Antikythera << AN tee kee theer uh >> mechanism is a mechanical device discovered in an ancient Greek shipwreck . The device’s remains consist of 82 bronze fragments. Science historians reconstructing the Antikythera mechanism determined that the device was a sophisticated astronomical computing machine. They believe the mechanism is the world’s oldest mechanical computer .
Divers harvesting natural sponges discovered the ancient shipwreck in 1900 off the coast of Antikythera, an island in southern Greece. Researchers recovered the device while investigating the shipwreck in 1901. The ship had carried a rich cargo of statues and art glass when it sank around 60 B.C. Over several decades, curators cleaned and science historians attempted to reconstruct the mechanism. In the 2000’s, they examined the device using X rays and computed tomography (CT) scans. This work enabled them to view inscriptions hidden behind surface layers of corrosion on the mechanism and learn how it was constructed. They could then create a three-dimensional replica of the device to understand how it functioned.
In its original form, the device was a wooden box about 12 1/2 inches (32 centimeters) long, 8 inches (20 centimeters) wide, and 4 inches (10 centimeters) deep. It held at least 30 bronze gears inside. Bronze plates, with Greek inscriptions explaining the features of the machine, covered most of the device. The front face had a circular representation of the zodiac divided into 12 sections of 30 degrees each. The zodiac is a set of 12 constellations used to mark the sun’s yearly cycle of movement against the backdrop of stars.
Function.
The Antikythera mechanism functioned as a hand-cranked clockwork computer. It tracked the movement of heavenly bodies according to two different calendars .
A knob turned gears that moved a small ball, representing the sun, through the signs of the zodiac. Another ball representing the moon moved across the zodiac, marking a lunar month. This ball, half silver and half black, turned on an axis, simulating the moon’s changing phases. Historians believe that the motions of other planets known to the ancients were also displayed. However, this part of the mechanism was not preserved.
Surrounding the signs of the zodiac was a calendar scale divided into the months and days of the ancient Egyptian calendar. Greek astronomers often favored the Egyptian calendar in their work, as the years were of uniform length at 365 days. The date in the Egyptian year was indicated by the moving sun ball.
On the back face, a spiral dial indicated the months of a Greek calendar. In this calendar, there are 12 years of 12 months and 7 years of 13 months spread over a cycle of 19 years, known as the Metonic cycle. This cycle is named for Meton, a Greek astronomer who lived in the 400’s B.C. Each major city in Greece had its own Metonic calendar with different names for each month. The month names inscribed on the Antikythera mechanism suggest that the device was made for use at Corinth or one of its colonies.
The Antikythera mechanism also had a panel on the lower back face that could be used to predict lunar and solar eclipses . It could predict the month and even the time of day when such eclipses occurred. These predictions were based on an eclipse cycle developed by the Babylonians , called the Saros.
Origin.
Science historians believe the Antikythera mechanism was built some time after about 205 B.C. The eclipse predictor would have been most accurate for an 18-year Saros cycle that started in 205. But the device could have been built some decades later. To researchers, the astronomical knowledge demonstrated by the Antikythera mechanism is not surprising, as these aspects of astronomy were well understood in the period. However, scholars find the engineering of the device remarkable. A few ancient Greek texts describe mechanical devices utilizing gears. But the machines discussed in these texts are very simple, such as an odometer to indicate how far a chariot has traveled. No one would have believed that a machine as complex as the Antikythera mechanism could have been possible on the basis of the surviving ancient sources about gears.
Scholars believe that similar machines were built both earlier and much later than the Antikythera mechanism. For example, the Roman author Cicero attributes such a machine to Archimedes , a Greek mathematician, physicist, and mechanical engineer who lived from about 287 to 212 B.C. The astronomer Ptolemy mentions a similar device in texts dated to about A.D. 150. Scholars believe the tradition of making devices like the Antikythera mechanism lasted about three and a half centuries. But scholars believe that devices as sophisticated as the Antikythera mechanism were uncommon, and would have been highly valued.
