The astronomical clock of Prague (Orloj in Czech) has been measuring time for six centuries. According to available sources, its mechanical astrolab, a wonder of medieval engineering, was put into action on October 9, 1410.

Prague Orloj became an iconic landmark of the city and a cherished piece of the world cultural heritage. It is known to display several types of time, as well as positions of celestial bodies and other interesting data.

After having watched the famous walk of 12 apostles at the end of  each hour, many visitors leave with only a limited understanding of Orloj’s dials, curves, and numbers. It is because our lives pass much faster than when the Orloj was built. Movements of the Orloj’s parts are so slow from our perspective that they are almost unnoticeable.

Orloj has no minute hand, because more time precision than an hour was not important. People believed that the Earth was right in the center of the Universe. An hour during the summer was twice as long as during the winter. A day would last from one sunset to the next one, a concept that would not be practical today. The date derived from the Zodiac ring has a precision that is not better than days.

Our iPhone model will help you understand movements of this fascinating instrument. You’ll be able to take, in the palm of your hand, the Orloj for a spin. Enter a date, and the Orloj will move its components into a new position. Step forward in time by an hour, minute, day, month, or a year, and watch the animation. Enter for instance your day of birth to see the phase of the Moon when you were born. Observe how the Sun moves between the tropics. All this and more can be decoded from the model.