An exploded view of the Antikythera mechanism. (Image Credit: Tony Freeth/UCL)
Researchers at University College London (UCL) have created a computational model of the Antikythera mechanism, a 2,000year-old ancient Greek astronomical calculator. Now, the team is constructing a replica of the mechanism, including gearwheels and all the parts, using modern machinery. If successful, they plan on reconstructing it using the same techniques from antiquity. The hand-powered mechanical device was used to predict the movements of the sun, moon, and planets along with phases of the solar and lunar eclipses.
The mechanism, known as the world’s first analog computer, was found on an ancient cargo ship off the Greek island of Antikythera in 1901, along with other artifacts. It was difficult to establish what the 82 corroded brass fragments were at first, but after decades of cleaning, scientists realized that it’s a masterful feat of mechanical engineering. The mechanism, encased in a one-foot-tall wooden box, was covered in inscriptions and contained a complex assembly of 30 gearwheels inside with dials outside. The largest piece, Fragment A, consists of bearings, pillars, and a rock. The other piece, Fragment D, contains a disk, 63-foot gear, and plate.
In 1951, Derek J. De Solla Price, a British science historian, investigated the device’s functionality. Price and physicist Charalampos Karakalos captured X-ray and gamma-ray images of the fragments. Price then theorized that the mechanism calculated the motions of stars and planets.
In 2002, Michael Wright, a former curator of mechanical engineering at the Science Museum in London, captured detailed X-ray images of the mechanism using linear tomography. His analysis showed a locked central gear in the primary wheel, which is what the other gears rotate around. His conclusion? The device mimics epicyclic motion, continuing the ancient Greek concept that planets moved in epicycles.
Wright also constructed a functioning replica by stacking the gears but never understood how the device worked. Even with the surviving 82 fragments, the task of rebuilding it was extremely difficult. Wright theorized that the mechanism may have had an upper layer, which is now missing, that housed additional gears. He also believes the lower back dial predicted eclipses. By winding the knob on the side, the celestial bodies could move forward or backward to determine their position on any given date. While turning the knob, interlocking gearwheels drove seven hands at different speeds.
It displayed celestial time. One hand represented the sun, one hand represented the moon, and five hands represented all the planets. The moon’s phase was displayed by a rotating black and silver ball. The inscriptions detailed which stars rose and set on a certain day. There were two dial systems on the back case. Each had a pin that followed its spiral groove. One was a calendar, and the other displayed the timing of lunar and solar eclipses.
Exploded view of the gear, which moves the celestial bodies in the mechanism. (Image Credit: Tony Freeth/UCL)
The UCL team’s project builds on work from Wright and the Antikythera Mechanism Research Project. They used the mechanism’s inscriptions along with a mathematical method to come up with new gear arrangements. This allowed the celestial bodies to move correctly. As a result, every gearwheel in the mechanism could fit inside a space that’s only 25mm deep.
The team believes this device showed the movements of the sun, moon, Mercury, Venus, Mars, Jupiter, and Saturn on concentric rings. However, these paths were difficult to replicate with gearwheels. They also propose using a double-ended pointer called a “Dragon Hand”, which determines when an eclipse occurs.
The team also believes this project provides them with more insight into how the Antikythera mechanism displayed the celestial bodies. Whether the device’s design is correct or could have been developed using antiquity remains a mystery. The concentric rings comprising the display would need to rotate on a set of nested, hollow axels. Without a lathe shaping the metal, it’s impossible to determine how the ancient Greeks manufactured these components.
Have a story tip? Message me at: http://twitter.com/Cabe_Atwell