Giovanni Dondi's Astrarium, 1364

Giovanni Dondi's Astrarium, 1364
Museo Nazionale della Scienza e della Tecnologia Leonardo da Vinci di Milano

Reconstruction (1961-3) of the astrarium of Giovanni Dondi (1348-64)
Details. Maker: Luigi Pippa. Date: 1961-3.  Dimensions: height 98 cm, diameter 90 cm, weight 80 kg. Materials: iron, brass, copper.  Source: Museo Nazionale della Scienza e della Tecnologia Leonardo da Vinci di Milano. Licence: (CC BY-SA 4.0).

Supplementary images: faces for the sun (2), Mercury (3), Venus (4), Mars (5), and Jupiter (6). Dondi's drawing of the dial for Venus (7: Padova, Biblioteca Capitolare, Ms. D.39, f. 12v. Wikimedia: public domain). Leonardo da Vinci's drawing of a dial for Venus (8: Institut de France ms L: 92v. Wikimedia: Public domain)
Commentary. An ‘astrarium’ or ‘planetarium’ is an astronomical clock which provides a mechanical representation of the cyclic nature of all the main objects of the heavens in a single timepiece.
Astonishingly, the first documented example of such a device was completed (after 16 years’ work) in 1364, only about 60 after Europe’s very first mechanical clocks.* So remarkable was this accomplishment that its maker – a Venetian astronomer, philosopher, poet, and professor of medicine in Padua – was immortalized under the name Giovanni Dondi dall’Orologio (1318-1388).
Dondi’s Astrarium had seven faces, one each for the movements of the sun, the moon, and the five planets according to a Ptolemaic system (see video, 2:02-2:54 and images above). It also displayed the legal, religious, and civil calendars of the day. A single weight drove the mechanism, which was communicated to the faces by 107 moving parts.  
Contemporaries regarded it as little short of a technological miracle: as Giovanni Manzini of Pavia wrote in 1388, ‘Never was there invented an artifice so excellent and marvellous and of such genius’.  For centuries the astrarium attracted admirers from across Italy, including Leonardo da Vinci, whose drawings of the dials for Mars and Venus still exist.  
Fortunately, de Dondi also left a meticulous account of the design of the machine in a manuscript, which was much copied: twelve manuscript copies survive today (see video, 1:15-1:27). The clock itself was lost, possibly in the sack of Mantua in 1630, but the detailed written descriptions and numerous drawings have enabled several twentieth-century reconstructions of the astrarium, including those now on display in

* Giovanni’s father, Jacopo de Dondi, had taken a major step in the direction of the astrarium in 1344: he constructed the first known clock which combined the movements of the sun and moon with the zodiac, complete with geometrical figures designed to reveal at a glance the astrological aspects between the sun and moon.  His clock, destroyed in a fight between Padua and Milan in 1390, was rebuilt on a similar design in 1423, which can still be seen here.
Further information: Christophe Roulet, ‘Dondi’s astrarium, the eighth wonder of the world’, FHH Journal ( 24 October 2008).
Credits: Howard Hotson (May 2018)