Friday, October 13, 2017


For over 2000 years a shipwreck lay off the coast of the Greek island of Antikythera, its hidden treasures slowly corroded by the Mediterranean. It wasn’t until 1900 that sponge divers happened upon the loot, and found therein a perplexing device of remarkable engineering - though the divers had no idea how truly remarkable it was at the time. The device sat in a museum for fifty years before historians began to take a serious look at it.

The mechanism was built circa 200 BC, and, with over thirty gears hidden behind its dials, it is easily the most advanced technological artifact of the pre-Christian period. Regarded as the first known analog computer, the mechanism can make precise calculations based on astronomical and mathematical principles developed by the ancient Greeks. Although its builder’s identity and what it was doing aboard a ship remain mysteries, scientists have worked for a century to piece together the mechanism’s history.Known as the Antikythera mechanism and called a “clockwork computer,” this small bronze instrument is unique because it precedes any machine of comparable complexity by more than a millennium.  
Somewhat surprisingly, most consider it unlikely that the Antikythera mechanism was a navigational tool. The harsh environment at sea would have presented a danger to the instrument’s delicate gears, and features such as eclipse predictions are unnecessary for navigation. The mechanism’s small size, however, does suggest that it was designed with portability in mind. According to some researchers, a more plausible story is that the mechanism was used to teach astronomy to those with little knowledge of the subject.
To use the instrument, you would simply enter a date using a crank, and, when the gears stopped spinning, a wealth of information appear at your fingertips: the positions of the Sun, Moon, planets, and stars, the lunar phase, the dates of upcoming solar eclipses, the speed of the Moon through the sky, and even the dates of the Olympic games. Perhaps most impressively, the mechanism’s calendar dial could compensate for the extra quarter-day in the astronomical year by turning the scale back one day every four years. The Julian calendar, which was the first in the region to include leap years, was not introduced until decades after the instrument was built.
While the Antikythera mechanism is the only known artifact of its kind, its precise engineering and the fact that similar instruments were described in contemporary writing lend strong support to the notion that it was not unique. It is thought that the famous inventor Archimedes of Syracuse constructed comparable devices. Some believe that the instrument came from the school of the astronomer Hipparchus. Whoever the builder was, they were likely Greek, as evidenced by the written instructions that are attached to the instrument’s face.
Today, the Antikythera mechanism is housed is in the Bronze Collection of the National Archaeological Museum of Athens. A replica of the mechanism is also on view at the American Computer Museum in Bozeman, Montana. When Jacques-Yves Cousteau made his last visit to the shipwreck in 1978, he found no additional pieces. Nevertheless, the device continues to reveal its secrets to the researchers of the Antikythera Mechanism Research Project, an international effort supported by various universities and technology companies. ... [1] 

How operates Mechanism

Schematic of the artefact's known mechanism
Information on the specific data gleaned from the ruins by the latest inquiries is detailed in the supplement to Freeth's 2006 Nature article.
On the front face of the mechanism (see reproduction here:) 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 constellation boundaries were variable. Outside of that dial is another ring which is rotatable, marked off with the months and days of the Sothic Egyptian calendar, twelve months of 30 days plus five intercalary days. The months are marked with the Egyptian names for the months transcribed into the Greek alphabet. The first task, then, 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.    ...[2] 
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, the gear named b1. This moved the date pointer on the front dial, which would be set to the correct Egyptian calendar day. The year is not selectable, so it is necessary to know the year currently set, or by looking up the cycles indicated by the various calendar cycle indicators on the back in the Babylonian ephemeris tables for the day of the year currently set, since most of the calendar cycles are not synchronous with the year. 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.

The operator also had to be aware of the position of the spiral dial pointers on the two large dials on the back. The pointer had a "follower" that tracked the spiral incisions in the metal as the dials incorporated four and five full rotations of the pointers. When a pointer reached the terminal month location at either end of the spiral, the pointer's follower had to be manually moved to the other end of the spiral before proceeding further...[3] 


1 . Nation museum of Greece. 
2 . Freeth's 2006 Nature article.
3.  Decoding the Antikythera Mechanism, the First Computer. 

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