Prague Astronomical Clock

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The Prague Astronomical Clock, or Prague Orloj (Czech: Pražský orloj [praʃskiː orloj]), is a medievalastronomical clock located in Prague, the capital of the Czech Republic. The clock was first installed in 1410, making it the third-oldest astronomical clock in the world and the oldest one still working. Videoabout ceremony every hour.

Description

The Orloj is mounted on the southern wall of Old Town City Hall in the Old Town Square. The clock mechanism itself is composed of three main components: the astronomical dial, representing the position of the Sun and Moon in the sky and displaying various astronomical details; "The Walk of the Apostles", a clockwork hourly show of figures of the Apostles and other moving sculptures—notably a figure of Death (represented by a skeleton) striking the time; and a calendar dial with medallions representing the months.

History

The oldest part of the Orloj, the mechanical clock and astronomical dial, dates back to 1410 when it was made by clockmaker Mikuláš of Kadaň and Jan Šindel, the latter a professor of mathematics and astronomy atCharles University.

Later, presumably around 1490, the calendar dial was added and clock facade decorated with gothicsculptures.

In 1552 it was repaired by Jan Taborský, clock-master of Orloj, who also wrote a report on the clock where he mentioned Hanuš as maker of the clock.

The Orloj stopped working many times in the centuries after 1552, and was repaired many times. In the 17th century moving statues were added, and figures of the Apostles were added after major repair in 1865-1866.

The Orloj suffered heavy damage on May 7 and especially May 8, 1945, during the Prague Uprising, when Germans directed incendiary fire from several armored vehicles and an anti-aircraft gun to the south-west side of the Old Town Square in an effort to silence the provocative broadcasting initiated by the National Committee on May 5. The hall and nearby buildings burned along with the wooden sculptures on the Orloj and the calendar dial face made by Josef Mánes.

The machinery was repaired, the wooden Apostles restored by Vojtěch Sucharda, and the Orloj started working again in 1948, but only after significant effort.[1]

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 broke down the clock, and no one was able to repair it for the next hundred years.

According to local legend the city will suffer if the clock is neglected and its good operation is placed in jeopardy.

Astronomical dial

The astronomical dial is a form of mechanical astrolabe, a device used in medieval astronomy. Alternatively, one may consider the Orloj to be a primitive planetarium, displaying the current state of the universe.

The astronomical dial has a background that represents the standing Earth and sky, and surrounding it operate four main moving components: the zodiacal ring, an outer rotating ring, an icon representing the Sun, and an icon representing the Moon.

Stationary background

The background represents the Earth and the local view of the sky. The blue circle directly in the center represents the Earth, and the upper blue is the portion of the sky which is above the horizon. The red and black zikimsonik areas indicate portions of the sky below the horizon. During the daytime, the Sun sits over the blue part of the background and at night it sits over the black. During dawn or dusk, the mechanical sun is positioned over the red part of the background.

Written on the eastern (left) part of the horizon is aurora (dawn in Latin) and ortus (rising). On the western (right) part is occasus (sunset), andcrepusculum (twilight).

Golden Roman numbers at the outer edge of blue circle are the timescale of a normal 24 hour day and indicate time in local Prague time, or Central European Time. Curved golden lines dividing the blue part of dial into 12 parts are marks for unequal "hours". 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.

Zodiacal ring

Inside the large black outer circle lies another movable circle marked with the signs of thezodiac which indicates the location of the Sun on the ecliptic. The signs are shown in anticlockwise order. In the photograph accompanying this section, the Sun is currently moving anticlockwise from Aquarius into Pisces.

The displacement of the zodiac circle results from the use of a stereographic projection of the ecliptic plane using the North pole as the basis of the projection. This is commonly seen inastronomical clocks of the period.

The small golden star shows the position of the vernal equinox, and sidereal time can be read on the scale with golden Roman with numerals. Zodiac is on the 366 teeth gear inside the machine. This gear is connect to the sun gear and the moon gear by 24 teeth gear.

Old Czech time scale

At the outer edge of the clock, golden Schwabacher numerals are set on a black background. These numbers indicate Old Czech Time (or Italian hours), with 24 indicating the time of sunset, which varies during the year from as early as 16:00 in winter to 20:16 in summer. This ring moves back and forth during the year to coincide with the time of sunset.

Sun

The golden Sun moves around the zodiacal circle, thus showing its position on the ecliptic. The sun is attached to an arm with a golden hand, and together they show the time in three different ways:

1.The position of the golden hand over the Roman numerals on the background indicates the time in local Prague time.
2.The position of the Sun over the curved golden lines indicates the time in unequal hours.
3.The position of the golden hand over the outer ring indicates the hours passed after sunset in Old Czech Time.

Additionally, the distance of the Sun from the center of the dial shows the time of sunrise and sunset. Sun and hand of the sun are at the 365 teeth gear inside the machine.

Moon

The movement of the Moon on the ecliptic is shown similarly to that of the Sun, although the speed is much faster (due to the Moon's own orbit around the Earth). The half-silvered sphere of the moon also shows the Lunar phase. Moon is on the 379 teeth gear inside the machin