In the depths of history, a peculiar mystery emerges – the Antikythera mechanism. Unearthed on a small island in the Mediterranean Sea in the early 20th century, this device defied time to unveil one of ancient Greece’s most marvelous technological feats. Combining the elegance of craftsmanship with the complexities of celestial understanding, the Antikythera mechanism remains a testament to humanity’s ceaseless pursuit of knowledge and innovation.
Origins of the Antikythera mechanism
The origins of the Antikythera mechanism trace back to ancient Greece, around the 2nd century BCE. Believed to have been crafted by skilled artisans and possibly inspired by the innovative minds of mathematicians and astronomers of the time, this intricate device represents a pinnacle of ancient engineering.
Sometime before Easter 1900 captain Dimitrios Kontos and a crew of sponge divers from Symi island discovered the wreck of an ancient cargo ship off Antikythera island which is located in the north-west of Crete. Divers retrieved several bronze and marble statues and other artifacts from the site.
However, it was on May 17, 1902 that archaeologists noticed a piece of rock which was a heavily encrusted and corroded mechanism that had survived the shipwreck in three main parts and smaller fragments.
Investigations into the object lapsed until British science historian and Yale University professor Derek J. de Solla Price became interested in 1951. In 1971, Price and Greek nuclear physicist Charalampos Karakalos made X-ray and gamma-ray images of the 82 fragments. Price published a paper on their findings in 1974.
The engine of the Antikythera mechanism
The original mechanism apparently came out of the Mediterranean as a single encrusted piece. Soon afterwards it fractured into three major pieces. Other small pieces have broken off in the interim from cleaning and handling and others were found on the seafloor by the Cousteau expedition. Other fragments may still be in storage, undiscovered since their initial recovery; Fragment F was discovered in that way in 2005. Of the 82 known fragments, seven are mechanically significant and contain the majority of the mechanism and inscriptions. Another 16 smaller parts contain fractional and incomplete inscriptions.
On the front face of the mechanism, there is a fixed ring dial representing the ecliptic, the twelve zodiacal signs marked off with equal 30-degree sectors. This matched with the Babylonian custom of assigning one twelfth of the ecliptic to each zodiac sign equally, even though the consetellation boundaries were variable.
Outside that dial is another ring which is rotatable, marked off with the months and days of the Sothic Egyptian cenlandar, twelve months of 30 days plus five interrcalary. The months are marked with the Egyptian names for the months transcribed into the Greek alphabet. The first task is to rotate the Egyptian calendar ring to match the current zodiac points. The Egyptian calendar ignored leap days, so it advanced through a full zodiac sign in about 120 years.
The mechanism was operated by turning a small hand crank (now lost) which was linked via a crown gear to the largest gear, the four-spoked gear visible on the front of fragment A, gear b1.
The crank moves the date pointer about 78 days per full rotation, so hitting a particular day on the dial would be easily possible if the mechanism were in good working condition. The action of turning the hand crank would also cause all interlocked gears within the mechanism to rotate, resulting in the simultaneous calculation of the position of the Sun and Moon, the moon phase, eclipse, and calendar cycles, and perhaps the locations of planets.
Shape of the Antikythera mechanism
Front face of the Antikythera mechanism
The front dial has two concentric circular scales. The inner scale marks the Greek signs of the zodiac, with division in degrees. The outer scale, which is a moveable ring that sits flush with the surface and runs in a channel, is marked off with what appear to be days and has a series of corresponding holes beneath the ring in the channel.
Since the discovery of the mechanism, this outer ring has been presumed to represent the 365 day Egyptian calendar, but recent research challenged this presumption and provided evidence it is most likely divided into 354 intervals.
Rear face of the Antikythera mechanism
On the back of the mechanism, there are five dials: the two large displays, the Metonic and the Saros, and three smaller indicators, the so-called Olympiad Dial, which has been renamed the Games dial as it did not track Olympiad years (the four-year cycle it tracks most closely is the Halieiad), the Callippic, and the exeligmos.
The Metonic dial is the main upper dial on the rear of the mechanism. The Metonic cycle, defined in several physical units, is 235 synodic months, which is very close (to within less than 13 one-millionths) to 19 tropical years.
It is therefore a convenient interval over which to convert between lunar and solar calendars. The Metonic dial covers 235 months in five rotations of the dial, following a spiral track with a follower on the pointer that keeps track of the layer of the spiral. The pointer points to the synodic month, counted from new moon to new moon, and the cell contains the Corinthian month names.
Doors of the Antikythera mechanism
The mechanism has a wooden casing with a front and a back door, both containing inscriptions. The back door appears to be the ‘instruction manual’. On one of its fragments is written “76 years, 19 years” representing the Callippic and Metonic cycles. Also written is “223” for the Saros cycle. On another one of its fragments, it is written “on the spiral subdivisions 235” referring to the Metonic dial.
Gearing of the Antikythera mechanism
Fragment D is a small quasi-circular constriction that, according to Xenophon Moussas, has a gear inside a somewhat larger hollow gear. The inner gear moves inside the outer gear reproducing an epicyclical motion that, with a pointer, gives the position of planet Jupiter. The inner gear is numbered 45, “ME” in Greek, and the same number is written on two surfaces of this small cylindrical box.
The gear teeth were in the form of equilateral triangles with an average circular pitch of 1.6 mm, an average wheel thickness of 1.4 mm and an average air gap between gears of 1.2 mm. The teeth were probably created from a blank bronze round using hand tools; this is evident because not all of them are even.
Due to advances in imaging and X-ray technology, it is now possible to know the precise number of teeth and size of the gears within the located fragments. Thus the basic operation of the device is no longer a mystery and has been replicated accurately. The major unknown remains the question of the presence and nature of any planet indicators.
In essence, the Antikythera mechanism serves as a potent reminder of the enduring legacy of ancient Greek civilization and their contributions to human knowledge and innovation. It invites us to reconsider our perceptions of the past and recognize the profound depth of understanding that existed within ancient societies.
