The Prague Astronomical Clock, or Prague Orloj, is a medieval astronomical clock installed on the Old Town Hall tower in 1410. It is the oldest working astronomical clock in the world and one of the key attractions in Prague.

The mechanism in the Prague chimes is incredibly beautiful and complex. It consists of three separate parts: an astronomical dial, a calendar dial, and moving figures. The astronomical dial is the most eye-catching. In the centre, it has the planet Earth, indicating the observer’s position. The dial itself contains lots of interesting and useful information for anyone who can read it. It shows the current, Old Czech, Babylonian and sidereal time, phases of the moon, the rise and set times for the Sun and moon, their position among the constellations of the zodiac circle.

Below the astrolabe, there is the calendar dial, showing the accurate date, day of the week, non-working days, and major holidays of the Christian calendar.

Every day, the figures make an impressive performance which all guests are eager to see. There are eight statues on the right and left of the dials, two on each side. They symbolize human virtues and vices. Many people highlight the frightening image of Death. A few more figures, the twelve apostles, are hidden behind the windows above the astrolabe. Every hour from 9 a.m. to 9 p.m., the figures move and hold a magnificent theatrical show, ending with the crowing of a rooster figure located above.

For many years, the Prague Astronomical Clock was believed to be designed and built by the famous clockmaster Jan Ruze, but it turned out to be a historic mistake. Today, it is known that Prague Orloj was actually made by a Mikulas of Kadan on the draft of the mathematician and astronomer Jan Sindel.

Throughout the whole period of operation, the clock has undergone technical maintenance and repair. Moreover, there is a belief that, if Prague Orloj ever goes wrong, the city will suffer from a serious disaster.