The Prague Orloj (Prague Astronomical Clock) is part of the Old Town Hall and you will see it on the left as you enter the Old Town Square on Staromestkke nam. Built in the 14th Century by a clockmaker known as Hanus, the Prague Astronomical Clock is the oldest working medieval clock in the world !
The clock is made up of 3 intricate parts.
Astronomical Dial – The astronomical dial shows three different times; common civil time Old Czech time and Babylonian time. The outer most dial has Arabic characters showing Old Bohemian time (Old Czech time). Inside of that there are Roman numerals showing time as we know it. And the blue part of the dial shows Babylonian time. It is divided into 12 parts because in those days, the Babylonians divided their days into 12 daylight hours which varied according to the time of year.
The Twelve Apostles – Now this is the interesting bit. Gather outside the clock tower 10 – 15 minutes before the hour. No doubt there will be hoardes of tourists there already before you. Anyway find a nice spot and get your camera or video camera ready as it’s quite amusing. The skeleton you see there on the right will pull a rope which he holds and ring a bell. The blue doors above will open and a procession of the 12 Apostles will begin. At the end of it, a cock crows and the clock chimes x number of times depending on what hour it is.
Calendar Dial – Finally there is the calendar dial which was mounted some years later. It displays the signs of the zodiac and tells the day and month of the year !
This clock tells you just about everything related to time. However, as it wasn’t meant to tell the exact time but to display the orbits of the sun and moon around the Earth, I wouldn’t suggest you try to use it to see if you’re going to be on time for your flight!