Antikythera mechanism
An ancient Greek geared bronze calculator, built around the second century BC, that predicted eclipses, lunar phases and planetary cycles.
Metonic cycle: A 19-year period after which lunar phases recur on the same calendar dates. The input gears encode this cycle; it synchronizes lunar months with the solar calendar on the dials.
Rhodes: The Dodecanese island famed for astronomy and engineering in the Hellenistic era. Its astronomical school and the wreck's route make it a leading candidate for the device's origin.
Valerios Stais: The archaeologist who in 1902 noticed a gear embedded in a corroded lump from the salvage. His observation turned a corroded fragment into the recognized machine we study today.
Planetary display reconstruction: Proposals for how the lost front dial showed planets, using epicyclic or pin-and-slot gearing. The largest unresolved question: no fragment confirms which planetary gearing the makers used.
Islamic astrolabe: Astronomical computing instruments of the medieval Islamic world, from the eighth century onward. Possible heir of Greek computational astronomy in the gap between the mechanism and clocks.
Saros cycle: A cycle of about 18 years, 11 days, after which solar and lunar eclipses repeat. The rear spiral dial predicts eclipses by counting out this cycle.
Archimedes: Syracusan mathematician and engineer, killed in 212 BC, credited with building geared planetaria. Cicero describes his spherical planetaria, the closest known ancestors of the mechanism's tradition.
Derek J. de Solla Price: Historian of science who published the first full gear-train reconstruction, 'Gears from the Greeks', in 1974. His radiographic work established that the fragments belonged to one complex geared computer.
Olympiad dial: A subsidiary dial tracking the four-year cycle of Panhellenic games, identified in 2008. Its discovery implies a civil and sporting function beyond pure astronomy.
Astronomical clock: Medieval European clockwork showing solar, lunar and calendrical motion, from the fourteenth century. Their gearwork was long thought unprecedented; the mechanism shows the lineage is far older.