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The Antikythera Mechanism

“This device is just extraordinary, the only thing of its kind. The design is beautiful, the astronomy is exactly right. The way the mechanics are designed just makes your jaw drop. Whoever has done this has done it extremely carefully … in terms of historic and scarcity value, I have to regard this mechanism as being more valuable than the Mona Lisa.[1]

These words belong to Prof. Michael Edmunds, of Cardiff University, who led a 2006 study of the Mechanism of Antikythera.

But what is the Mechanism?

The Mechanism was a wooden box the size of a thick volume (about 34 x 18 x 9 cm) housing a complex gearing mechanism; today there’s very little left of the wood, while the gears have corroded in inseparable lumps of rusty bronze, after their 2000-year stay in salty water. However, X-ray photography first, then CAT scans, revealed the fragments’ interior in surprising detail and have enabled researchers to read many of the inscriptions and draw meaningful conclusions.

What is Antikythera?

Antikythera is the place where the mechanism was discovered – a small island in the south of Greece, about halfway between the Peloponnese and the island of Crete. The Mechanism (along with many other artefacts) was recovered from an ancient shipwreck discovered, in 1900, at a depth of 45m off the coast of the island.

 But why is the Mechanism so important?

First of all, because it is amazing how many things it can measure and how accurately it can do so. As a work of art it is unsurpassed in its boldness of conception and mastery of execution. But as a work of craftsmanship it goes beyond that: in order for all its functions to fit in such a small box, one needed not only advanced engineering but mindbogglingly precise execution too.

Secondly, it proved beyond doubt that all the descriptions of such devices in ancient manuscripts refer to real objects (which had actually been constructed and put to use) and not theoretical constructs which were never actually made. Experts thought it was impossible for such complex gearing to have existed  a full 14 centuries before the first clocks appeared. Yet it is now obvious that not only Greeks knew how to make gears, but they combined them in complex and ingenious ways that had to be re-invented centuries later. The complexity of the mechanism has amazed even Swiss watchmakers.

Antikythera-gearing-schematic

Thirdly, it reveals a depth of astronomical knowledge that is difficult to imagine today. At an age when few of us even notice the phase of the moon, ancient people had observed even the tiniest variations in its motion and the motion of other celestial bodies and had figured out they occurred periodically; they had even calculated how often that happened. They did not yet know how to interpret these anomalies, but that doesn’t diminish their accomplishment, in an age without telescopes.

What does it do?

The Mechanism is not a clock; it was not made to measure the hours of the day. Instead, it measures years and astronomical cycles that last for decades; it predicts eclipses; it reproduces the motion of the sun, the moon and the planets[2]. In short, the Mechanism is an astronomical calculator-cum-orrery, made to display and predict celestial phenomena and, perhaps, make or adjust calendars. At a time when every region had its own system of measuring time, this was probably essential.

But let’s take things one at a time:

The front:

  1. It shows the Egyptian Calendar, by means of a dial marked with the Egyptian months (transliterated into Greek; with a length of 365 days, the Egyptian calendar was reformed in 238 BCE by the Greek Ptolemaic dynasty, to include a leap year every 4 years, making it the most accurate of its time. The Mechanism’s dial does not include leap days but its maker and user were aware of them: the inner dial is made to move against the outer, to compensate for a day every 4 years).
  2. It shows the Solar year, by means of a second dial, within the first, marked with the signs of the Zodiac. (Conforming to the Babylonian tradition, the zodiac is divided in 12 equal segments, even though the constellations themselves are not of equal size.)
  3. It showed the position of the sun in the ecliptic (i.e. against the stars), by means of a pointer moving across the face of both dials (i.e. for any given date, what the position of the sun in the sky is).
  4. It showed the position of the moon against the stars, by means of a second pointer. The Mechanism used a very sophisticated epicyclic gearing system to show the irregularities of the moon’s movement across the sky, including its precession across the ecliptic, caused by its elliptical orbit. (more about that below)
  5. It showed the phases of the moon, by means of a spherical model of the moon, attached to the moon’s pointer; it was half black and half white and turned to display the phase.
  6. It showed the position of important stars and constellations in the ecliptic, as well as their rising or setting time, by means of symbols in the inner dial (which corresponded to a legend outside the dials).
  7. It shows the positions of Mercury, Venus, Mars, Jupiter and Saturn (the 5 planets known in antiquity). Their existence was speculated for a long time, as the names of Mars and Venus had been read in the surviving inscriptions; the 2005 research confirmed their existence, meaning that including the sun and moon, the Mechanism tracked the motion of 7 bodies of our solar system.[3]
  8. Speculated: Since the maker of the mechanism went into the trouble of showing the elliptical anomaly of the moon’s position, it is quite possible that the sun’s anomalous motion was shown by similar means. However, the gearing for this has not been discovered yet. 

The back

With no less than 5 separate dials, the back is far more complicated than then front.

  1. It showed the Metonic cycle, in the large upper dial. The Metonic cycle is essentially an observation that the sun and moon cycles coincide almost perfectly every 235 lunar months or 19 solar years. This was used to improve calendar accuracy by calculating how many leap days should be inserted and how often. It is interesting that the names of the months in the dial correspond to those in the Corinthian calendar.
  2. It showed the Callipic cycle of 79 years, which refined the Metonic system, removing one day after 4 Metonic cycles, in order to better synchronise the lunar calendar with the year. The Callipic dial is a small circle within the Metonic one, on the left. Its pointer moves across its 4 sections, indicating which of the 4 Metonic cycles (contained within the Callipic cycle) we’re currently in.
  3. It showed which Greek games took place each year: the Olympic Games of Olympia, the Pythian Games of Delphi and the Naia Games of Dodona (taking place every 4 years but not on the same year); the Isthmian Games of Corinth and the Nemean Games of Nemea (every 2 years) and another event, ending in –EIA (possibly Alieia, in honor of the sun, held in Rhodes)[4]. This small dial was also within the Metonic one, on the right.
  4. It predicted eclipses, by means of a second large dial, below the Metonic one, showing the Saros cycle. A Saros cycle is a period of about 223 lunar months, after which the Earth, Sun, and Moon return to approximately the same relative positions. That means that Solar and Lunar eclipses occur at approximately the same time and in the same manner in every cycle; the cycle is therefore a tool for determining when eclipses will take place.
  5. It predicted the time of day an eclipse would occur, by means of the Exeligmos dial, contained within the larger, Saros dial. As the Saros cycle has a length of 18 years, 11 days and 8 hours (i.e. a third of a day), eclipses happen at different times of the day or night for 3 cycles, then repeat. The Exeligmos dial is essentially a 54-year long period that corresponds to 3 Saros cycles. For the 1st cycle the dial indicates the addition of 0 hours, for the second, 8 hours and for the 3rd, 16 hours, permitting more accuracy in predicting what time the eclipse will occur.

 How does it work?

Obviously, the Mechanism was not powered by electricity, nor does it contain software. The user would move the Sun pointer to the desired date and all things would fall into place; then he or she could move backwards or forwards in time by turning a knob on the side (which is now missing, but we know it was there, connected to the other gears in the mechanism by means of a crown gear).

If you wish to see how it all fitted and worked together, you may want to watch this amazing video, or visit this page for a more analytical look.

How did it perform its computations?

By combining the ratios of gears with different sizes and number of “teeth” the Mechanism was able to “calculate” the relationship among different celestial events over time. In this it was not unlike the first mechanical calculators invented in the 18th century, such as Pascal’s calculator or the analog firing computers.

For a mathematically challenged person like me, how these calculations were performed is difficult to grasp; the simplest explanation (and illustration) I could find of how this was done is in a video of a 2010 reconstruction of the Mechanism, made using Legos. Another option is this video, explaining in layman’s terms the principles behind analog firing computers.

Mindboggling knowledge and craftsmanship

But how did the Mechanism imitate the motion of celestial bodies in the sky? Planetary movements are not as simple as we may imagine. Take the moon for example: it follows an elliptical orbit, which makes it move at a different speed on different days. I didn’t know about that, but ancient astronomers did. But, although they were familiar with the phenomenon, they had no idea why it happened, until the 2nd century BCE, when Hipparchus, an astronomer who lived in Rhodes, proposed a theory that seemed to explain the observations. The Mechanism seems to incorporate this knowledge and shows the moon’s orbit as it actually is (sometimes faster, others slower).

But how does it do that? Here’s where things get interesting.

Antikythera-moon-gears

The gear train that drives the moon’s pointer consists of 4 gears. One of them is not fixed to the same axle as the others but rather uses a pin to turn the last gear by pushing on the edge of a small radial slot in it. The two gears are mounted slightly off-axis from each other so that, as they turn, the pin is sometimes nearer and other times further away from the last gear, causing a varying rate of rotation to the lunar pointer, which agrees with observations from Earth. But that’s not all: the variable speed gears are mounted on another, larger gear, which makes the variation occur at the correct observed period, which is slightly different from the period of the moon’s orbit around the Earth. This mounting of gears on other gears is known as “epicyclic gearing.” You may get an idea of how this worked by watching this video

The question is how advanced was the math which allowed the crafting of gears with such precision? How many years of experimentation did it take to get the design exactly right? How many centuries had gears been used before the Greeks ended up with artisans who could produce mechanisms of such incredible sophistication?

Who was it made for and why?

It is beyond doubt that the Mechanism was designed by someone with thorough knowledge of astronomy, an heir to the Babylonian tradition, whose astronomical records went back for centuries, allowing general conclusions to be gleaned from this treasure trove of data. This tradition must have been carried over to the Greek world; Thales of Miletus, the first man known to have predicted an eclipse (the solar eclipse of 585 BCE, which occurred during a battle between Persia and Lydia), must have had access to such data.

However, the extensive instructions[5] on the Mechanism prove that it was destined to be used by a person (or persons) who knew substantially less; actually, if it weren’t for these instructions, it is quite possible that archaeologists would still be puzzling over its function.

P1490631

The additional fact that the Mechanism calculates –along with the “grand” astronomical phenomena– something as simple as the time of athletic events, is another indication that it had not been designed for the exclusive use of astronomers but for a wider audience. 

It is not unlikely that it had been ordered by one of the Greek monarchs of Hellenistic times – whether for astronomical use or simply for “show” remains unknown. It could also be a teaching tool, employed by a learning institute, such as a philosophical school or library.

Unfortunately, the lack of any further information means that all such theories are destined to remain mere conjecture.

How did it end up on a ship bound for Rome?

Personally, I agree with the theory that the Mechanism was on the ship as part of a shipment of luxury Greek items bound for Rome (or another Roman port). Once there, if it were part of public war booty, it would end up in a public space; if not, it would end up as a personal acquisition (like the Mechanism of Archimedes) of a Roman patrician, who would either know how to use it or would simply use it to dazzle his guests with.

(I can almost imagine the item paraded in a rich Roman house after dinner and the host trying to impress his guests by daring them to wager when the next eclipse would take place.)

Anton-von-Werner-The-Symposion-1877

When was it made?

Judging by the style of the letters used in the mechanism, archaeologists date its making sometime between 150-100 BBE, a generation or more before the shipwreck[6].

Another theory, based on the analysis of how the Mechanism predicted eclipses, date its construction even earlier, perhaps in 205 BCE, when its Saros cycle is at its most accurate.

Where was it made?

Perhaps we will never know exactly where the Mechanism was made. Any Greek city might have been its birthplace and the ship which carried it certainly had visited quite a few, judging by its contents. However, a flourishing city somewhere in the Eastern Aegean or Eastern Mediterranean seems likely, especially one with an astronomical tradition or an institute of learning.

If the Mechanism used only the Egyptian calendar, then it would be very probable that it was made in Alexandria, Egypt. However, in the Metonic dial, the Corinthian calendar is used, which makes it more likely that the Mechanism was made for use in a place which followed this system; of these Syracuse and Rhodes are perhaps the best candidates, as both were academic centres that had produced excellent scientists. Syracuse was the home city of Archimedes, a scientist on a par with Galileo and Newton, who is credited with inventing and creating one such mechanism. On the other hand, Rhodes had Hipparchus, the astronomer who proposed a theory that seemed to explain the anomalies of the moon’s motion across the sky.

But, as I’ve said before, lack of any written source makes it unlikely that we’ll ever know for certain.

How was it made?

Ancient Greeks are still admired for their craftsmanship; metal working was no exception. As inheritors of a centuries-long tradition, they had experience which allowed them to do things we cannot replicate today, even with modern tools (ask the Acropolis restorers). The Mechanism was made using simple steel tools by skilled artisans who also knew enough of math and geometry to achieve near perfection in crafting the gears.

Michael Wright, who studied the Mechanism for decades, made a working model using ancient tools and techniques, proving that it was indeed feasible for the mechanism to be made without modern means.

How was its significance revealed?

When the mechanism was first discovered, someone almost threw the pieces overboard as useless rocks, but was stopped by another, who noticed traces of metal. At the National Archaeological Museum, the mechanism was left in a box for conservators to determine whether any of the pieces belonged to the bronze statues undergoing conservation[7].

On May 17th, 1902, former Minister of Education, Spyridon Stais, and Curator of Antiquities, Gabriel Byzantinos, were the first to notice that one of the curious objects had gears, inscriptions and traces of wood. That was the point when the effort to identify what it is began.

Several people studied it: I. Svoronos and A. Willhelm (1902); G. Athanasiadis and O. Rousopoulos (1902); P. Rediadis (1903); K. Rados (1905); V. Stais (1905); A. Rehm (1907); H. Diels (1924); I. Theofanidis (1925-1930); R. Gunther (1932); G. Karo (1948); W. Hartner (1967). They used photography (simple or under raking light) to read several inscriptions; they brought their own skills and expertise to solve the seemingly intractable problem; they disagreed about what it could be (from astrolabe, to navigational instrument to planetarium) and when it was made (1st century BCE – 5th century CE). But all of them came closer to solving the mystery, one question at a time[8].

In 1951, an English Historian of Science, Derek De Solla Price, devoted 8 years to studying it, using X-ray photography and the help of epigraphist G. Stamiris. He identified it as a lunar-solar calendar calculator following the tradition of Archimedes’s planetary devices. His famous monograph in 1959 proved the basis of all future research. He followed it up with a book publication, in 1974, with more radiographs by C. Karakalos; he also constructed a reconstruction of the Mechanism.

Wright, with the help of A. Bromley, re-examined the mechanism’s fragments using linear CAT scans. They altered Price’s reconstruction based on the epicyclical model of Hipparchus’s theory of the universe (1986). Wright finally concluded that the Mechanism was a planetarium, which could predict the movement not only of the sun and moon but of all the other known planets too (2003). He constructed his own model in 2005[9].

More researchers followed: J. Evans, C. Carman and A. Thorndike (2010); T. Freeth and A. Jones (2012); and M. Edmunds, who stressed the need to study the artifact using non-destructive 3D imaging technology and was instrumental in establishing the Antikythera Mechanism Research Project[10]

Using cutting-edge technology

In 2005 the Antikythera Mechanism Research Project was undertaken by the Greek ministry of Culture and was carried out by an international team. They used digital photography; chemical analysis (using broad spectrum element-specific x-ray imaging); Polynominal Texture Maps (PTMs) by Hewlett Packard; and “Bladerunner” (Turbine Blade Computed Tomography and Measurement System) by X-Tek. The results (2006) revealed unprecedented details: they confirm the presence of 30 gears and enabled the reading of twice as many letters as had been read in the previous century. The team constructed a new digital model and dated the device to 150-100 BC on palaeographic grounds (i.e. the style of the lettering)[11].

 

The Mechanism today

Despite the fact that only about 1/3 of the Mechanism survives, it is recognized as one of the most important archaeological finds ever. Technology may have answered many of our questions about it, but there are still a lot of things we don’t know about it and perhaps never will. A recent exploration of the Antikythera shipwreck has yielded yet more finds. As these are analyzed and as technology advances, we may expect more of the Mechanism’s secrets revealed.


[1] Scientists Unravel Mystery of Ancient Greek Machine; Live Science. Retrieved April 2016.

[2] The Antikythera Shipwreck, 2012, p. 239.

[3] Ibid.

[4] Ibid., p.247.

[5] Thirty-seven lines, 1380 letters (of which 560 complete words) preserved; ibid., p. 245.

[6] Ibid., p.240.

[7] Ibid., p. 228.

[8] Ibid., pp. 228-30.

[9] Ibid., p. 230.

[10] The Antikythera Mechanism; seeing inside a two-thousand-year old computer

[11] Ibid., p. 240.


Image sources

Front dial: http://dlib.nyu.edu/awdl/isaw/isaw-papers/4/images/figure04.jpg

Back dials: https://upload.wikimedia.org/wikipedia/en/4/4b/Computer_graphic_for_back_of_Antikythera_mechanism.jpg

Moon’s gearing: http://www.kpbs.org/news/2013/mar/29/nova-ancient-computer/

Roman dinner party (symposium): http://antinousgaygod.blogspot.gr/2015/11/how-to-plan-your-own-festive-antinous.html

All the other images are from the catalog of the 2012 exhibition (see below).


Further reading:

All of the links above contain useful information about the Mechanism of Antikythera. My main source of information has been the catalog of the Antikythera Exhibition at the National Archaeological Museum in Athens:

The Antikythera Shipwreck. The Ship, The Treasures, The Mechanism. National Archaeological Museum, April 2012 – April 2013“. Hellenic Ministry of Culture and Tourism; National Archaeological Museum. Editors Nikolaos Kaltsas & Elena Vlachogianni & Polyxeni Bouyia. Athens: Kapon, 2012, ISBN 978-960-386-031-0.

The site of The Antikythera Mechanism Research Project is a good place to go to for questions and answers about the Mechanism; it is also a treasure trove of information about the Mechanism.

This video  contains a lot of information about the Mechanism, including its history, efforts to understand it and what it could do and how.

You may also want to take a look at the following:

Carman, C., Thorndike, A., Evans, J., On the pin-and-slot device of the Antikythera Mechanism, with a new application to the superior planets

Evans, J., Carman, C., Thorndike, A., Solar anomaly and planetary displays in the Antikythera Mechanism

Freeth, T., Jones, A., Cosmos in the Antikythera Mechanism

Freeth, T., Decoding an Ancient Computer

Freeth et al., Decoding the Antikythera Mechanism: Investigation of an Ancient Astronomical Calculator

Gallagher, S., Gears of War; when mechanical analog computers ruled the waves

Haughton, B., Hidden History: Lost Civilizations, Secret Knowledge, and Ancient Mysteries

Price, Derek de Solla, Gears from the Greeks. The Antikythera Mechanism: A Calendar Computer from ca. 80 BC.

Wright, M.T., The Antikythera Mechanism and the Early History of the Moon-Phase Display

 

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