A team of researchers from University College London and the Cyprus Institute’s Science and Technology in Archaeology and Culture Research Center has solved a major piece of the puzzle that makes up an ancient Greek astronomical calculator called the Antikythera Mechanism.

Computer model of the Antikythera Mechanism’s display: in the center, the dome of the Earth, the phase of the Moon and its position in the Zodiac — then rings for Mercury, Venus, true Sun, Mars, Jupiter, Saturn and Date, with ‘little sphere’ markers and smaller markers for oppositions. Scale marks and index letters for the synodic cycles of the planets are inscribed on the planet rings. Surrounding these, the Zodiac and the Egyptian Calendar. The true Sun ring has a ‘little golden sphere’ with ‘pointer.’ When the Moon and Sun pointers coincide, the Moon sphere shows black for New Moon; when the pointers are on opposite sides, the Moon sphere shows white for Full Moon. The Head of the Dragon Hand shows the ascending lunar node; the Tail the descending node. Small triangles on the true Sun ring, near the pointer, show wider and narrower eclipse limits. Eclipses are possible if the Dragon Hand is within these limits. When the Moon pointer is before the Head of the Dragon, the Moon is South of the node; after, it is North of the node — conversely for the descending node. A Date pointer is attached to a narrow date ring, showing the date in the Egyptian Calendar. Image credit: Freeth et al., doi: 10.1038/s41598-021-84310-w.

In 1900, a team of Greek sponge divers discovered a 2,050-year-old Roman shipwreck off the remote island of Antikythera in Greece.

The 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 divers recovered a rich collection of ancient artifacts from the wreck site, including bronze and marble statues, jewelry, furniture, luxury glassware, and a surprisingly complex device now known as Antikythera Mechanism.

Constructed between 150 and 100 BCE, it was a mechanical computer of bronze gears that used ground-breaking technology to make astronomical predictions, by mechanizing astronomical cycles and theories.

“It calculated the ecliptic longitudes of the Moon, Sun and planets; the phase of the Moon; the Age of the Moon; the synodic phases of the planets; the excluded days of the Metonic Calendar; eclipses — possibilities, times, characteristics, years and seasons; the heliacal risings and settings of prominent stars and constellations; and the Olympiad cycle — an ancient Greek astronomical compendium of staggering ambition,” said University College London’s Professor Tony Freeth and colleagues.

Now split into 82 fragments, only a third of the original survives, including 30 corroded bronze gearwheels.

Nevertheless, they are rich in evidence at the millimeter level — with fine details of mechanical components and thousands of tiny text characters, buried inside the fragments and unread for more than 2,000 years.

The biggest surviving fragment, Fragment A, displays features of bearings, pillars and a block. Another, Fragment D, features an unexplained disk, 63-tooth gear and plate.

In previous research, scientists revealed thousands of text characters hidden inside the fragments using microfocus X-ray computed tomography.

Inscriptions on the back cover include a description of the cosmos display, with the planets moving on rings and indicated by marker beads.

It was this display that Professor Freeth and co-authors worked to reconstruct.

Inscriptions on the Antikythera Mechanism. (a) FRONT COVER: Planet cycles, framed by molding from Fragment 3. FRONT PLATE: Parapegma, above and below the Cosmos Display, indexed to the Zodiac Dial. BACK PLATE: Month names on the Metonic Calendar. Eclipse characteristics, round Metonic Calendar and Saros Eclipse Prediction Dials — indexed to the latter. Eclipse glyphs indexed to the Saros Dial. BACK COVER: User Manual, including Cosmos description, Calendar Structure and Moon-Sun Cycles. (b) Front Cover Inscription (FCI): composite X-ray CT from Fragments G, 26 and 29 and other small fragments. The FCI describes synodic cycles of the planets and is divided into regions for each planet in the customary cosmological order (CCO). The numbers ΨΞΒ (462) in the Venus section and ΨMΒ (442) in the Saturn section are highlighted. (c) Back Cover Inscription (BCI): composite X-ray CT from Fragments A and B. A User Manual: the upper part is a description of the front Cosmos Display with planets in the CCO; in red are the planet names as well as the word KOΣMOY – ‘of the Cosmos.’ Image credit: Freeth et al., doi: 10.1038/s41598-021-84310-w.

“Ours is the first model that conforms to all the physical evidence and matches the descriptions in the scientific inscriptions engraved on the Mechanism itself,” Professor Freeth said.

“The Sun, Moon and planets are displayed in an impressive tour de force of ancient Greek brilliance.”

Two critical numbers in the X-rays of the Mechanism’s front cover, of 462 years and 442 years, accurately represent cycles of Venus and Saturn respectively.

When observed from Earth, the planets’ cycles sometimes reverse their motions against the stars.

Astronomers must track these variable cycles over long time-periods in order to predict their positions.

“The classic astronomy of the first millennium BCE originated in Babylon, but nothing in this astronomy suggested how the ancient Greeks found the highly accurate 462-year cycle for Venus and 442-year cycle for Saturn,” said Aris Dacanalis, a Ph.D. candidate in the Department of Mechanical Engineering at University College London.

Using an ancient Greek mathematical method described by the philosopher Parmenides, the team not only explained how the cycles for Venus and Saturn were derived but also managed to recover the cycles of all the other planets, where the evidence was missing.

“After considerable struggle, we managed to match the evidence in Fragments A and D to a mechanism for Venus, which exactly models its 462-year planetary period relation, with the 63-tooth gear playing a crucial role,” said David Higgon, a Ph.D. candidate in the Department of Mechanical Engineering at University College London.

“We then created innovative mechanisms for all of the planets that would calculate the new advanced astronomical cycles and minimize the number of gears in the whole system, so that they would fit into the tight spaces available,” Professor Freeth said.

“This is a key theoretical advance on how the Cosmos was constructed in the Mechanism,” said Dr. Adam Wojcik, also from the Department of Mechanical Engineering at University College London.

“Now we must prove its feasibility by making it with ancient techniques. A particular challenge will be the system of nested tubes that carried the astronomical outputs.”

The team’s results were published in the journal Scientific Reports.


T. Freeth et al. 2021. A Model of the Cosmos in the ancient Greek Antikythera Mechanism. Sci Rep 11, 5821; doi: 10.1038/s41598-021-84310-w