Antikythera Mechanism - An Overview on the Ancient Analogue Computer

 

   People always find solving an ancient mystery interesting. But what we are going to discuss here is something that has amazed some of the greatest minds of the planet, the Antikythera Mechanism. Why is the Antikythera Mechanism important? What does it do? Why is it so special? Let us dive in and get our answers.

Front side of the largest fragment of Antikythera Mechanism
Credits: Wikipedia Commons

   Nowadays, gear systems have reached tremendous advancements and applications. Some of these systems are hard to understand and follow through. Imagine having these systems 2000 years before. This Antikythera Mechanism has not one, but 30 gears. This kind of complex mechanism developed in ancient world is what makes it special.

   The mechanism along with various other artefacts were discovered in a shipwreck near the Antikythera Island of Greece in 1901 and hence the name. It was found within a wooden box of dimensions 34 cm x 18 cm x 9 cm. It then disintegrated into 3 fragments. At the beginning it was considered as a bronze lump and left aside as the other artefacts were considered important.

Location of Antikythera Wreck in the Kythira Strait

   Year later, in 1902, Valerios Stais, an archaeologist spotted a gear like mechanism embedded in one of the fragments. At that time it was considered as a form of an astronomical clock. Some of the scholars believed the mechanism to be way ahead of its time. Later studies on the mechanism were dropped.

   Interests in the mechanism resurfaced around 1950s. At this point it had been broken down to 82 fragments. The complete X-Ray and gamma ray studies of the mechanism were conducted. Later few expeditions to search for other parts were conducted but none of such parts had been recovered.

   There are various theories about the origin of the mechanism. According to Roman philosopher Cicero, similar devices have been created by Greek polymath Posidonius in the 1^st century BC, who also constructed a planetary model. Since the mechanism is known to be astronomical orrery, this theory looks promising.

   The mechanism is actually based on the astronomical and mathematical theories put forward by the Greek astronomers in the 2^nd century BC. Other artefacts found in the wreck are of Rhodian origin. The location of the wreck is in between the Kythira Strait which is commonly used by traders to move between Italian ports and Rhodes.

   Moreover, astronomer Hipparchus belonged to Rhodes. He was active between 140-120 BC. He was the person who explained the irregular motion or irregular orbit of the moon around the Earth. This was used in the Antikythera Mechanism as well.

   The mechanism was found to work better between the latitudes of 33.3 – 37.0˚N. The island was found to be located between the latitudes of 35.85 – 36.50˚N. So, there was a real chance that this mechanism could have been developed by Hipparchus or maybe on the Island of Rhodes.

   The mechanism has been heavily damaged by the sea floor. Out of 82 fragments, only 7 are significant which contain majority of the mechanism. Most of the minor fragments contain no piece of values. But 16 minor fragments are known to harbor fractional inscriptions in Koine Greek dialect.

   Now let us discuss about the dials and operations. The mechanism contains dials on both the front and back sides with a crank handle connected to the largest gear in the mechanism through the crown gear. It is enclosed in a wooden box with both front and back doors.

Front side of a replica found in National Archaeological Museum in Athens
Credit: Giovanni Dall'Orto via Wikipedia Commons

   The front face has a circular dial representing the plane of Earth’s orbit around the Sun. The dial contains the 12 zodiac signs equally partitioned into 30˚ sectors. Outside the dial is a rotatable ring which describes the month and days of the ancient Egyptian Calendar. The mechanism has few inscriptions of Egyptian month names in Greek language.

   This Egyptian Calendar contains 365 days as the modern calendar. But the months are of 30 days only which accounts for only 360 days. The remaining five days are considered as an intercalary month. The mechanism does not include these five days along with the concept of leap years.

   The ecliptic plane has two pointers, the Lunar and Sun pointers. The crank head rotation will make the interlocked gear system to rotate providing the simultaneous calculation of Sun, Moon, phases of Moon and even eclipses. There is a possibility for the presence of planet pointers for the five known planets at that time.

Back side of the same replica as the front side on display
in National Archaeological Museum, Athens
Credit: Giovanni Dall'Orto via Wikipedia Commons

   The back face contains five dials. Two dials are larger and displays Metonic and Saros Calendars. The Metonic Calendar dial is the upper primary dial which covers 235 months roughly 19 years. The dial covers these 235 months through five rotations.

   The Callippic dial is the left secondary upper dial which shows the Callipic cycles. Each Callippic cycle contains 76 years, four Metonic cycles. This dial denotes the current Metonic cycle in the overall Callippic cycle.

   On the upper right side is the games dial. The dial is equally divided into four parts. These sectors denote various Greek games. The Games of Olympia and Isthmia are mentioned in the inscription. This provides information about the usage of the mechanism for calculating the dates of such games.

   The lower primary dial is the Saros dial. One Saros cycle is equal to 18 years and 11 1/3 days. This is close to 223 months. The Exeligmos dial which is the secondary lower dial covers 54 years. One Exeligmos cycle covers three Saros cycle rounding the 1/3 days to a complete day.

   The wooden box inside which the mechanism is placed contains two doors, both back and front. The back door contains the instruction manual. There are several inscriptions translating to “76 years” (Callippic Cycle), “19 years” (Metonic Cycle) and “223” ( Saros Cycle), providing proof for the back dials of the mechanism.

   The gearing is one of the complex ones here. Functions of only 9 of the gears and pointers have been identified. The reconstructions created by Freeth and Jones add six more to the mix. Their model also includes five pointers for planets. But there is no such dial pointers recovered which denotes the relative positions of the planets. But there is a 63 toothed gear in a major fragment which is the only proof for such planet pointers to exist within the mechanism.

Schematics of all the gears and shafts
Credit: Wikipedia Commons

   The mechanism is created for a viewer on Earth. This doesn’t explain whether the mechanism works as a geocentric or heliocentric planetary model. The probability is that it is geocentric because there is no evidence of any heliocentric planetary model in that time period.

   The mechanism is still not yet completely known. Still there are lots of hidden parts in this machine. Yet it makes us wonder about the knowledge of ancient world. This truly is an amazing historical marvel.