The manuscript Ambrosiana H 57 sup. includes two texts on the astrolabe, Philoponus’s as well as an anonymous one from perhaps the late 13th century (though this copy is dated 14th century). Along with these texts are a couple Ptolemaic works and Theon of Alexandria’s “Commentarium paruum in Ptolemaei canones.” The manuscript itself is lovely with amazing illuminations. I want to pause on two of these illuminations.
On the first page of the manuscript, the beginning of Theon’s commentary, is an amazing illustration of a monk standing under a star-strewn sky, using an astrolabe to determine the altitude of a planet (perhaps the moon), while another kneels in front of him taking notes. What makes this illustration so interesting, to me, is the astrolabe. Although the Byzantine scholars produced a number of texts on the astrolabe (two in this manuscript), only a single instrument survives. This surviving astrolabe, now in Brescia, dates from 1062 (see my post, The Brescia Astrolabe). Given the near absence of surviving instruments, I always get excited when I see any concrete reference to using an astrolabe in the Byzantine context.
Much later in the manuscript we see another illustration of another monk using an instrument to determine the elevation of a celestial object. In this case, it looks like it was meant to be a triquetum.
That’s all. Just two illustrations of Byzantine scholars using astronomical instruments.