From Globes to Celestial Maps

Illustrating the Phaenomena plugs with one erudite and fell swoop a hitherto glaring gap in our knowledge of cartography, namely its history from Antiquity to about 1500, just as the introduction of the printing press began to change everything. Where Deborah Warner, in her excellent 1979 study The Sky Explored: Celestial Cartography 1500-1800, starts, Dekker wraps up.

Combining textual evidence with unparalleled knowledge of the material culture and a complete command of research conducted over the past 120 years or so, the author sets out to write the unwritten history of cartography before 1500. Boldly stating that “for a proper evaluation it is essential to establish our material heritage of manuscript maps and globes” (p. vi), this is precisely what she does over the subsequent 460 pages. As Dekker’s study illustrates, “the introduction of the moving sphere as a model for understanding the celestial phenomena caused a great breakthrough in scientific thinking about the structure of the world” (p. 432).

Globes are basically constructed according to two principles: descriptive and mathematical. As Dekker shows, the ability to construct descriptive globes, popular for their ability to help explain the cosmos without in-depth knowledge of spherical astronomy, has existed as early as the fourth century b.c.e., even if no examples survive. Equally by deduction, in this case based on an in-depth study of the comparatively large corpus of maps in medieval manuscripts, the author can show the existence of celestial maps in antiquity. The second part of Dekker’s study examines the existence of globes and maps based on mathematical principles, which had been available since Hipparchus’ discovery of precession in the second century b.c.e. Until about 1500, all globes and maps in this tradition, whether European or Islamic, were based in some way on Ptolemy’s Almagest, itself based on the now-lost star catalogue of Hipparchus.

Elegantly and convincingly navigating between Antiquity, the European Middle Ages (yet again shown beyond doubt to be anything but “dark”) and the Islamic World in its narrative, this book also provides us with a detailed catalogue of 16 extant globes made before 1500 and 40 celestial maps, with a detour via the celestial ceiling of Qu.ṣayr ^cAmra in modern-day Jordan. Never before has such varied material been studied collectively; never before has it been possible to prove that globe-making was for centuries the most significant stimulus in the development of celestial cartography.

This study required encyclopedic knowledge of the sources and thorough understanding of the underlying mathematical principles required to design and construct these maps and globes. Dekker’s analysis is precise and to the point, never falling into the trap of projecting modern principles backward in time.

Illustrating the Phaenomena is yet another proof of Dekker’s rare gift to bring clarity to complex subjects. It is an eminently readable, concise overview that will doubtlessly become a standard reference work for scholars and interested lay people alike for many decades to come.

Silke AckermannUniversity of Oxfordsilke.ackermann@mhs.ox.ac.uk