The mechanism and a modern day recreation

In 1902, archaeologist Valerios Stais discovered the Antikythera mechanism, an ancient analog computer from the first or second century B.C., that was used to calculate the position of the sun, moon, and stars in relationship to the observer’s position on the surface of the earth. Stais uncovered the mechanism while exploring the Anitkythera shipwreck off the northwest coast of Crete. Divers discovered the sunken ship in 1900 and had already unearthed statues, musical instruments, and other artifacts. Stais guessed that the mechanism was a clock and other archaeologists conjectured it was some type of astronomical device.

For many decades, archaeologists did not recognize the mechanism’s degree of mechanical sophistication, which is comparable to a 19th-century Swiss clock. To date, the only other artifacts with that degree of mechanical sophistication have come from the 14th century or later.

My own interest in the mechanism is simply that it changes our understanding of the history of technology and astronomy. I marvel at what the ancients were thinking about and trying to create to understand the world. The miniaturization and the complexity of its parts is compared to that of 19th century clocks. It has over 30 gears, although Michael Wright (see below) has suggested as many as 72 gears, with teeth formed through equilateral triangles.

It was made to position astronomical bodies with respect to the celestial sphere, with reference to the observer’s position on the surface of the Earth. Therefore, the device was based on the geocentric model.

In astronomy, the geocentric model (also known as geocentrism, or the Ptolemaic system), is the superseded theory, that the Earth is the center of the universe, and that all other objects orbit around it. This geocentric model served as the predominant cosmological system in many ancient civilizations such as ancient Greece. As such, most Ancient Greek philosophers such as Aristotle and Ptolemy assumed that the Sun, Moon, stars, and naked eye planets circled the Earth.

The mechanism has between 30 and 70 very small gears and underwent years of cleaning. British science historian Derek J. de Solla Price began to investigate it and realized its significance.

The front dial that showed the progress of the sun and moon through the zodiac. An upper rear dial showing various monthlong and yearlong cycles and a lower rear dial that tracked the progress of a single month with an adjoining dial that tracked the 12 months of the lunar year.

The mechanism is the oldest known complex scientific calculator.

With its many gears, it is sometimes called the first known analog computer. The manufacturing is so well done that it is logical to assume that it may have had a number of predecessors from the Hellenistic Period that have yet to be discovered or are lost to time.

It appears to be constructed upon theories of astronomy and mathematics developed by Greek astronomers. It is estimated that it was made around 150-100 BC in the Greek-speaking world. (All the instructions of the mechanism are written in Koine Greek.

One hypothesis is that the device was constructed at an academy founded by the Stoic philosopher Posidonius on the Greek island of Rhodes, which at the time was known as a center of astronomy and mechanical engineering, and that perhaps the astronomer Hipparchus was the engineer who designed it since it contains a lunar mechanism which uses Hipparchus’s theory for the motion of the Moon.

Recent findings published in the July 31, 2008, edition of Nature, alternatively suggest that the concept for the mechanism originated in the colonies of Corinth, which might imply a connection with Archimedes.

There is a good video on the journal Nature’s website that gives an overview of the work being done and shows animations of the mechanism in operation.  The Wikipedia entry has a good article and many links to the research being done.

The mechanism has three main dials, one on the front, and two on the back. The front dial has two concentric scales. The outer ring is marked off with the days of the 365-day Egyptian calendar, or the Sothic year, based on the Sothic cycle. Inside this, there is a second dial marked with the Greek signs of the Zodiac and divided into degrees. The calendar dial can be moved to compensate for the effect of the extra quarter day in the solar year (there are 365.2422 days per year) by turning the scale backwards one day every four years. Note that the Julian calendar, the first calendar of the region to contain leap years, was not introduced until about 46 BC, up to a century after the device was said to have been built.

The front dial probably carried at least three hands, one showing the date, and two others showing the positions of the Sun and the Moon. The Moon indicator is adjusted to show the first anomaly of the Moon’s orbit. It is reasonable to suppose the Sun indicator had a similar adjustment, but any gearing for this mechanism (if it existed) has been lost. The front dial also includes a second mechanism with a spherical model of the Moon that displays the lunar phase.


A modern day recreation of how the Olympiad dial would have appeared

Today the mechanism is on display at the National Archaeological Museum of Athens and is studied by the Antikythera Mechanism Research Project. A number of museums have built recreations based on the research.  In 2008, the Project found the inscription “Olympia” on the mechanism, and they now think the device may have been used, in part, to track the occurrence of the ancient Olympic games.

The new discoveries confirm that the mechanism is an astronomical analog calculator or orrery used to predict the positions of celestial bodies. This work proposes that the mechanism possessed 37 gears, of which 30 survive, and was used for prediction of the position of the Sun and the Moon, planetary motions and events like eclipses.

The ancients lay on the ground in the same way that we did to marvel at the night sky and wonder.

When I heard the learn’d astronomer;
When the proofs, the figures, were ranged in columns before me;
When I was shown the charts and the diagrams, to add, divide, and measure them;
When I, sitting, heard the astronomer, where he lectured with much applause in the lecture-room,
How soon, unaccountable, I became tired and sick; 5
Till rising and gliding out, I wander’d off by myself,
In the mystical moist night-air, and from time to time,
Look’d up in perfect silence at the stars.

Walt Whitman, Leaves of Grass