The clock mechanism has three main components – the astronomical dial, representing the position of the Sun and Moon in the sky and displaying various astronomical details; statues of various Catholic saints stand on either side of the clock; "The Walk of the Apostles", an hourly show of moving Apostle figures and other sculptures, notably a figure of a skeleton that represents Death, striking the time; and a calendar dial with medallions representing the months.

[1] The oldest part of the Orloj, the mechanical clock and astronomical dial, dates back to 1410, when it was created by horologist Mikuláš of Kadaň and Charles University professor of mathematics and astronomy Jan Šindel.

Formerly, it was believed that the Orloj was constructed in 1490 by clockmaster Jan Růže (also called Hanuš); this is now known to be a historical mistake.

A legend, recounted by Alois Jirásek, has it that the clockmaker Hanuš was blinded on the order of the Prague Councillors so that he could not repeat his work; in turn, he disabled the clock, and no one was able to repair it for the next hundred years.

The hall and nearby buildings burned, along with the wooden sculptures on the clock and the calendar dial face made by Josef Mánes.

[4] After significant effort, the machinery was repaired, the wooden Apostles restored by Vojtěch Sucharda, and the Orloj started working again in 1948.

The video interacted with the tower's architecture, such as rain rolling off the arch, and showing the passage of time with moving shadows.

[12][13] The artwork on the Orloj became the center of controversy after a local heritage group noticed the reproduction had "radically changed the appearance, ages, skin tone, dress and even genders of the figures" illustrated by Mánes in 1866.

[14] A member of the Club for Old Prague, Milan Patka, registered a complaint with the Ministry of Culture, alleging that in the restoration, painter Stanislav Jirčík had deviated from the "spirit and detail" of the original.

Alternatively, one may consider the Orloj to be a primitive planetarium, displaying the current orientation of the universe relative to the Earth.

These hours are defined as 1/12 of the time between sunrise and sunset, and vary as the days grow longer or shorter during the year.

The Moon has a 57-tooth gear inside its sphere, and is slowly rotated by a screw-thread attached to a weight, advancing two teeth per day.

This movement, powered only by gravity, makes the Orloj unique in the world among astronomical clocks showing the phases of the Moon.

Unlike the original device, the construction of which was described in a report from 1570, this mechanism produces much smaller deviation from the actual lunar phase of about one day in five years.

The left and right windows above the astronomical clock slide aside to reveal the Apostles as viewed from the square in this order: James the Less and Peter, Andrew and Matthias, Thaddeus and Philip, Thomas and Paul, John and Simon, Barnabas and Bartholomew.

Unlike the list of the Twelve Apostles mentioned in the canonical gospels, James the Great and Matthew are missing, replaced by Paul and Barnabas.

Next to the calendar stands a philosopher, archangel Michael pointing at the top of the dial, an astronomer and a chronicler.