The heavens were a fascinating province for the medieval monk. Many looked up not just for obsecration, but also for curiosity and understanding. In this manuscript from St. Gall, Switzerland, a monk is depicted observing a heavenly object, but what this object is, it is now impossible to tell from the manuscript evidence alone. He appears to be using an optical instrument which he is holding to his eye and which is pivoting on some sort of a mount resembling the shaft of a column.
When I first saw this manuscript folio, I thought that the roundel was intentionally cut around to reveal some painted figuration on the next sheet. The medallion once depicted the Horologium nocturnum, an instrument whose graphical representation allowed the monks to calculate the night hours of the Divine Office. It seems, however, that the illustration, perhaps of a Northern constellation, was violently removed from the manuscript. The reason why the inside of the roundel appears black is that in the process of digitising the manuscript, perforations in the membrane are photographed against a black sheet placed underneath in order to avoid the confusion that might arise from overlapping surfaces.