The Antikythera mechanism is a multi-component device recovered from a shipwreck close to the Greek island of Antikythera in 1901. It is believed to be the remains of a complex mechanical calculator of ancient origin, and has undergone considerable investigation and analysis to determine its true form and function. In new research, astronomers from the University of Glasgow used statistical modeling techniques developed to analyze gravitational waves to establish the positions of holes beneath the calendar ring of the Antikythera mechanism. Their results provide fresh evidence that this component was most likely used to track the Greek lunar year.
A fragment of the Antikythera mechanism. Imager credit: National Archaeological Museum, Athens / CC BY-SA 3.0.
The Antikythera wreck is a Roman-era shipwreck dating from the first century BCE (85-50 BCE).
It is located on the east side of the Greek island of Antikythera near Crete at the crossroads of the Aegean and Mediterranean Seas.
The Antikythera ship is thought to have been carrying looted treasures from the coast of Asia Minor to Rome, to support a triumphal parade being planned for Julius Caesar.
The wreck was discovered in 1900 by a group of Greek sponge divers on their way to Tunisia who took shelter from a storm near the island and decided to look for sponges while they waited for calmer conditions.
Early excavations at the site revealed a wealth of discoveries that today are housed in the National Archaeological Museum in Athens, Greece. These included three life-size marble horses, jewelry, coins, glassware, and hundreds of works of art, including a statue of Herakles.
The most surprising discovery was the corroded remnants of a complex device known as Antikythera mechanism, which is believed to be an early analog computer used to plan important events including religious rituals, the early Olympic Games, and agricultural activities.
Sometimes described as the first mechanical computer, the bronze device was constructed during the period 150-100 BCE.
It was originally housed in a wooden-framed case of overall size 31.5x19x10 cm and had front and back doors, with astronomical inscriptions covering much of the exterior.
Its remaining fragments contain 30 gears in a highly complex arrangement. Technological artifacts of similar complexity did not appear until 1,000 years later.
In 2020, new X-ray images of one of the mechanism’s rings, known as the calendar ring, revealed fresh details of regularly spaced holes that sit beneath the ring.
Since the ring was broken and incomplete, however, it wasn’t clear how just how many holes were there originally.
An initial analysis by Antikythera researcher Chris Budiselic and colleagues suggested it was likely somewhere between 347 and 367.
Top: 82 surviving fragments of the Antikythera Mechanism. Image credit: T. Freeth et al, 2006. Bottom: reconstruction of the Antikythera Mechanism by Allan Bromley and Frank Percival. Image credit: Allan Bromley.
In the new study, University of Glasgow researchers Graham Woan and Joseph Bayley used two statistical analysis techniques to reveal new details about the calendar ring.
They show that the ring is vastly more likely to have had 354 holes, corresponding to the lunar calendar, than 365 holes, which would have followed the Egyptian calendar.
The analysis also shows that 354 holes is hundreds of times more probable than a 360-hole ring, which previous research had suggested as a possible count.
“Towards the end of last year, a colleague pointed to me to data acquired by YouTuber Chris Budiselic, who was looking to make a replica of the calendar ring and was investigating ways to determine just how many holes it contained,” Professor Woan said.
“It struck me as an interesting problem, and one that I thought I might be able to solve in a different way during the Christmas holidays, so I set about using some statistical techniques to answer the question.”
Professor Woan used a technique called Bayesian analysis, which uses probability to quantify uncertainty based on incomplete data, to calculate the likely number of holes in the mechanism using the positions of the surviving holes and the placement of the ring’s surviving six fragments.
His results showed strong evidence that the mechanism’s calendar ring contained either 354 or 355 holes.
At the same time, Dr. Bayley had also heard about the problem. He adapted techniques used by their research group to analyze the signals picked up by the LIGO gravitational wave detectors, which measure the tiny ripples in spacetime, caused by massive astronomical events like the collision of black holes, as they pass through the Earth, to scrutinise the calendar ring.
The Markov Chain Monte Carlo and nested sampling methods Professor Woan and Dr. Bayley used provided a comprehensive probabilistic set of results, again suggested that the ring most likely contained 354 or 355 holes in a circle of radius 77.1 mm, with an uncertainty of about 1/3 mm.
It also reveals that the holes were precisely positioned with extraordinary accuracy, with an average radial variation of just 0.028 mm between each hole.
“Previous studies had suggested that the calendar ring was likely to have tracked the lunar calendar, but the dual techniques we’ve applied in this piece of work greatly increase the likelihood that this was the case,” Dr. Bayley said.
“It’s given me a new appreciation for the Antikythera mechanism and the work and care that Greek craftspeople put into making it — the precision of the holes’ positioning would have required highly accurate measurement techniques and an incredibly steady hand to punch them.”
“It’s a neat symmetry that we’ve adapted techniques we use to study the universe today to understand more about a mechanism that helped people keep track of the heavens nearly two millennia ago,” Professor Woan said.
“We hope that our findings about the Antikythera mechanism, although less supernaturally spectacular than those made by Indiana Jones, will help deepen our understanding of how this remarkable device was made and used by the Greeks.”
A paper on the findings was published in the July 2024 issue of The Horological Journal.
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Graham Woan & Joseph Bayley. 2024. An Improved Calendar Ring Hole-Count for the Antikythera Mechanism: A Fresh Analysis. The Horological Journal
This article was adapted from an original release by the University of Glasgow.
