Astronomical clocks
During the 11th century in the Song Dynasty, the Chinese astronomer, horologist and mechanical engineer Su Song created a water-driven astronomical clock for his clock tower of Kaifeng City. It incorporated an escapement mechanism as well as the earliest known endless power-transmitting chain drive, which drove the armillary sphere.
Contemporary Muslim astronomers also constructed a variety of highly accurate astronomical clocks for use in their mosques and observatories, such as the water-powered astronomical clock by Al-Jazari in 1206, and the astrolabic clock by Ibn al-Shatir in the early 14th century. The most sophisticated timekeeping astrolabes were the geared astrolabe mechanisms designed by Ab Rayhn Brn in the 11th century and by Muhammad ibn Abi Bakr in the 13th century. These devices functioned as timekeeping devices and also as calenders.
The most sophisticated water-powered astronomical clock was Al-Jazari's castle clock, considered to be an early example of a programmable analog computer, in 1206. It was a complex device that was about 11 feet high, and had multiple functions alongside timekeeping. It included a display of the zodiac and the solar and lunar orbits, and a pointer in the shape of the crescent moon which travelled across the top of a gateway, moved by a hidden cart and causing automatic doors to open, each revealing a mannequin, every hour. It was possible to re-program the length of day and night everyday in order to account for the changing lengths of day and night throughout the year, and it also featured five robotic musicians who automatically play music when moved by levers operated by a hidden camshaft attached to a water wheel. Other components of the castle clock included a main reservoir with a float, a float chamber and flow regulator, plate and valve trough, two pulleys, crescent disc displaying the zodiac, and two falcon automata dropping balls into vases.
Astrolabes were used as astronomical clocks by Muslim astronomers at mosques and observatories.
The face of the Prague Astronomical Clock (1462)
The astronomical clock of St Albans Abbey, built by its abbot, Richard of Wallingford