Astrolabes are problem solving instruments – they compute things such as the time of day according the position of the sun and the stars in the sky. Like a computer, you input information and then you receive output. They were typically made of brass and had a 6 inch diameter, although as we will see much larger ones were made.
This instrument is clear evidence of the links between the astrolabe and astrology. On one side is an astrolabe for a single latitude, and on the other an astrological volvelle, used to find the positions of planets and other celestial bodies, especially in relation to the traditional astrological houses.
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).