Description
Giovanni de Dondi, Doctor of medicine, logic and astronomy at Padua University, designed and made this astronomical clock, or 'planetarium' during the years 1348 to 1364. By recording minutes as well as hours the clock was 200 years ahead of its time, whilst Dondi's mechanism for taking account of the slightly elliptical movement of the moon would not be replicated for 400 years and the perpetual calendar for Easter for 500 years.

Sadly the original clock has been lost, believed destroyed when the French attacked the monastery of San Juste in Spain during the Peninsular Wars of 1809. Fortunately for posterity Giovanni de Dondi did what many scientists fail to do - he wrote and illustrated a complete description of his planetarium with detailed instructions for its construction and set-up. Several copies of his manuscript, written in Medieval Latin, are preserved in libraries in various parts of the world.

A private translation of the Latin manuscript into English was made by the horological historian G H Baillie in the 1930s, but not published until 1974. This almost full size replica was built using Baillie's translation.

The dials indicate the motions of the planets, this being defined by the Ptolemaic conception (that is, a model of the Universe with the Earth at the centre), and calculated using the Alfonsine Tables of astronomical observations.

The first side of the planetarium has the Horary Sphere with two side tables indicating the times of sunrise and sunset at Padua. Above it is the Primum Mobile, or the Dial of the Sun.

To the right of the Horary Sphere is the Dial of Venus with the Fixed Feasts below it. This is followed by the Dial of Mercury, with below the Moveable Feasts fixed by the date of Easter. Then next right is the Dial of the Moon; note the oval gearwheels and below the Dial of the Dragon's Head and Tail or the Nodes. This rotates once in 18 years 7 months 14 days. Then following to the right of the Dial of the Moon are
the Dials of Saturn, Jupiter and Mars in that order.

This planetarium and the replica of the near contemporary astronomical clock by Richard of Wallingford (standing in the Main Gallery next door) represent the two styles of clockmaking in the early 14th century. The Dondi Planetarium was made by a scientific instrument maker while the Wallingford clock was made in a more traditional manner by a clocksmith.
22/03/2023
Created by: Guey-Mei Hsu on 22/03/2023