The Antikythera mechanism was an ancient Greek astronomical device created between 205 and 60 BCE. It is considered the first known analog computer because it used complex gearing to calculate and predict astronomical cycles and the movement and positions of celestial objects. It also contains the first known set of scientific dials, which were used to show the positions of the moon, sun, and planets as well as the timing of various astronomical cycles. The Antikythera mechanism combines cycles from Babylonian astronomy with ancient Greek astronomical theories and mathematics to form a device of amazing complexity.
The Antikythera mechanism was discovered in 1901 in the wreckage of a trading ship that sank in the Mediterranean sea near the island of Antikythera. When it was discovered the mechanism had been underwater for 2,000 years and the bronze had corroded and turned green. Though the Antikythera mechanism was discovered in 1901, scholars were unable to determine its purpose until the 1970s, when X-ray imaging was used to discover that the device depicted the motion of celestial bodies. Further research in 2005 using CT-scan revealed more about its inner workings and inscriptions. Using the scans as well as the Greek inscriptions covering the device researchers have been able to recreate how the gearing of the device may have functioned.
The Antikythera mechanism is made of bronze and would have been around the same size as a shoebox. The fragments of the mechanism that were recovered contained more than 30 gear wheels, making it the only known device with such complex gear mechanisms before the clocks created in medieval times. The device contained a dial on the front, depicting the position and movement of the sun, moon, and planets as well as the date. Several dials on the back of the device show various astronomical cycles. The front and back faces of the mechanism are covered in Greek inscriptions, which enabled researchers to determine the purpose of the various parts of the device and which also give clues to the missing sections. The device was probably powered by turning a knob on the side (not recovered) which connected to the main gear wheel. This wheel represented one solar year and had various other trains of gears connected to it.
The front dial of the Antikythera mechanism contained hands that show the positions of the sun and moon as well as a rotating ball, that displayed the lunar phase. It also contained pointers for the positions of five planets visible to the naked eye: Mercury, Venus, Mars, Jupiter, and Saturn, but also planets have not survived. The dial also contains rings showing the Zodiac and the Egyptian calendar, the latter of which is a 365-day calendar consisting of 12 months of 30 days with an additional 5 days. The gears involved in recreating the motion of the moon are highly sophisticated and mimic the subtle variations in the moon’s motion. The gearing for the planets, though very little of it has survived, was likely also extremely complex and involved epicycles, smaller gears, or circles that rotate around a larger one, which was key to the Greek’s understanding of the planet’s motion relative to earth.
The two large dials at the back of the Antikythera mechanism contain pointers that rotate in spiral grooves. The upper of these two dials depicted the 235 lunations, in the Metonic cycle. A lunation is the time it takes the moon to complete one whole cycle of its phases (for example going between two full moons). The Metonic cycle lasts 19 years and aligns the phases of the moon to the days of the solar year. A smaller dial inside this dial likely contained the Callippic cycle, a 76-year cycle consisting of 4 Metonic cycles that match the phases of the moon to not only the same day but also the same hour of the solar year. Another small dial contained a 4-year cycle showing when the four Panhellenic games, as well as several more local games, should occur. The Panhellenic games were athletic events where the various Greek city-states competed against each other. These included the Olympic, Pythian, Nemean, and Isthmian games.
The lower large dial on the back of the Antikythera mechanism showed the months when a solar or lunar eclipse was likely to occur. This was based on the Saros eclipse cycle, a cycle lasting 18 years and 11 and ⅓ days where the earth, moon, and sun have roughly the same positions relative to each other. The Saros eclipse cycle is used to predict the timing of eclipses because eclipses repeat at the same points in the cycle. A smaller dial inside this dial depicted the Exeligmos cycle, a cycle lasting 54 years and 34 days that consists of three Saros cycles and after which the eclipses will be viewable from the same geographic region on earth.
The Antikythera mechanism was extremely sophisticated for its time, combining many astronomical theories with complex gear mechanisms. However, it is unknown exactly where the Antikythera mechanism was made or who it was made by. Some theories are that it was made on the island of Rhodes by the philosopher Posidonius or the astronomer Hipparchus. There are thought to have been many mechanical astronomical devices created in ancient Greece and Rome, but the Antikythera mechanism is the only one of these that is known to have survived to the present day. The Antikythera mechanism reflects the Greek’s view that nature works according to set rules and patterns, an idea that is the basis of the modern scientific viewpoint. The Antikythera mechanism can be viewed at the National Archaeological Museum in Athens.
These interesting videos demonstrate a computer model of how the Antikythera mechanism may have worked: https://www.nature.com/articles/s41598-021-84310-w#Sec150
About the Author
Marcella is a Junior at Northwood High School who is interested in a career as a Conservation Biologist. She enjoys reading, playing the piano, and being outside.
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