Giovanni Dondi's astrarium

Giovanni Dondi dell'Orologio was born in Chioggia in 1318. In 1342, his family moved to Padua, where his father introduced him to the study of science, and to medicine in particular.

In 1354, Dondi became a professor of medicine, and then of astrology and astronomy, at the University of Padua. From 1362 to 1365, Dondi taught at the University of Pavia, which was founded by Charles IV, Holy Roman Emperor, on April 13, 1361.

The University patron, Galeazzo Visconti, coerced students in the State of Milan to study there.

During his time in Pavia, Dondi also served as astrologer and physician to the prince.

After having lived in Florence, Rome, and Padua again, Dondi settled in Pavia in 1379, when Visconti called on him to look after his son.

From 1379 until his death, he regularly taught in Pavia, as a royal physician and astrologer rather than professor, receiving an annual salary of 2,000 florins.

He went to look after Prince Antonietto Adorno, the 6th Doge (duke) of Genoa, the same citywhere it is said that he died in February 1389.

Giovanni Dondi's Astrarium puts Ptolemaic theory into practice.

In the Ptolemaic system, the Earth is at the center of the (then-known) universe, while so-called fixed planets and stars move around it in a determined direction, regardless of their proper motion.

It was built as an instrument to map the position of celestial bodies, which were believed to determine humankind's destiny.

The original astrarium was built by Giovanni Dondi in the second half of the 14th century.

The precise period is a bone of contention. It was first dated as 1348–64, then subsequently that period was refuted by new arguments and moved by around 20 years to 1365–80.

The new date range, in any case, still places the astrarium at the pinnacle of medieval horology.

Reconstruction of the astrarium was possible thanks to Giovanni Dondi's manuscript "Tractatus Astrarii," in which he described the design and its construction phases.

This treatise is one of the first technical and scientific works of its kind and is stored in the Capitular Library of Padua.

In the treatise, Dondi gives a detailed description of all the designs and the construction phases, as well methods for setting the various faces, reading devices, and instructions for the maintenance of the mechanism.

The reconstruction of Giovanni Dondi's Astrarium was carried out between 1961 and 1963 by Luigi Pippa, a Milanese clockmaker, with the financial support of Innocente Binda.

The reconstruction was completed for the National Museum of Science and Technology in Milan.

The astrarium still belongs to its collection.

The astrarium is a very complex mechanism that indicates the position and movement of celestial bodies. It consists of 9 faces: 7 on its upper section and 2 on its lower section.

On the upper section, 5 faces indicate the annual movement of the then-known planets (Mercury, Venus, Mars, Jupiter, and Saturn), one marks the movement of the sun, and the other, that of the moon.

On the lower section, there is a face for the time and a face to predict lunar eclipses, also known as the node line.

In the center of the astrarium is the calendar wheel, which completes one turn every year. This indicates the day of the week, the name of saints, the dominical letter, and the length of the day in hours and minutes.