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The Encyclopedia of Horology

Astronomical clock (planetarium-clock) reconstruction · Italy (original); reconstructions built in Italy and England

Dondi Astrarium (modern reconstruction)

Verified

Giovanni Dondi's original astrarium, completed after sixteen years' work in 1364, displayed the time, calendar and the positions of the sun, moon and five known planets on seven separate dials driven from a single weight, using around 107 moving parts, and was regarded by contemporaries as an extraordinary technical achievement; the original itself does not survive, with its last documented sighting recorded in 1529. [2](https://www.cabinet.ox.ac.uk/giovanni-dondis-astrarium-1364)

Technical facts

Original display
Seven dials for the sun, moon and five classically known planets, plus calendar and feast-day information, per Dondi's treatise
Reconstruction (Pippa, 1961–1963)
Approximately 98 cm high, 90 cm diameter, 80 kg, built in iron, brass and copper

Historical significance

  • Giovanni Dondi's original astrarium, completed after sixteen years' work in 1364, displayed the time, calendar and the positions of the sun, moon and five known planets on seven separate dials driven from a single weight, using around 107 moving parts, and was regarded by contemporaries as an extraordinary technical achievement; the original itself does not survive, with its last documented sighting recorded in 1529. [2](https://www.cabinet.ox.ac.uk/giovanni-dondis-astrarium-1364)
  • Because Dondi left a detailed technical treatise describing the mechanism's construction, later scholars were able to build working reconstructions from his own description; the best-known is Luigi Pippa's 1963 reconstruction held in Milan, and a separate reconstruction project was carried out in England by Thwaites and Reed between 1961 and 1974. [3](https://www.museoscienza.org/en/collection/objects/giovanni-dondi-astrarium) [4](https://collection.sciencemuseumgroup.org.uk/objects/co964/winding-mechanism-for-reconstruction-of-dondis-astrarium-1961-1974)
  • Researchers should always describe any surviving astrarium as a reconstruction, never as the original 1364 mechanism, and should specify which reconstruction (Pippa's Milan example or the English Science Museum Group project) a given claim refers to.

Sources & references

  1. Museo Nazionale della Scienza e della Tecnologia Leonardo da Vinci, Milan, published collection record
  2. Science Museum Group Collection, published object records for the English Dondi clock reconstruction

Where sources disagree, the disagreement is stated rather than resolved silently.