Welcome to the Prague Astronomical Clock
Find your way to the astronomical clock. Our website can be your guide.
The Prague Astronomical Clock, or else the Old Town Astronomical Clock, is one of the most renown and most visited tourist attractions in the historical centre of Prague. It is a medieval astronomical clock mounted on the southern wall of the Old Town City Hall in Prague (GPS: 50 05 16.59 N, 14 25 14.489 E). Although the clock was seriously damaged several times in the past, it was always repaired with the aim of preserving the technical, artistic and spiritual integrity to the maximum extent possible. At present, it is probably the best preserved medieval astronomical clock in the world. The entire astronomical clock, indicators, chiming system, bells and movements of the apostles and sculptures is controlled by mainly original ironwork machine, whose foundation was built in 1410 by Mikuláš of Kadaň. Since the great renovation in 1866, it has also been controlled by the mechanical chronometer by Romuald Božek.
The most dominating part of the astronomical clock is the astronomical dial, constructed as an astrolabe with projection from the celestial northern pole. This dial is very frequently presented as one of the main symbols of Prague. It has been copied at many places in our country as well as all over the world.
The Sun arm with a golden hand attached to it shows three various times on the astronomical dial: common civil time, Old Czech Time, and Babylonian time. The oldest one, which is not used today, is the time in unequal hours, called Babylonian hours (or, for their astrological meaning, planetary hours). The Babylonian time is read approximately at the place where the golden Sun is located, or rather in the intersection of the Sun arm and the ecliptic on the fingery lines. The time between the sunrise and sunset was divided into 12 equal portions, whose duration changes in the course of the year. The contemporary common civil time divides the day into 2x12 equally long hours starting at midnight and at noon. The time of the old Czech (Italian) clock also divides the day into 24 equal hours counted from the sunset. It is indicated on the outward rotated dial – the 24‑hour ring. The golden star connected to the ecliptic ring indicates the sidereal time, which is counted from the moment of passing of the vernal point over the local meridian.
The Golden Sun indicates the current position of the Sun both in the sky and within the zodiac, the Moon sphere then shows, beside the position of the Moon in the sky and within the zodiac, also its position towards the Sun and its phase, which is the visible portion of its sunlit hemisphere.
The calendar dial makes one turn per year. It is installed on the astronomical clock since 1490 and its contemporary form is from 1866. On the perimeter of the dial, days in the year, names of saints, dominical letter and a syllable from the Cisiojanus is indicated. J. Mánes decorated the dial with scenes from rural life, which symbolize individual months. He also depicted the Sun Signs in an unconventional way. Mánes’s work was replaced by a copy due to apprehension that it would be damaged by weather conditions.
On the astronomical clock, a plentiful sculptural decoration draws attention. The lining of the astrolabe is probably work of Petr Parléř’s stoneworks, other stonework and sculptural decoration dates back to the end of the 15th century and is in Late Gothic style.
The most appreciated touristic attraction is the defile of the 12 wooden sculptures of the Apostles in the upper windows of the astronomical clock and the movements of some other wooden sculptures, which decorate the clock and which remind us of the frailty of human life (the Death) or various human qualities (e. g. Vanity). They are set in motion by the clock’s machines every hour between 9 am and 9 pm CET. The performance is concluded by a cockcrow.