The “Emperor’s Astronomy” (Petrus Apianus, 1495-1552) is one of the great masterpieces of sixteenth-century printing, and also one of the top-ten in my personal digital collection. I found the codex a couple of months ago, when I was looking for “volvelles” (or wheel chart, which is a paper slide chart with rotating parts used mainly in ancient astronomy treatises, introduced by Persian astronomer Abu Rayhan Biruni).
I’ll not extend on Petrus Apianus BIO, Wikipedia has a relatively detailed article here. As remarkable fact, Apianus became a favourite scientific of Emperor Charles V through his work and produced also some well known treatises like the “Cosmographicus liber” and other works with variations and studys of Pascal’s triangle, collections of volvelles, and the first known depiction of Bedouin constellation.
Regarding the “Emperor’s Astronomy”... Most of the Volvelles in the codex are used –based on Ptolemaic system- to provide a remarkably accurate graphical calculation of a planet’s position. There is even one for calculating the longitude of Mercury, which contains nine printed parts plus a complex hidden infrastructure to allow movement around four separate axes. Throughout the initial part of his book, Apianus gives detailed instructions for the operation of the volvelles, using as his examples the birth dates of the Holy Roman Emperor Charles V and his brother Ferdinand I, the dedicatees. But the most curious volvelle is used… for finding the hour of conception from the time of birth and the phase of the moon!!
The second part of the Astronomicum Caesareum deals primarily with lunar eclipses and five comets observed by Apianus in the 1530s. One of them is the one now known as Halley’s Comet. There are 93 known survived copies of this treatise around the world. In 1985 a copy of the Astronomicum Caesareum was auctioned for 80,000 dollars.
