What Was The Number Of Faces On Giovanni Dondi Dell'orologio's Astrarium? [new]

While often not counted as an outward "face" in the same sense as the planetary dials, the lower section also contained a large . This internal component tracked the day of the week, religious feast days (saints' days), and the length of each day throughout the year.

Here is the detailed breakdown of that figure.

It had 7 main dials , but those dials contained a total of 107 individual hands and indicators to track the complex motions of the Moon, Mercury, Venus, Mars, Jupiter, and Saturn according to Ptolemaic astronomy. While often not counted as an outward "face"

Because Dondi wasn’t trying to tell time . He was trying to in real-time, gears, and pointers. In the geocentric model, each planet moves on a series of circles (deferent, epicycle, equant). To know a planet’s true position in the sky, you need to know several simultaneous motions:

The Astrarium had 107 faces (i.e., separate moving pointers). It had 7 main dials , but those

The breakdown by dial is as follows:

Built over a period of 16 years, the Astrarium was considered a mechanical miracle of the Middle Ages, utilizing 107 moving parts to synchronize these various astronomical and temporal displays. In the geocentric model, each planet moves on

This face often included an astrolabe-type dial to show sidereal time and the sun's position. The Moon: Dedicated to tracking lunar movement.

Each of these required a separate, concentric pointer or "face" on the dial. Dondi considered each distinct moving index a vultus (face). So, a single dial for Mars might have:

To a modern observer, this seems absurdly redundant. Why not just one hand per planet?