Lauren Caldwell's tribute to Giovanni de' Dondi's 1364 Il Tractatus Astarii, the first famous Astrarium, which is a mechanical planetarium that mimics the paths of the stars and planets. In other words, it's an astronomical clock Archimedes used a primitive model, but the first real working astrarium clock is credited to de Dondi. The backpiece here is the Mercury Wheelwork.

Used with permission from SCIENCE INK by Carl Zimmer. Published by Sterling Publishing © 2011