A bit of background
Astrolabes have been around for a thousand years, but it was not until the 16th Century that the Universal Astrolabe was introduced.
The Planispheric astrolabe requires a plate for each location in which it is to be used. This means that the instrument could become quite thick and bulky with the library of plates stored within it. Also, some problems are expressed in celestial latitude and longitude, which is not something that instrument can handle. Two scholars, Gemma Frisius and Juan de Rojas y Sarmiento, came up with different ways to make an instrument which covered more bases. This was based on the work of al-Zarqalluh in the 11th century, from whom the name Saphea Arzachelis is derived. It is Gemma Frisius’ version that we have here.
This manual is as complete as I can get it for now but could use some beefing up, especially concerning coordinate system translations. I could use some help here – is anyone knowledgeable about this stuff?
The instrument is very usable for certain functions; please read through the ‘how to use it’ section. It also has a planispheric astrolabe on the other side, which can be used for 90% of the functions of my regular planispheric (it is missing the Equation of Time curve and shadow square, simply because there is nowhere to put those here).
With all that said:
1: A description of the Saphea Arzachelis, with explanations of the different coordinate systems
2: How to use it (to the best of my knowledge)
References:
‘The Astrolabe’ by James E Morrison, 2007 (I have the actual book, but a cut-down part of the chapter on Saphea Arzachelis is presented here)
‘The Planispheric Astrolabe’, National Maritime Museum Greenwich, 1985
Document history
version 0.1: July 2023