TWH – At first, archaeologists thought of the Antikythera Mechanism as mere debris from a shipwreck. Now, they describe it as an analog computer from the Hellenistic Age. That age lasted from the death of Alexander in 323 B.C.E. to the death of Cleopatra in 30 B.C.E. People built that analog computer before astronomy had that ugly divorce from astrology.
The mechanism has now entered the realm of pop culture. In 2010, it became part of the world of LEGO objects. In 2017 on May 17, it became the Google Doodle. In 2023, it became part of the Indiana Jones franchise with “Indiana Jones and the Dial of Destiny.”
Two recent studies, however, have challenged a key interpretation of how it worked.
The Challenge
Scientists had accepted that the mechanism measured a solar year of roughly 365 days. Earlier this year, Graham Woan and Joseph Baley of the University of Glasgow published a report challenging that belief. In that report, they found that the mechanism measured a lunar year of roughly 354 days. A prior article in the Horological Journal had reached similar conclusions.
History of the Mechanism
The Proceedings of the American Philosophical Society reported that in 1900, sponge divers discovered a shipwreck. The ship had sunk in the waters between mainland Greece and the island of Crete. Soon, an archaeological salvage operation began. It is unclear when the salvage team first brought the mechanism to the surface. Scientists failed to notice it until 1902. At first, they described it as “two ‘slabs’ of corroded metal.” Those slabs tended to blend in with the other unidentified scraps of bronze from the wreck. Scientists noticed two things in the fragments. They could see toothed gear wheels and inscribed Greek letters. In the early 1900s, scientists concentrated on dating its manufacture.
Over the Twentieth Century, they began to realize that functioned as a computer. It calculated planetary positions, eclipses, and dates for the Olympic games. Rather than using semiconductors to calculate, it used gears.
For the mechanically challenged, a gear is a circular object that rotates. It has a series of alternating peaks (“teeth”) and valleys. One gear is usually paired with another gear (“a gear train”). A gear train can transmit speed or force in an economical way. In a gear train of unequal-sized gears, one gear drives another. A gear train of unequal-sized gears either amplifies or decreases speed or force.
The New York Times reported that the shipwreck occurred between 85 and 60 B.C.E. Scientists have proposed dates for the construction of the mechanism ranging from 205 B.C.E. to 87 B.C.E. This range places it firmly in the Hellenistic Age. The Antikythera Mechanism has upended the contemporary understanding of Hellenistic science and technology.
In the Hellenistic Age, massive cultural and intellectual exchanges occurred among Egypt, Greece, and Mesopotamia. Neither the beginning nor the end of the Hellenistic Age occurred in Greece. Alexander died in Babylon. Cleopatra died in Alexandria. Babylonian astronomy/astrology and the Egyptian calendar influenced the mechanism. As did the calligraphy, language, and cosmos of the Greeks. The cosmos described in the mechanism matches the Cosmos of the ancient Greeks. This mix of cultures and technologies produced the mechanism.
Mechanism of Antikythera, 150-100 BC. National Archaeological Museum of Athens. [Image Credit: ZDE CC ASA 4.0]
Models of how the mechanism functioned
The mechanism shows corrosion, fragmentation, and other damage. Enough of it remains to make inferences about how it would have worked. Enough also remains to make functional models. Some models, like the LEGO model, belong to the world of infotainment. Other models have more scientific value.
In Scientific Reports, Freeth et al described the model inferred from the damaged artifact. Scientists have labeled the larger surviving parts as Fragments A through G. Fragment A contains 27 gears. Fragments B through D contain one gear each. Those scientists have labeled the smaller fragments 1 through 75. Ironically, 21st-century scientists had to use cutting-edge technology to understand a device built in the Hellenistic Age.
Both recent articles based their findings on inferring the total number of “teeth” on the gear. For a base measurement, they used the remaining teeth on Fragment A, the largest gear fragment. Next, they used complex statistical techniques to estimate how many teeth would have been on the complete gear. A full discussion of their methodologies is beyond the scope of this article.
The mechanism, and its models, have the shape of a rectangular box. It has a front cover, a front plate, a back plate, and a back cover. Between the front and back plates, lie the gears. Both the front and back covers have inscriptions. Freeth described the inscriptions on the back cover as a “User Manual.” According to the “User Manual,” the front plate shows “a ‘Planetarium’: a Cosmos arranged in rings, with planets marked by “little spheres” and the Sun as a “little golden sphere” with “ray” and “pointer.” Freeth described the dial on the front plate as a Zodiac dial. This Zodiac dial would display planetary positions. The back plate has two dials that would show solar and lunar eclipses.
Its geocentric perspective
Humans subjectively experience the Sun rising in the East and setting in the West. That “motion” results from the rotation of the Earth. That perspective describes a geocentric view of the cosmos instead of a heliocentric view. In the Hellenistic Age, people had a geocentric understanding of the cosmos. This geocentric perspective worked well enough for most challenges that the ancients faced. It, however, had to account for the “backward” movements of planets. People today would call that backward motion, “retrograde.” Epicycles solved this problem. In an epicycle, a planet has a full mini orbit during its regular orbit. The ancients could predict where planets would appear to be from the perspective of the Earth. It just involved more complicated calculations. The Antikythera mechanism would have shown Mercury Retrograde.
The Horological Journal reported that the makers of the mechanism had inscribed the names of three Egyptian months on the movable calendar ring. They did so with Greek lettering. Note the calendar ring differs from the Zodiac ring. Scientists had assumed that this calendar ring represented the 365-day Egyptian Civil Calendar. That calendar had twelve 30-day months which would have made a year of 360 days.
The solar year measures about 365.24 days. This measurement marks one cycle of the Earth around the Sun. As a result of that annual extra 0.24 days, dates for solstices and equinoxes would lose alignment over time. Trying to combine lunar months and solar years produces even more problems. One solution is to insert a day or month to return to consistent dating of solstices and equinoxes. People call those inserted days or months intercalary days or months. Moderns are most familiar with February 29th as an intercalary day. With less accurate measurement systems and mathematics, the ancients used intercalary days more often than moderns do. For the Egyptian Civil Calendar, five intercalary days were added. This would produce the 365-day year of that calendar.
The Greeks lacked algebra, equations, and the concept of zero. They did, however, have a good grasp of geometry. That lack of intellectual technology makes the mechanism more impressive.
Models can help to show how the mechanism works. The mechanism itself, however, has suffered a great deal of damage. The models may reflect more from today’s current scientists than from the mechanism’s ancient fabricators. If Fragment A measures the lunar year of 354 days and not a solar year of 365.24 days, then something else in the mechanism would have to calculate the solar year correctly. The recent studies that challenged the solar year measurement did not address that question.
Archaeology, by definition, suffers from “survivor bias.” It can only study and interpret that which has been found. The Antikythera Mechanism has changed how we understand Hellenistic technology. More than texts were lost from the ancient world. New excavations of land and sea may yet reveal more unknown remnants of antiquity.
The Wild Hunt is not responsible for links to external content.
To join a conversation on this post:
Visit our The Wild Hunt subreddit! Point your favorite browser to https://www.reddit.com/r/The_Wild_Hunt_News/, then click “JOIN”. Make sure to click the bell, too, to be notified of new articles posted to our subreddit.