An early astronomical computer

At the beginning of the 20th century, divers made a chance find of a shipwreck from the first century BC near the Greek island of Antikythera. One object they discovered among the wreckage has turned out to be perhaps the earliest example of an astronomical computer ever found.

The device consists of a box with dials on the outside and a complex assembly of gear wheels mounted inside. Following much conservation work, it is now in the Greek National Archaeological Museum in Athens.

In appearance, the device gives an impression rather like that of an 18th century clock. At least 20 of the mechanism’s gear wheels have been preserved, and there may well have been others that are now lost. On the surfaces of the box, the doors and the dials there are inscriptions in Greek describing the operation and construction of the instrument.

A paper published in the journal Nature in 2006 describes current thinking on the purpose of the device. A team led by Mike Edmunds, of Cardiff University, has been working on the device using x-rays and other technologies such as computed tomography.

They have concluded that it was most probably a computer to predict solar and lunar eclipses from the relative positions of the sun, the moon and the earth.

In an interview about the instrument, Professor Edmunds said: “The real significance of this is just how sophisticated the device was  —much more complex than a modern wristwatch. It is beautifully designed and must have come from a long tradition of making these kinds of devices.”

Such a complex device is unlikely to have been built in isolation, so others may be awaiting discovery by archaeologists. We may therefore have to rewrite the history both of astronomy and of the construction and use of mechanical computers.