Characteristics and Typologies of Medieval Astronomical Tables

Abstract

INTRODUCTIONIn his Histoire generale et particuliere de l'astronomie (Paris, 1755), Pierre Esteve, member of the Royal Society of Sciences at Montpellier, reported:Alphonse X, Roi de Castille , employa beaucoup de richesses & de soins pour avancer cette science [l'astronomie]. Il fit assembler les plus habiles astronomes que le siecle avait produit ; leurs observations particulieres & celles de l'antiquite qui leur etoient connues , leur servirent a corriger les tables de Ptolomee : ils en construisirent de nouvelles , qui representoient plus exactement les mouvements du ciel. Ces tables furent nommees Alphonsines , du nom du Roi qui avait preside a tout l'ouvrage.1In this passage Esteve made a crucial remark. As was the case with many other sets of tables before them, the Alfonsine Tables compiled in Castile under King Alfonso (thirteenth century) had a dual origin: they were the result of new observations and they were built on previous material, mostly in tabular form.Because they present information in a condensed form, tables also played a fundamental role in the transmission of scientific knowledge. In the particular case mentioned above, the Castilian Alfonsine Tables contributed decisively to the dissemination in Christian Europe of a long tradition of Arabic astronomy. As a matter of fact, during the Middle Ages astronomical tables were probably the most efficient way to transmit mathematical astronomy whose goal was the computation of astronomical events.Astronomical tables are very frequently found in scientific miscellaneous manuscripts, many of which are entirely made up of tables. Despite their apparent uniformity, and for some the perception is that they all look alike, tables respond to a great variety of astronomical issues. In principle, they are intended to be 'user-friendly', that is, astronomical phenomena can be precisely computed without requiring the user to solve problems in trigonometry. In general, the tables include a selection of values arranged in columns for various astronomically significant functions, and all that is needed is interpolation between entries in the table and arithmetic rules for combining entries from different columns in the table. In many cases, astronomical tables were grouped in consistent sets allowing astronomers to solve most of the problems of medieval astronomy.The astronomical tables considered in this paper were compiled from about the tenth century to the early sixteenth century in the Latin West, as was the case with those reviewed in A survey of European astronomical tables in the late Middle Ages.2 Tables in Arabic and Greek are excluded, although many of the tables considered here have their origin in tables in those languages, or were simply adaptations of them into Latin. The period between the tenth and the sixteenth centuries is a consistent span of time for astronomical tables because all those concerning the movements and positions of the Sun and the Moon and the five known planets were ultimately based on the geometrical models described by Ptolemy (second century), thus allowing for few modifications.In this paper the main elements characterizing astronomical tables are defined and typologies of them are proposed according to their content and internal structure, as a contribution to their analysis, which has become a crucial way for understanding the computational methods and the transmission of astronomical knowledge.A THEMATIC CLASSIFICATIONAstronomical tables, in their huge variety, can be classified according to different criteria. From the point of view of their content, it is possible to group tables into several categories, each one with a variety of types. The categorization proposed here follows in many ways the patterns established by several modern authors who have surveyed specific sets of tables such as Islamic tables, the Toledan Tables (eleventh century), and others.3 The thematic classification below works very well even though in a few cases it has been difficult to assign to a single category certain tables that contain varied information. …