The celestial globe represents the eighth crystalline sphere in the model of the universe according to the theory put forward by Ptolemy around 150 A. D. It supports the Heavens. This near perfect system, which accounted for essentially all of the movements described by the Heavenly Bodies, and which confirmed mankind in its geocentrism, remained unchallenged until Copernicus.

The astronomer’s celestial globe is an instrument upon which, by means of longitudinal and latitudinal coordinates, the user marks on a sphere the stars he observes or discovers. On this sphere are indicated the principle circles of coordinates, viz.: the colures of the equinoxes and solstices passing through the polar axis and, perpendicular to these, the equator, the tropics and the polar circles; finally, the ecliptic circle, tangential to the tropics and inclined by about 23 1/2º with respect to the equator. The astronomer then groups the stars into constellations. The twelve main ones, those of the zodiac, are aligned along the ecliptic. The constellations are shown inverted with respect to how the observer sees them from the Earth, represented as a fixed point at the centre of the sphere.

The first celestial globes were made of painted wood or engraved metal. It was only with the Renaissance and the invention of printing techniques that it became possible to reproduce globes made of paper gores pasted together thereby allowing this scientific activity to spread. Modern celestial globes thus contain the sum of knowledge acquired over three millennia. The first celestial globe is said to have been made by Eudoxus of Knidos ( around 360 B. C. ). Later, Cicero mentions the celestial globe of Archimedes which Marcus Claudius Marcellus, conqueror of Syracuse, brought back as trophy together with the great scientist’s globe clock and offered to the Temple of Vesta in Rome. In the second century A. D., Ptolemy explained how to construct a celestial globe ( Syntaxes, 8. 3 ). He states that a well-made globe must show the stars in yellow and red against a dark background and that stars of the same constellation must be connected together by lines and not incorporated into a figure which hindered calculation.

Although it does strictly meet Ptolemy’s scientific aims, the first celestial globe in this exhibition ( cat. no. C1 ) nonetheless shows all the constellations known in Antiquity. It is a unique testimony of astronomical science at this time since it is the third celestial globe preserved from Antiquity.

A symbol of knowledge but also of power, the celestial globe became an attribute of Roman Emperors, emblematic of their dominion over a universal empire. This symbol was taken over by the Holy Roman Emperors who added a cross above the sphere. No major figure of astronomy followed Ptolemy and the science of the Classical World was recorded in writing and transmitted by Byzantine scribes. But the new Christian religion was wary of this branch of science which it considered too close to astrology and paganism. It was to be Arab scholars, through the Islamic conquests, who revived astronomy starting in the VIII th and IX th centuries. The great Classical authors such as Euclid, Aristotle and Ptolemy were translated and made widely available and important cultural centres flourished from Spain to Persia. Some astronomers such as Albumazar ( Abu Mashar 787-886 ) or Al-Sufi ( 903-986 ) became famous in Christian Europe. A dozen brass celestial globes, often set with silver stars, date from the great age of Islamic astronomy between 900 and 1300.

Unrelated to the Islamic world, the first Western maps of the Heavens or planispheres begin to appear in the IX th century. They seem to derive directly from the Late Empire. Throughout the Middle Âges, these diagrams were copied from abbey to abbey by anonymous scribes. In Reims, Gerbert d’Aurillac ( 946-1003 ), later Pope Sylvester II, made use of different instruments in his teaching of astronomy and invented a wooden celestial globe painted with circles. It was in Spain that astronomy passed from the Islamic world to the West through numerous exchanges among Arab, Jewish and Christian scholars. In Toledo, from 1140 to 1185, Gerard of Cremona tirelessly translated the great Classical authors, especially Aristotle and Ptolemy, from Arabic into Latin. The first Western map of the Heavens which includes the stars and their coordinates, the Vienna Manuscript, dates from around 1440 and is kept in the collection of the Österreichische Nationalbibliothek in Vienna. Although the origins of this map are unknown, it served as a source for the first Western celestial globe in engraved metal executed in 1480 by the scientific instrument-maker Hans Dorn, now kept at the Jagellon University in Krakow. The same unattributed source inspired the author of the engraved brass globe of around 1525 ( cat. no. C2 ), made just before the wide dissemination of printed maps and celestial globes which was radically to alter astronomy and the production of celestial globes in general. The first printed map of the Heavens is Albrecht Dürer’s of 1515 and the first globe was made by Johann Schöner around 1533 in Nuremberg, followed by the one made in 1537 by Gemma Frisius in Louvain. Whereas the production of printed globes underwent considerable development during the XVI th and XVII th centuries, in particular in Holland and then in Italy, celestial globes in gilt bronze or other precious materials remained extremely rare.

The advantage of metal over paper is that it more closely approaches Ptolemy’s model of the crystalline sphere by ingeniously cutting out portions of the two hemispheres such that the Earth can be distinguished at the centre of the globe while the outlines of the constellations are also visible. This delicate operation which requires great skill is admirably illustrated by the celestial globe bearing the arms of the di Pretella family and carried by Hercules attributed to Vincenzo de’ Rossi ( cat. no. C3 ) as well as by the globe attributed to Petrus Aspheris ( cat. no. C4 ). Another superb example of a fretwork celestial globe is to be found on the globe clock by Pierre de Fobis ( cat. no. S2 ).

The three German Renaissance globe clocks included in this exhibition are also superb examples of engraved celestial spheres ( cat. nos. S3, S4, S5 ), their bronze surfaces silvered to make the constellations more legible. More delicate materials such as ivory allow artists to make globes for more decorative or didactic purposes ( cat. nos. C6, C7 ). The most precious celestial globe in this section of the exhibition, however, is the one executed around 1600 in rock crystal ( cat. no. C5 ). Material and transparency make it the most perfect illustration of Ptolemy’s crystalline sphere.