this happens, an eclipse will be visible from the earth.

3) The most beautiful astronomical clocks around the world

1) Astronomical Clock in Prague (Czech Republic)

One of the most famous astronomical clocks in Prague is located in the Old Town Hall. The Prague Orloj, as it is called, dates back to 1410 and features religious representations as well as standard structures. Since its creation, the clock has undergone several renovations to ensure that it is still working. According to local superstition, when the clock stops working, the city of Prague will experience great misfortune.

2) The Olomouc Astronomical Clock (Czech Republic)

Another town in the Czech Republic is home to a famous astronomical clock. A very rare heliocentric clock, which shows the sun as the centre of the universe, was displayed on the village square in Olomouc. Built in 1422, the clock was renovated every hundred years. During the Second World War, the Nazi army damaged the clock, leaving behind fragments which are now on display in the Olomouc Museum. A reconstruction of the original clock was ordered with modifications replacing religious figures in favour of members of the proletariat.

3) The astronomical clock of Beauvais (France)

There is an astronomical clock inside the cathedral in Beauvais, France. Built over four years, starting in 1865, this clock has more than ninety thousand pieces of work, with fifty-two dials. In addition to the time, the clock displays the lunar phases, solstices and tide times. It also features a celestial city that shows the final judgment hour by hour. 

4) The Astronomical Clock in Copenhagen (Denmark)

Copenhagen, Denmark, is home to an astronomical clock that took fifty years to design. Initial construction began in 1948 and was completed in 1955. The clock is housed in a glass cabinet in the City Hall. Jens Olsen, a clockmaker by trade and an astronomer by hobby, was the brain behind the clock.

4) Replica to install at home

If you've reached the end of this article it's because you're really interested in astronomical clocks. If you would like to install one in your home feel free to have a look at our wooden astronomical wall clock that faithfully respects the Prague astronomical clock.

The Master of Time