The elliptical movement of the Moon and its simulation by the Mechanism

The Antikythera Mechanism is the oldest existing complex geared device, an amazing geared analogue computer. It was built approximately 2150 years ago and was used to calculate astronomical phenomena.

The device was operated manually by a user, to set a date on a dial and notice the astronomical phenomena that occur on that day. Respectively, by choosing an astronomical phenomenon he can observe at which date it will happen.  All necessary calculations were made using a set of gears (at least 39).

The Mechanism was used to calculate the diurnal and annual motion of the Sun, the Moon and probably the planets among the stars. It calculated the position of the Sun and the Moon on the Sky and the phases of the Moon for every day of the year and predict eclipses of the Sun and the Moon.

It implemented the astronomical knowledge of ancient Greeks about the motion of these heavenly bodies with astonishing accuracy, considering the anomalous motion of the Moon around the Earth, using a system of eccentric gears.

Essentially, in the Antikythera Mechanism, the epicyclic theory of Hipparchus is integrated. This theory was formulated to interpret the retrograde motions of the planets as well as the change in the angular velocity of the rotation of the moon around the Earth. Today we know that the moon’s anomalous motion is due to its elliptical orbit as it turned around the Earth (Kepler’s laws). It could, also, predict eclipses of the Sun and the Moon.

In addition, the Mechanism calculated the celebration date of the ancient Panhellenic Games. On the circumference of a corresponding dial found on the fragments of the Mechanism, the words Olympia, Pythia, Isthmia, Nemea and Naa have been deciphered. Internally, in each quadrant, the four years of the Olympic cycle are indicated. All these games were crowned Games, with winners being rewarded with olive wreaths.

The Antikythera Mechanism was a complicated instrument. Therefore, it is not surprising that it was accompanied by an extensive User’s Manual. New inscriptions that had not been read for more than 2000 years were revealed, mainly with the X-ray micro-focusing tomography. About 3500 letters and symbols have been deciphered up to now.


The collection is dedicated to Ioannis Seiradakis, whose contribution was a catalyst for the inception of the research for the Antikythera Mechanism, in 2005, which led to its decoding.

John H. Seiradakis (5 March 1948 – 3 May 2020)