Modelling the movements of the heavens
Commentary
Image. Astronomical clock, Old Town Square, Prague. Credits: Andrew Shiva, 28 July 2013 / Wikipedia / CC BY-SA 4.0
Commentary. Installed in 1410 by clock-makers Mikuláš of Kadaň and Jan Šindel, the famous Pražský orloj is reputed to be the third oldest astronomical clock in the world, and the oldest still functioning.
The first video (below) provides a fast-motion animation of the movement of the clockface: in little more than a century after the invention of the mechanical clock, the desire to reproduce the movements of the heavenly bodies had produced clock faces far more complicated (although also far less accurate) than modern clocks. In addition to the legend provided by Image 2, an account of its many functions can be found here and here.
The second video provides a detailed account of the functions of the Prague clock. In this video, Christopher Scott Vaughen draws on the detailed description available here and the graphic simulator available here.
The third video below provides some information on the clock in Hampton Court Palace, designed for Henry VIII by Nicholas Krazter and installed in 1540. Some 15 feet (4.6 m) in diameter, the clock face is composed of three separate copper dials revolving at different speeds. Together these display the hour, month, day of the month, position of the sun with respect to the zodiac, number of days since the beginning of the year, phase of the moon, age of the moon in days, and hour when the moon crosses the meridian. The last of these pinpoints the highwater mark at London Bridge, and thus provides a guide for the best time for travel by boat into London.