five kinds of time on one clock 

The astronomic clock on the old town hall of Prague consists of three parts:

1. At the top, behind two shutters, a kind of puppet show from the 19th century showing at each hour the figures of the twelve apostles.

2. At the foot in a circular calendar, pictures of  the months and seasons and for each day the saint of the day.

3. In the middle
, the oldest and most ingenious part, a multiple clock from 1410.

At the square near the clock each hour hunderds of tourists come together. The walking apostles attract their full attention. This spectacle takes less than one minute. About the clock itself they get mostly no information.

According to legend the maker of the clock in Prague, finishing his work, was made blind to prevent him to make a similar clock in an other town.

Photo (2007) Willy Leenders
The clock as a whole
The clock indicates five kinds of time:

- the Central European Time;

- the time, measured in a division of twelve 'hours', between sunrise and sunset, the unequal or temporal hours.  From day to day they are longer or shorter because the period between
sunrise and sunset varies each day;

the time, measured in a division of 24 hours indicating the time untill sunset (sunset = 24), the Bohemian or Italian hours;

- the position of the sun in the zodiac;

- the sidereal time.

Even the position of the moon is indicated. In the drawings hereto this is not depicted.

The clock consists of 
the stationary disk in the center and two independently rotating disks, the outer ring with numerals in Gothic style and the zodiacal ring.

There are three pointers: the hand with the little real hand, the little sun moving back and forth 
on this hand and the hand with the asterisk wich is connected to the zodiacal ring.

Drawing (2008) Willy Leenders

Animated picture: the clock on the 10th of each month at 9:30 a.m.

Animated picture (2008) Willy Leenders
Local solar time and unequal hours on the central disk
At the central disk the hand indicates Central European Timerepresented by Roman numerals. At the drawing hereto the little hand indicates about 2:20 p.m..

Between the curved golden lines the
little sun indicates the time advanced between sunrise and sunset in a distribution of 12 hours, represented in Arabic numerals, known as the 'unequal hours' (in winter  short hours - at the inner circle - and in summer long hours - at the outer circle). At the drawing hereto: the end of the nineth hour.

The little sun is situated always at the edge of the zodiacal ring and therefore moves up and down on the hand. The central golden circle indicates the place where the little sun is located at the beginnning of spring  and autumn; day and night are then equally long.

At the start of the day ORTUS (sunrise)
is mentioned, at the end OCASUS (sunset). The period before sunrise is indicated as AURORA (dawn), the period after sunset as CREPUSCULUM (twilight).

Drawing (2008) Willy Leenders

The clock would have to indicate the local solar time as before.
It was originally set to mean solar time and from time tot time it was manually adjusted to correct the Equation of Time.

In 1912, it was set to indicate Central European Time (C.E.T.)
In 1957, the indication of the Bohemian time is adjusted accordingly.
The hour lines of unequal hours are fixed and can not be adjusted. That indication is actually wrong.
Because Prague (14 ° 25 'E) is  near the 15-degree meridian line, the reference for Central European Time, the difference between C.E.T. and the local solar time is about two minutes plus a correction equal to the Equation of Time.
In February and early November, the total difference is on its maximum: about a quarter of an hour.
Then the clock, respectively, gains about a quarter of an hour and is about a quarter of an hour slow with regard to local solar time.
Bohemian or Italian hours on the outer ring
On the outer ring, the hand with the little real hand indicates the Bohemian hours (also known as Italian hours). This kind of time was used in the Middle Ages in Bohemia, the country to which Prague belonged, and in Nord Italy.

The time of day plus night is divided in 24 hours. At sunset the hand indicates 24.

At the drawing hereto the hand indicates 22, thus 2 hours before sunset.

To get this result the outer ring
with the numerals rotates during one half of the year (when the days becomes longer) slowly to the right and in the other half (when the days becomes shorter) to the left. The time indicated at the top at noon varies from 15:55 (still 8:05 hour to sunset) to 20:05 (still 3.55 tot sunset).

The numerals are in Gothic style.

is 7

Drawing (2008) Willy Leenders
On the zodiacal ring: the position of the sun in the zodiac and the sidereal time
On the zodiacal ring the little sun indicates the place of the sun in the zodiac. At the drawing hereto: the transition from Water bearer to Fishes, approximately at frebruar 18.

The zodiacal ring is placed excentrically in the clock. It rotates once
in a year around its own centre and on its own in one day around the centre of the clock. During this combined motion the little sun remains on the border of the zodiacal ring and on the hand.

An asterisk is connected to the zodiacal ring, lengthening the dividing line between
Fishes and Ram (the vernal point). It indicates the sidereal time, to be read on the scale with Roman numerals.
At the first drawing hereto approximately 00:20.

Drawing (2008) Willy Leenders
The clock programmed in a spreadsheet. Click here
In this spreadsheet (Excel) you can 'construct' the clock for each place in the world (except between the pole circles and the poles) on each moment of the year.