Antikythera-Mechanism

often called the “world’s first analogue computer” since its discovery in the early 1900s from a shipwreck of the coast of the island of Antikythera. Currently, there are are 82 fragments, consisting of 30 eroded bronze gears, representing merely one third of its original presumed structure

It has been established that the wreck (and hence the mechanism) must have been from the first century BCE dated to 65 BC $\pm$ 1.5 years¹. The device is about the shape and size of a shoebox, with metal plates on the front and back faces displaying various dials, scales and inscribed Greek text as the outputs, while the other sides were wooden, featuring a knob or crank as the input.²

Front face of the mechanism

The front face of the mechanism featured one central dial with with two concentric rings, inferred to have pointers that tracked the motion of the five visible planets and the sun ³ =

• The inner Zodiac scale was divided into twelve sectors, each with thirty subdivisions, representing the motion of the heavenly bodies with reference to the fixed stars.
• The outer ring was the Egyptian calendar scale, divided into twelve 30-day sectors and a smaller thirteenth 5-day sector. This represented the Egyptian “civil” calendar, used from the third millennium BCE onwards, with three seasons of four months each, and five additional days at the end of the year that belonged to no month to account for the need of a leap year.

Why include an Egyptian calendar in a Greek mechanism

• as seen by the first century BCE writer Geminos, the Greeks did not have a specific word for “calendar”
• the Greeks used a lunisolar calendar =“reckoning the years in accordance with the Sun and the days and months with the Moon”⁴
• Jones (2017) ) asserts that the Greek calendar was a local institution. 
  • Archeological inscriptions reveal that every major Greek city had its own calendar, with different months and starting points, that reflected its religious and societal institutions. Additionally, officials often tampered with these calendars, adding or subtracting intercalary days or months as needed (pg. 66 - 69)

The Egyptian calendar, on the other hand, were much more robust and provided a consistent framework for dated observations. 

• The earliest Greek astronomer to use the Egyptian calendar in such a way was Hipparchus in the mid-second century BC⁵
• it was also used in everyday life, as seen in public inscriptions in Miletus around 109 BC⁶

Footnotes

1. Price 1959, pg. 61 ↩

2. Bitsakis and Jones, 2021 ↩

3. Jones 2017, pg. 57 - 59 ↩

4. Translation of Geminos, Introduction of the Phenomena VIII (7), is given in Evans and Berggren 2018, pg. 176 ↩

5. Seen in Ptolemy Almagest 3.1 ↩

6. Jones 2017, pg. 72 ↩