Planet Disk, 15th century
This set of paper instruments was invented in the late 1450s to compute the positions of the planets without having to consult bulky sets of astronomical tables. The inner disk of vellum rotates around the center, representing the epicycle according to Ptolemy’s planetary theory. The pivoting pointer, also of vellum, marks the varying distances, numbered 1, 2 ... 5 of the epicycle from the Earth. Each planet requires its own set of circles and pointers. As can be seen by from the mark at the lower right, this disk is for the planet Jupiter.
[Ms. 1479, fol. 3r]
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