The Antikythera celestial calculator

Exceptional

The 82 recovered fragments. The three main fragments are displayed at the National Archaeological Museum in Athens. © 2006 Antikythera Mechanism Research Project

Fragment A (front), one of the three fragments displayed in the Bronze Collection. © 2006 Antikythera Mechanism Research Project

Fragment A (back). © 2006 Antikythera Mechanism Research Project

Fragment B (front), with surviving inscriptions. © 2006 Antikythera Mechanism Research Project

Fragment B (back). This fragment would have been at the back of the mechanism. © 2006 Antikythera Mechanism Research Project

Reconstruction: Callipic calendar and Saros cycle for calculating eclipses (back); Egyptian calendar and zodiac, motions of the moon and sun (front). © 2006 Antikythera Mechanism Research Project

Reconstructed gear-wheel (back and front). © 2006 Antikythera Mechanism Research Project

The complexity of this device, discovered under the Aegean Sea and whose functioning and purpose are only now coming to light, is quite simply astounding. It resembles a clockwork mechanism but is in fact based on Babylonian arithmetic-progression cycles.

Gian Pozzy

"If the Ancient Greeks had been as perspicacious as they were ingenious, the industrial revolution would have begun a thousand years before Christopher Columbus," wrote Arthur C. Clarke. The author, in 1968, of 2001: A Space Odyssey was alluding to the Antikythera mechanism, a bizarre geared construction, the size of a book and weighing a few hundred grams, that has fascinated the scientific community ever since it was brought up from the bottom of the Aegean Sea in 1900. This bronze and wood mechanism, constructed towards the end of the second century BC, was almost certainly used to calculate the positions of the sun, moon and possibly other planets too and, more importantly, to predict eclipses with surprising precision. Blaise Pascal, inventor in 1641 of the Pascaline arithmetic machine, has been credited with the first mechanical calculator. In reality, the Greeks got there eighteen centuries before him.

References by Cicero

Archaeologists, astronomers, historians and physicists were unable to fathom this mysterious object. Everyone knew the Greeks were past masters in intuition and conjecture, but who would have imagined they were technical wizards too? The Antikythera mechanism is alone in the world, having no known ancestor or descendant… or possibly not, as Cicero makes reference to two similar constructions. One was brought to Rome by General Marcellus, following the capture of Syracuse in 212 BC. Attributed to Archimedes, it remained in the general’s family for 150 years before the celebrated senator saw and wrote about it in De Re Publica (I.22).

According to Cicero then, this type of calculator already existed in the third century BC. In De Natura Deorum (II.88), he refers to another similar object, built by his friend and mentor Posidonius, a Stoic philosopher, physicist and meteorologist. How could such technically sophisticated objects appear out of nowhere to then vanish without leaving any other trace? The mystery remains intact.

Unravelling the mystery

The Antikythera mechanism began its second life in 1900 when Elias Stadiatos, a sponge diver, came across a ship 42 metres under the Aegean Sea. The wreck was later dated to 86 or 87 BC. The marble and bronze statues, pottery, glassware, jewellery and coins that filled its hold suggested this was a Roman galley returning from the sacking of Pergamon in Asia Minor (now Izmir). Among these many treasures was some kind of shapeless wooden box, which went unheeded until May 17th, 1902 when the archaeologist Valerios Stais noticed the bronze gears embedded in it.

Scientific investigators a century ago lacked the resources to make out the structure under the crust of solidified silt that encased it. A further 50 years went by before British and Greek scientists were able to clean the mechanism by electrolytic deoxidation and analyse it using X-rays and gamma-rays. They uncovered an arrangement of dials, shafts, cylinders and hands that bore a remarkable similarity to the first astronomical clocks of the Renaissance. The British science historian Derek de Solla Price saw in it a device for calculating the motions of the stars and planets. However, he was forced to end his investigations there for want of more sophisticated resources.

An astoundingly complex mechanism

The mechanism held on to its secrets until 2000, when the Welsh astronomer Mike Edmunds decided to scan its fragments. As no suitable device existed, an eight-ton prototype 3D-imaging scanner had to be made, generating images to within 50 microns. Professor Edmunds and his team discovered that this strange machine, which had languished 2,000 years under the sea, comprised some twenty gear-wheels and was covered in Greek inscriptions, over 2,000 characters in all, believed to constitute a user’s guide and a basic astronomical treatise. This astoundingly complex mechanism resembles clockwork; it is in fact based on Babylonian arithmetic-progression cycles.

Two concentric circles form a dial on one side of the mechanism. One circle is graduated into 360 parts representing the Greek zodiac. The other is divided into the 365 days of the Egyptian calendar. The inner surface is inscribed with an astronomical calendar. Two other dials, both with subsidiary dials, form a spiral on the mechanism’s other side. These are engraved with numbers: 19 for the Metonic cycle (the 235 lunations after which the full and new moons will appear on the same day of the solar year), 76 for the more accurate Callipic cycle of four x 19 years, and 223 for the Saros cycle, corresponding to the number of lunar months between two eclipses of the sun and moon.

An ingenious device

The Antikythera mechanism rose from the bottom of the sea to challenge our assumption that the Ancient Greeks were loath to venture away from theory and actually construct objects, and for this reason it continues to fascinate the scientific community. However, we mustn’t lose sight of the fact that it is based on a geocentric concept of the universe, as put forward by Hipparchus in the second century BC (and which continued right until Copernicus and Galileo), when already in the third century BC a certain Aristarchus of Samos had imagined a vast universe in which "the earth revolves about the sun in the circumference of a circle, the sun lying in the middle of the orbit," as quoted by Archimedes. Who would have thought it of the Ancient Greeks! ■

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