The Prague Astronomical Clock (Orloj) is an astronomical clock system located in Prague, the capital of the Czech Republic, and is considered among the rarest works of medieval engineering. It is a multifunctional instrument that does not only show the concept of time in hours and minutes, but also reflects the positions of the Sun, Moon, and celestial bodies. At first glance, its dial system, which appears complex, aims to depict the celestial dome and the arrangement of constellations. The mechanical arrangement on the front of the clock provides extensive information about the astronomy of its era. Located at Old Town Square (Staroměstské náměstí), this clock is regarded as one of the city’s most important tourist landmarks due to its historical structure and artistic embellishments.

^{Prague Astronomical Clock (Photo: Wolfgang Weiser, unsplash.com)}

History

Its construction dates back to the first half of the 15th century, that is, the late Middle Ages. According to common belief, clockmaker Mikuláš z Kadaně (Nikolas of Kadaň) and astronomer Jan Šindel contributed to the initial design and manufacturing stages. Toward the end of the 15th century, rings reflecting Zodiac signs and different time divisions of the day were added to the clock’s dial. In the same period, animated figures and statues were installed, turning the clock from being merely an astronomical instrument into one also endowed with artistic elements. Throughout the 16th and 17th centuries, maintenance and repair activities continued intensively, and clockmakers made renewals to the mechanism. Especially the restoration works carried out in 1865 and 1866 largely shaped the clock’s current appearance.

During World War II, severe damage occurred, seriously harming parts of the clock and especially its wooden figures. As a result of the comprehensive restorations initiated after the war, the clock regained its original functionality and its cultural value was preserved. ^【1】  Thanks to the technical possibilities developed in the late 20th and early 21st centuries, both the mechanism and the external ornaments were revisited; modern maintenance methods were applied with priority given to preserving the historical texture.

Working System

The Prague Astronomical Clock has a complex arrangement consisting of three main parts:

Astronomical Dial (Main Display)

This dial, which contains the Sun, Moon, and Zodiac symbols, reflects the positions of celestial bodies in addition to the classical time display. On the outer ring, the sunrise and sunset times are shown in different colors, while the rotating disk in the middle indicates the hour of the day.

Clock Mechanism

The mechanism is a traditional arrangement based on gears and weight systems. When the clock spring is wound at set intervals, it updates the information on the dial by rotating the hands through the movement of weights and gears. Having survived since the Middle Ages thanks to various maintenance and restoration efforts, this structure continues to enchant the city’s tourists and residents with a short animation at every hour.

Animation and the Hour Strikes

At the top of every hour, a movement of figures called the “Procession of the Twelve Apostles” is observed through two windows. At the same time, the skeleton figure on the clock emphasizes the inevitability of death by shaking the hourglass in its hand. Symbols like mirrors and money bags reflect common social fears and themes of the Middle Ages, such as vanity and greed.

^{Close-up view of the Prague Astronomical Clock (Photo: Falco, pixabay.com)}

Figures Around the Clock

The figures of the Prague Astronomical Clock are important for symbolizing the beliefs and values of Medieval Europe. Around the clock, there are four main figures, each reflecting different themes and period beliefs. These figures come to life at every hour, symbolizing four different elements that were negatively perceived in that era.

The first figure is vanity, gazing at itself in a mirror. Right next to it is another figure holding a bag of gold, representing greed or usury. Directly opposite is a skeleton (Death) who rings a small bell at every hour, reminding of the end of life. The final figure is a character depicted as the symbol of lust and worldly pleasures in the Middle Ages. When the skeleton rings the bell, the other three figures shake their heads from side to side, indicating they are not yet ready to “go.”

In addition, at every hour of the day, small doors on the upper part of the Astronomical Clock open, and the statues of the Twelve Apostles appear in sequence with their distinctive characteristics. In this procession, Lesser James and Peter, Andrew and Matthias, Thaddeus and Philip, Thomas and Paul, John and Simon, Barnabas and Bartholomew appear in order. Comparing this list with that of the canonical gospels, the inclusion of Paul and Barnabas instead of Greater James and Matthew shows that the arrangement used in the clock differs from the classic apostolic sequence.

^{The figures of the Prague Astronomical Clock (Photo: Xiquinho Silva, flickr.com)}

Calendar

The calendar section located at the bottom of the Prague Astronomical Clock displays the traditional Gregorian calendar. This circularly designed calendar disk shows the months and days of the year in detail. In addition to the months, it also indicates the dates of relevant saints or religious days. Using Zodiac symbols, it marks the horoscopes of that period.

The calendar disk sheds light on Prague’s cultural and religious calendar traditions from past to present. Since the Zodiac system has been a frequently used set of symbols for the public understanding of astronomy since ancient times, the calendar on the clock also emphasizes astrological details.^【2】 

^{The calendar of the Prague Astronomical Clock (Photo: PublicDomainPictures, pixabay.com)}