Editing Astronomical clock (section)

=== Astrarium of Giovanni Dondi dell'Orologio ===

The [[Astrarium of Giovanni Dondi dell'Orologio]] was a complex astronomical clock built between 1348 and 1364 in [[Padova]], Italy, by the doctor and clock-maker [[Giovanni Dondi dell'Orologio]]. The Astrarium had seven faces and 107 moving gears; it showed the positions of the sun, the moon and the five planets then known, as well as religious feast days. The astrarium stood about 1 metre high, and consisted of a seven-sided brass or iron framework resting on 7 decorative paw-shaped feet. The lower section provided a 24-hour dial and a large calendar drum, showing the fixed feasts of the church, the movable feasts, and the position in the zodiac of the moon's ascending node. The upper section contained 7 dials, each about 30&nbsp;cm in diameter, showing the positional data for the [[Primum Mobile]], Venus, Mercury, the moon, Saturn, Jupiter, and Mars. Directly above the 24-hour dial is the dial of the [[Primum Mobile]], so called because it reproduces the diurnal motion of the stars and the annual motion of the sun against the background of stars. Each of the 'planetary' dials used complex clockwork to produce reasonably accurate models of the planets' motion. These agreed reasonably well both with Ptolemaic theory and with observations. For example, Dondi's dial for Mercury uses a number of intermediate wheels, including: a wheel with 146 teeth, and a wheel with 63 internal (facing inwards) teeth that meshed with a 20 tooth pinion.