Astronomical Clocks: A Fascinating History of Timekeeping and Astronomy

An astronomical clock is a type of clock that displays astronomical information, such as the positions of the sun, moon, planets, and stars. These clocks have been used since ancient times to keep track of time and the movements of celestial bodies. They were developed to help astronomers and astrologers to make accurate predictions about celestial events and to aid in navigation.

Astronomical clocks come in a variety of forms, from simple sundials to complex mechanical devices with multiple dials and moving parts. Some of the most famous astronomical clocks are found in European cities, such as Prague, Strasbourg, and Bern.

The Prague astronomical clock, also known as the Orloj, is one of the oldest and most famous astronomical clocks in the world. It was built in the early 15th century and is located on the Old Town Hall in Prague. The clock features an astronomical dial, which displays the positions of the sun, moon, and stars, as well as a calendar dial and a display of the phases of the moon.

The Strasbourg astronomical clock is another famous example of an astronomical clock. It was built in the late 16th century and is located in the Strasbourg Cathedral. The clock features a number of dials and displays, including an astronomical dial, a perpetual calendar, and a display of the phases of the moon.

Astronomical clocks are not just decorative pieces; they serve practical purposes as well. For example, sailors used astronomical clocks to help them navigate the seas by using the position of the stars to determine their location. They were also used by astronomers to make accurate observations of celestial events, such as eclipses and planetary conjunctions.

History of Astronomical Clocks

The history of astronomical clocks dates back to ancient times when humans first began to observe the stars and planets in the sky. The earliest known example of an astronomical clock is the Antikythera mechanism, a complex mechanical device that was discovered in 1901 in the Antikythera shipwreck off the coast of Greece. The mechanism, which is believed to have been built in ancient Greece between 150 and 100 BCE, displayed the phases of the moon, the position of the sun and moon, and the movements of the five known planets.

Over the centuries, astronomical clocks became more common and were built in various forms, from simple sundials to complex mechanical devices with multiple dials and moving parts. During the Middle Ages, they were used primarily for religious purposes, such as to mark the times for prayer and to determine the dates of religious festivals.

One of the earliest recorded astronomical clocks in Europe was built in the 11th century by the Islamic scholar Al-Jazari. The clock was installed in the Palace of the Caliph in Baghdad and displayed the positions of the sun, moon, and stars.

In Europe, the first mechanical clocks were developed in the 13th century and gradually became more complex over time. Astronomical clocks began to be built into the clock towers of churches and other public buildings, such as town halls. These clocks typically featured an astronomical dial, which displayed the positions of the sun, moon, and stars, as well as other features, such as a calendar dial and a display of the phases of the moon.

One of the most famous astronomical clocks in Europe is the Prague astronomical clock, also known as the Orloj. It was built in the early 15th century and is located on the Old Town Hall in Prague. The clock features an astronomical dial, which displays the positions of the sun, moon, and stars, as well as a calendar dial and a display of the phases of the moon.

During the Renaissance, astronomical clocks became even more elaborate and were often used as symbols of wealth and power by kings and princes. One of the most impressive examples of a Renaissance astronomical clock is the Strasbourg astronomical clock, which was built in the late 16th century and is located in the Strasbourg Cathedral. The clock features a number of dials and displays, including an astronomical dial, a perpetual calendar, and a display of the phases of the moon.

In the modern era, astronomical clocks have been largely replaced by more accurate and precise timekeeping devices, such as atomic clocks. However, they continue to be popular tourist attractions and are a testament to the ingenuity and creativity of human beings throughout history.

The Prague Astronomical clock

The Prague astronomical clock, also known as the Orloj, is a medieval astronomical clock located in the Old Town Square in Prague, Czech Republic. It is one of the oldest and most elaborate astronomical clocks in the world, and is a popular tourist attraction.

The clock was built in the early 15th century by the clockmaker Mikuláš of Kadaň, and was later modified and expanded by other clockmakers over the centuries. The clock consists of three main components: the astronomical dial, the calendar dial, and the automata.

The astronomical dial is the main feature of the clock and displays the position of the sun, moon, and stars. It consists of a circular dial with a moving background that represents the Earth’s rotation, along with an outer ring that displays the 24-hour astronomical time. The sun is represented by a golden hand that moves around the dial, while the moon is represented by a silver hand.

The calendar dial is located below the astronomical dial and displays the current day of the month, the month, and the zodiac signs. It also includes an hourly indication of the time in normal hours and a lunar calendar.

The automata consist of several figures that move when the clock strikes the hour. The most famous of these figures is the “Procession of the Apostles,” which features twelve apostles moving past the windows above the astronomical dial.

The clock has undergone several restorations over the centuries, the most recent of which was completed in 2020. The restoration work included cleaning and repairing the clock’s intricate mechanisms and replacing the aging wooden panels with new ones made from linden wood.

Today, the Prague astronomical clock remains a symbol of Prague’s rich history and cultural heritage. It attracts millions of visitors each year who come to marvel at its beauty and complexity, and to witness the striking of the hour and the movement of the automata.

The Strasbourg Astronomical clock

The Strasbourg astronomical clock is a large, elaborate clock located in the cathedral of Notre Dame in Strasbourg, France. It was constructed in the 16th century by several clockmakers, including Isaac Habrecht and his son, Josuah Habrecht.

The clock is over 18 meters tall and consists of several dials, calendars, and automata. It is considered one of the most complex and impressive astronomical clocks in the world.

The main dial of the clock displays the time, as well as the position of the sun and moon in the sky. It also shows the signs of the zodiac and the phases of the moon. Above the dial is a figure of Atlas, holding a globe that rotates once a day.

The lower part of the clock features a calendar with the months, the signs of the zodiac, and the days of the week. It also includes an indication of the date according to the Julian and Gregorian calendars.

One of the most notable features of the Strasbourg astronomical clock is its automata, which include several figures that move when the clock strikes the hour. The most famous of these is a rooster that crows three times and flaps its wings. The automata also include figures of apostles and allegorical figures that move and perform various actions.

The Strasbourg astronomical clock has undergone several restorations over the centuries, the most recent of which was completed in 2019. The restoration work included cleaning and repairing the clock’s mechanisms and automata, as well as restoring the original colors of the clock’s case and sculptures.

Today, the Strasbourg astronomical clock remains an important cultural and historical artifact, as well as a popular tourist attraction. It is considered a masterpiece of Renaissance clockmaking and a testament to the ingenuity and skill of the clockmakers of the past.

Mechanics of Astronomical Clocks

Astronomical clocks are complex timepieces that incorporate a wide range of mechanical and astronomical components. The key components of an astronomical clock include:

• The escapement: This is the mechanism that controls the movement of the clock’s gears and ensures that the clock ticks at a regular interval. The escapement consists of a pendulum or balance wheel that swings back and forth, along with an anchor or pallets that control the motion of the gear train.

• The gear train: This is the series of gears that transmit the motion of the escapement to the clock’s hands and other components. The gear train also includes various ratios that determine the speed at which the hands move around the clock face.
• The dial: This is the face of the clock that displays the time and astronomical information. The dial can include a wide range of features, from simple hour and minute hands to complex astronomical displays.
• The astronomical components: These are the various mechanisms that display astronomical information, such as the position of the Sun, Moon, and planets. These components can include:
• The astrolabe: This is a two-dimensional representation of the celestial sphere that shows the position of the Sun and stars relative to the Earth. The astrolabe was a common component of medieval astronomical clocks and was used to determine the time of day and the date of the year.
• The moon phase indicator: This is a rotating disk that displays the phases of the Moon. The disk is usually divided into two halves, one light and one dark, that represent the illuminated and unilluminated portions of the Moon.
• The planetarium: This is a rotating mechanism that displays the positions of the planets relative to the Earth. The planetarium can include models of the planets that move around the dial, or a system of gears and disks that accurately calculate the positions of the planets based on their orbits.
• The calendar: This is a mechanism that displays the day, month, and year. The calendar can be a simple disk with the months and days of the year, or a more complex mechanism that includes information about the zodiac, the phases of the Moon, and the dates of equinoxes and solstices.

Astronomical clocks can be incredibly complex and require a high level of skill to build and maintain. Many of the clocks that have survived to this day are considered to be works of art as well as functional timepieces, and they continue to amaze and inspire people with their intricate designs and fascinating astronomical features.

Modern Times & The Future of Astronomical Clocks

Astronomical clocks have a rich history that spans several centuries and are considered marvels of engineering and craftsmanship. In modern times, these clocks have been replaced by more accurate and precise timekeeping devices, such as atomic clocks, which use the vibrations of atoms to keep time. These devices are far more accurate than mechanical clocks, as they do not rely on pendulums or balance wheels that can be affected by changes in temperature and humidity.

Despite this, astronomical clocks continue to hold a place of significance in history and remain popular tourist attractions in many cities around the world. They are seen as a symbol of the ingenuity and creativity of past civilizations and are admired for their beauty and complexity.

In recent years, there has been a renewed interest in astronomical clocks, and several new clocks have been constructed. These new clocks incorporate modern technology and materials, such as LED lighting and carbon fiber, while still maintaining the traditional design and function of astronomical clocks.

One example of a modern astronomical clock is the Corpus Clock, which was unveiled in Cambridge, England in 2008. The clock features a unique design that incorporates a large, intricate sculpture of a grasshopper on top of the clock face, which moves back and forth to mark the seconds.

Another example is the Cosmic Time Clock, which was installed in 2018 at the University of Edinburgh in Scotland. The clock features a digital display that shows the position of the planets in the solar system and the current time in various locations around the world.

As technology continues to advance, it is likely that astronomical clocks will continue to evolve and incorporate new features and materials. However, they will always remain an important part of human history and a testament to our fascination with the movements of the celestial bodies above us.