The Prague Astronomical clock, the Orloj, was constructed in 1410 by Mikuláš of Kadaň and Jan Šindel, professor of mathematics at Prague University. A calendar below the clock and more ornate decoration was added in the 1490s. More figures appeared in the 17th century and the final major element, the parade of Apostles above the clock, was added in the 19th century.
Carved wooden figures of the Apostles were added to the Astronomical Clock during a refurbishment in 1865 and 1866. The 19th century figures were lost when German forces burned down the Old Town Hall on the last day of the Second World War; the figures that parade today were carved after the war by Vojtech Sucharda.
Every hour during the day the wooden shutters on the small windows open inwards and a set of six carved figures appears in sequence at each window. When all twelve Apostles have gone past their windows, there's a sound a bit like a rooster crowing and the windows slam shut. At this point the watching tourists either cheer or applaud.
The following pairs of pictures show the pairs of Apostles that appear the left and right windows simultaneously. We've identified the Apostles by what they're carrying, which might not be the most reliable method.
First pair of Apostles:
On the left, Saint James the Lesser with his pilgrim staff;
On the right, Saint Peter with the keys of heaven.
Second pair of Apostles:
On the left, Saint Andrew carrying a St. Andrew's cross;
On the right, Saint Matthias carrying an axe.
Third pair of Apostles:
On the left, Saint Matthew with a purse;
On the right, Saint Philip with a cross.
Fourth pair of Apostles:
On the left, Saint Thomas holding a lance;
On the right, Saint James the Greater with a book and a sword.
Fifth pair of Apostles:
On the left, Saint John carrying a chalice with a snake in it;
On the right, Saint Simon holds the saw he was cut in half with.
Sixth and final pair of Apostles:
On the left, Saint Thaddeus carrying the robes of Jesus;
On the right, Saint Bartholomew carrying the knife he was skinned with.
The background shows a blue circle for the Earth, with the sky above the horizon shown in blue and the sky below the horizon in red or black. A inner ring marked with zodiacal symbols moves around the circle, rotating once a sideral day; a pointer bearing a hand and a sun rotates once a solar day; a second pointer moves slightly faster to show the moon. The outer ring moves forward and back depending on the time of year.
Figures on either side of the clock face, added in the 17th century:
On the left, Vanity admiring himself in a mirror, and Greed (portrayed as a Jew) clutching a bag of gold;
On the right, Death waving a bell and an hourglass and a Turk shaking his head.
The golden hand indicates the hour of the day. Against the Gothic numerals of the outer ring it indicates the number of hours since sunset. Against the inner circle of Roman numerals it indicates the local time in Prague. The Roman numerals were presumably added as an afterthought as at times (for instance when these pictures were taken) they are obscured by the zodiac disc.
The sun moves around the zodiac circle, showing its postion on the ecliptic. Read against the curved lines (marked with Arabic numerals) it shows the time since sunrise in unequal hours.
The star shows sideral time.
The moon indicator has essentially the same movement as the sun, but with the addition of a turning motion which simulates the phase of the moon; one side of the moon is black so that it can appear to wax and wane.
The outer ring indicates the time in Old Bohemian (or Italian) hours, using a 24 hour day starting at sunset. The ring is numbered from 1 to 24 in an ornate Gothic script (in which the 4 resembles a fish standing on its tail), and moves forward and back during the year. The numeral 24 matched against the Roman numerals shows the time of sunset in Prague; this picture was taken in mid-June, when sunset was about 8pm.
Sideral time : time measured by the apparent daily motion of the stars.
Unequal hours : dividing the day into 12 'hours' between sunrise and sunset. The first hour begins at sunrise, the sixth ends at midday and the twelth ends at sunset. The length of each hour depends on the amount of daylight.
The current calendar was painted by Josef Manes in 1805. The disc moves every day, turning anti-clockwise. The figures to the left and right are stationary.
Figures on either side of the calendar:
On the left, a Chronicler and an Angel brandishing a sword (the sword looks like a big feather, but is probably intended to be flaming);
On the right, an Astronomer and a Philosopher.
The calendar disc revolves throughout the year, with the date indicated by the little arrow at the top of the carved circle. Exactly how useful this is, given the size of the text defining the day and the fact that the arrow is as far from any viewer as possible, is rather questionable.
The month is indicated by a pair of zodiac related painted roundels. In astrology Taurus runs from April 20 to May 21; in astronomy Taurus runs from May 13 to June 21 and this is an astronomical clock, so the picture on the left, taken on June 12, 2008, shows the day as being in Taurus.
Each roundel has a representation of agricultural work relevant to the time of year, with a smaller representation of appropriate constellation below it.
The gate with three towers in the centre of the disc is a simplification of the coat of arms of Prague; there should really be an arm waving a silver sword in the gateway.