21st Century technology reveals secrets of 2nd Century BC computer


Shipwrecks are the fodder for legend, and the origin of the Antikythera Mechanism, is no exception. Deemed the world’s first computer, this instrument discovered by sponge divers in the ruins of a sunken Roman merchant ship off the Greek island of Antikythera, continues to be the subject of romantic speculation.

Scientists in 1901 originally thought that the antique bronze mechanism was used for calculating and illustrating astronomical data, particularly planetary movements and phases of the Moon. In 2008, members of the Antikythera Research Project were able to reconstruct the gears and their function.

Combining specialized equipment from Hewlett Packard and X-Tek, they examined the mechanism’s 82 remaining fragments. HP used a dome that surrounds an object and takes a series of still photos to analyze the three-dimensional structure of its surface. X-Tek’s 400kV microfocus Computed Tomography (CT) took three-dimensional x-rays, and created images using software from Volume Graphics. All the imaging equipment had to be transported to the National Archaeological Museum in Athens where the artifact is protected from harm or loss.

Antikythera Radiography... three steps to analyze the "world's first computer".
Antikythera Radiography… three steps to analyze the "world’s first computer".

On the picture above, you can see how the computational imaging enabled researchers to find what was this "computer" all about. Up-to-date imaging revealed 752 astronomical inscriptions that had not been discerned in earlier examinations, and they gave credence to the earlier interpretation. The movement of the gears apparently did represent the irregularities of the Moon’s orbit, in a manner theorized by Hipparchos, a Greek astronomer and mathematician who lived circa 190 BC to125 BC. He is credited with founding trigonometry, cataloging the brightness and position of the stars, and accurately modeling the movements of the Sun and Moon. He used a trigonometry table to compute their unique orbits.

The research team also deciphered a 19 year calendar and Corinthian names for the months. This evidence of its cultural origin overturned the previous supposition that the instrument was from the eastern Mediterranean. Speculation runs to Hipparchos having a hand in its invention. Current examinations set the date of the instrument between 150 BC and 100 BC, within the life span of the astronomer.

Antikythera Mechanism Project’s FAQ tell us that the Antikythera Mechanism has 3 main dials. The front dial is marked with divisions of the Egyptian calendar. It probably had three hands marking the date, position of the Sun, and position of the Moon. The Moon indicator is adjusted to show anomalies of the Moon’s orbit. Inside the first dial is a second marked with the Greek signs of the Zodiac. It also can be adjusted – to compensate for leap years.

The number of teeth, 53, in several gears also points towards Hipparchos’ lunar theory. The instrument had at least 30, possibly 37, hand-cut bronze gear-wheels. The clever pin-and-slot device connecting two gear-wheels caused variations in the representation of the Moon’s elliptical orbit around Earth.
Artifacts and texts suggest that much less sophisticated gear driven calendrical devices were used in Baghdad some 1,000 years after the Antikythera Mechanism existed. The complex technology of the earlier instrument was lost near the turn of the millennium to await reinvention in a later age.

Interpretation of the Antikythera Mechanism follows the presumption that all ancient calendars marked the time for planting, harvesting, and celebrating religious events. We are looking to July 2009 when researchers and leading science and technology historians will discuss the implications of the Antikythera Mechanism at the 23rd International Congress of History of Science and Technology to be held in Budapest Hungary.