What is the Orloj?
The third-oldest astronomical clock in the world and oldest working example is the Orloj in Prague, Czech Republic. Installed in the southern wall of the Old Town Square in 1410, the oldest parts of the Orloj clock are over 600 years old, although it’s been repaired numerous times over the centuries, especially at the end of WWII.
Early astronomical clocks, like Su Sung’s 11th-century Cosmic Engine, were regulated by a wheel turned by falling water, but later examples – including the Prague Orloj – were also reliant on Earth’s gravity for movement, via the action of weights, pulleys and levers. The Orloj’s design has been improved a number of times over the generations.
The many facets of the Orloj give it 20 different functions in addition to simply telling the time, including keeping track of the tropics, measuring ancient Czech time and monitoring solar and lunar movements.