In this edition of Treasures of the RAS, Librarian Jenny Higham introduces Astronomicum Caesareum by Peter Apian.
This gorgeously coloured book was published in 1540. This book was produced for Charles V, Holy Roman Emperor, and only a few were printed and then coloured by hand. It contains many elaborate moving paper discs, which can be used as instruments to calculate the positions of the planets.
The calculations were on the geocentric system of Ptolemy, who assumed that the planets, moon and Sun all orbited the Earth. A few years later Copernicus proposed the heliocentric theory, which made Ptolemy's system obsolete.
The Latin title is Astronomicum Caesareum (sometimes given as Caesarium), which translates as The Astronomy of the Caesars (Emperors).