| Summary: | Astrolabes serving all latitudes are very rare. This recently rediscovered sixteenth-century Spanish example raises a host of questions which can only be addressed by considering all other such instruments and the few available textual sources. The instruments can all be traced back, not always directly, to an invention of the eleventh-century Andalusian astronomer Ali ibn Khalaf, preserved in the Old Castillian Libros del Saber de Astronomía of King Alfonso X. The design of this particular astrolabe and the engraving on it are investigated in detail, and the as yet unidentified maker is associated with the circle around Juan de Herrera, architect of the palace-monastery of San Lorenzo de El Escorial.
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