The mysterious Antikythera mechanism—an ancient device believed to have been used for tracking the heavens—has fascinated scientists and the public alike since it was first recovered from a shipwreck over a century ago. Much progress has been made in recent years to reconstruct the surviving fragments and learn more about how the mechanism might have been used. And now, members of a team of Greek researchers believe they have pinpointed the start date for the Antikythera mechanism, according to a preprint posted to the physics arXiv repository. Knowing that "day zero" is critical to ensuring the accuracy of the device.
“Any measuring system, from a thermometer to the Antikythera mechanism, needs a calibration in order to [perform] its calculations correctly,” co-author Aristeidis Voulgaris of the Thessaloniki Directorate of Culture and Tourism in Greece told New Scientist. “Of course it wouldn’t have been perfect—it’s not a digital computer, it’s gears—but it would have been very good at predicting solar and lunar eclipses.”
As we've previously reported, in 1900, a Greek sponge diver named Elias Stadiatis discovered the wreck of an ancient cargo ship off the coast of Antikythera island in Greece. He and other divers recovered all kinds of artifacts from the ship. A year later, an archaeologist named Valerios Stais was studying what he thought was a piece of rock recovered from the shipwreck when he noticed that there was a gear wheel embedded in it. It turned out to be an ancient mechanical device. The Antikythera mechanism is now housed in the National Archaeological Museum of Athens.
In 1951, a British science historian named Derek J. de Solla Price began investigating the theoretical workings of the device. Based on X-ray and gamma ray photographs of the fragments, Price and physicist Charalambos Karakalos published a 70-page paper in 1959 in the Transactions of the American Philosophical Society. Based on those images, they hypothesized that the mechanism had been used to calculate the motions of stars and planets—making it the first known analog computer.
In 2002, Michael Wright, then curator of mechanical engineering at the Science Museum in London, made headlines with new, more detailed X-ray images of the device taken via linear tomography. Wright's closer analysis revealed a fixed central gear in the mechanism's main wheel, around which other moving gears could rotate. He concluded that the device was specifically designed to model "epicyclic" motion in keeping with the ancient Greek notion that celestial bodies moved in circular patterns, called epicycles. (This was pre-Copernicus, so the fixed point around which they moved was believed to be the Earth.)
Last year, an interdisciplinary team at University College London (UCL) led by mechanical engineer Tony Freeth made global headlines with their computational model, revealing a dazzling display of the ancient Greek cosmos. The team is currently building a replica mechanism, moving gears and all, using modern machinery. The display is described in the inscriptions on the mechanism's back cover, featuring planets moving on concentric rings with marker beads as indicators. X-rays of the front cover accurately represent the cycles of Venus and Saturn—462 and 442 years, respectively.
The team's efforts built on Wright's work as part of the ongoing Antikythera Mechanism Research Project, which undertook more advanced 3D X-ray imaging with the help of X-Tek Systems in the UK and Hewlett-Packard, among others. The new images revealed much more of the original Greek transcription, which was subsequently translated. High-resolution X-ray tomography confirmed it was an astronomical computer used to predict the positions of heavenly bodies in the sky. It's likely that the Antikythera mechanism once had 37 gears, of which 30 survive, and its front face had graduations showing the solar cycle and the zodiac, along with pointers to indicate the positions of the Sun and Moon.
The Antikythera mechanism was likely built sometime between 200 BCE and 60 BCE. However, in February 2022, Freeth suggested that the famous Greek mathematician and inventor Archimedes (sometimes referred to as the Leonardo da Vinci of antiquity) may have actually designed the mechanism, even if he didn't personally build it. (Archimedes died in 212 BCE at the hands of a Roman soldier during the siege of Syracuse.) There are references in the writings of Cicero (106-43 BCE) to a device built by Archimedes for tracking the movement of the Sun, Moon, and five planets; it was a prized possession of the Roman general Marcus Claudius Marcellus. According to Freeth, that description is remarkably similar to the Antikythera mechanism, suggesting it was not a one-of-a-kind device.
Voulgaris and his co-authors based their new analysis on a 223-month cycle called a Saros, represented by a spiral inset on the back of the device. The cycle covers the time it takes for the Sun, Moon, and Earth to return to their same positions and includes associated solar and lunar eclipses. Given our current knowledge about how the device likely functioned, as well as the inscriptions, the team believed the start date would coincide with an annular solar eclipse.
In such an event, the Sun and Moon are precisely aligned with Earth, such that the Moon appears smaller and only covers the Sun's center, leaving the Sun's visible outer edges to form a “ring of fire." An annular eclipse in which the Moon was at the furthest point from Earth in its orbit (the apogee) would have been of particularly long duration. So Voulgaris and his cohorts searched NASA's database to find all the examples of such events falling within the time period the Antikythera mechanism was likely built.
Only the Saros series 58 included long annular eclipses. The longest occurred on December 23, 178 BCE. "Usually, in order to perform time calculations, it is more common to select a date from the recent past than one in the future, especially during ancient times, when time calculations and predictions for a large time span were more uncertain and doubtful than today," the authors wrote. "This fact could also be the most probable reason for the construction of the Antikythera mechanism in that era."
As further evidence, Voulgaris et al. cite several other culturally significant astronomical events that would have occurred around the same time. One is the annual winter solstice, helpfully engraved on the front top left of the mechanism. Voulgaris et al. believe that's a strong indication that the solstice was involved in the calibration. Another is the religious festival Isia, marking the assassination of Osiris and tied to lunar and solar eclipses. There would have been a visible solar eclipse at sunrise on December 22, 178 BCE, per the authors, a rare occurrence and hence likely to hold significance for priests of that period.
“This is a very specific and unique date,” Voulgaris said. “In one day, there occurred too many astronomical events for it to be coincidence. This date was a new moon, the new moon was at apogee, there was a solar eclipse, the Sun entered into the constellation Capricorn, it was the winter solstice.”
Others have made independent calculations and arrived at a different conclusion: the calibration date would more likely fall sometime in the summer of 204 BCE, although Voulgaris countered that this doesn't explain why the winter solstice is engraved so prominently on the device.
“The eclipse predictions on the [device’s back] contain enough astronomical information to demonstrate conclusively that the 18-year series of lunar and solar eclipse predictions started in 204 BCE,” Alexander Jones of New York University told New Scientist, adding that there have been four independent calculations of this. “The reason such a dating is possible is because the Saros period is not a highly accurate equation of lunar and solar periodicities, so every time you push forward by 223 lunar months… the quality of the prediction degrades.”
