This chapter interrogates one of the Museum’s prize objects, a late medieval English astrolabe, one of the earliest survivals of this type. Close analysis of the instrument’s specific design characteristics and engraved information is linked to recent scholarship on medieval astrolabe manufacture. Particular attention is paid to the often-overlooked back of the instrument, in particular its detailed calendar of Christian feast days, as a means of investigating the links between Christianity and scientific investigation, and between patrons, monasteries, and the universities in the medieval period.

Telling the time in medieval England was not always straightforward. A variety of timekeeping devices were in use, and a study of the astronomical and timekeeping instruments that survive from this period shows that many were portable and could have been carried around to tell the time. But were they? Or, were they made and used for other purposes? These questions run through much of the scholarship on these kinds of instruments. Examples of these instruments survive in museum collections, but it is difficult to determine how they were used, and for what purpose. This chapter is the result of that reconsideration of fundamental questions about the uses and users of astronomical instruments in medieval England. I argue that we should look again at the practical uses of some types of instruments, and consider whether some were carried around to tell the time, to be used for practical purposes alongside symbolic, teaching, and other functions. Instruments could be “ideas made brass” but they could also be of practical use, and I suggest that it was precisely this combination that may have made some instruments more important, or more common, in the period.