Jost Bürgi, a Swiss watchmaker, builder of scientific instruments, astronomer and astrologer, worked in the service of Emperor Rudolph II in Prague. He teamed up with the jeweller Antonius Eisenhoit to build several armillary spheres like this one in gilt bronze, dated 1580. An armillary sphere illustrates the Greeks' Earth-centred vision of the universe. The moving sphere shows the constellations and is complemented by a perpetual calendar cleverly designed to indicate leap years. Bürgi's work spurred Tycho Brahe and Johannes Kepler to build astronomical clocks. A masterpiece of German Renaissance metalwork, this celestial sphere was in the collections of the Academy of Sciences for a long time before entering the Musée des arts et métiers in the mid-19th century.