Discovered by Greek sponge divers in 1901, artifacts recovered from a Roman shipwreck included a lump of corroded bronze and wood. Gears were discovered inside its cracked mass, but not until 70 years later was this artifact interpreted as an astronomical computer. Recent studies have far superseded past work. X-ray tomography has revealed a gears and workmanship like that inside a wristwatch. High-tech surface image techniques have allowed scientists to read many more inscribed characters on the exterior, apparently amounting to the user’s manual. 

A virtual reconstruction has recently been published in the scientific literature (a replica has been made for a London museum), and the original resides on display in Athens. Named after the island near its discovery, the Antikythera Mechanism, is an incredible anomaly. No earlier geared mechanism is known, and nothing approaching its technology appeared for the next thousand years. The virtual renderings are astonishing and have to be seen to be believed.

About the size of a shoebox, the front had two concentric dials, one representing the Zodiac, the other the days of the year. By turning a knob, tiny balls showing the position of the Sun and Moon and pointers for the five known planets all moved in accurate relative motion. Two spiral dials adorned the backside of the box. The top dial showed the Callippic Cycle (four Metonic cycles less one day), and the bottom dial represented the Saros cycle of eclipses. Inside, over 30 gears drove the solar system through its orbital motions.  By far the cleverest aspect of the mechanism appears in two wheels, one atop another engaged by a slot with a pin on the lower wheel. Since they are not centered, the top wheel moves faster or slower depending on the position of the pin. Mechanically, this pin-and-slot arrangement mimicked changes in speed as the Moon orbits the Earth elliptically, precisely as described by the famous Greek astronomer Hipparchus.

Based on geographic location and other shipwreck artifacts, the origin of the mechanism can be determined with some certainty: vases from the trading port of Rhodes were part of the cargo. Rhodes was the center of astronomical science in the first and second centuries BC, and Hipparchus studied on Rhodes until his death about 120 BC. Recovered coins date the shipwreck to shortly after 85 BC, and given the apparent novelty and sophistication pin-in-slot mechanism, it is very possible that this device may have been inspired or even used by Hipparchus himself.

The Antikythera Mechanism is an analog computer, something that has all but disappeared in the digital age of the Internet and web. A plansiphere or star wheel is an analog astronomical computer, and a slide rule is an analog numerical calculator, but neither is anywhere as sophisticated as the Antikythera Mechanism. As impressive as it seems today, its power must have seemed astonishing to people long ago. Perhaps rather than designed for mere computation, as the Greek’s equivalent of the World Wide Web, the Mechanism was itself a representation of the beauty of the heavens.

Moondark is written by Doug Miller, published at the Moondark web site, and printed in the Delmarva Star Gazers' Star Gazer News. This document was last revised on 1 January 2007. Text and images copyright © 2007 by Douglas C. Miller, All Rights Reserved. This material may not be reproduced in any form without prior permission.