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Orloj - Astronomical Clock - Prague
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© Christine Till - CT-Graphics
The Astronomical Clock in Prague (Pražský orloj), built in 1410, is divided in three parts. Displayed here is the astronomical dial, constructed as an astrolabe with projection from the celestial northern pole.
On both sides of the clock dial is a pair of moving statues. In medieval times they were seen as the four menacing elements for the city of Prague. The figures have moving parts, set in motion by the clock’s machines, although they themselves remain where they stand. On the left: The Vain/Vanity (admiring himself in a mirror), and The Miser/Jew (holding onto his bag of gold). On the right: Death (rings the bell), and A Turk - also called The Piper.
The Clock continually provides the full range of astronomical data. The dial shows three mutually independent movements: the mean revolutions of the Sun, the mean revolutions of the Moon and the apparent revolutions of the stars (the ecliptic, to be more precise). The horizon is indicated by the boundary of blue and red; in the left part the day-break (AVRORA) with a rising border (ORTVS), in the right part the twilight (CREPVSCVLVM) with a setting border (OCCASVS). The dark circle at the bottom displays the astronomical night. Three pointers rotate around this dial: one for the Sun, one for the Moon and the third is for zodiac.
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 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 shows, beside the position of the Moon in the sky and within the zodiac, 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.
At present, the Orloj in Prague is probably the best preserved medieval astronomical clock in the world. You can tell ... I'm facinated.
April 13th, 2012
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