Introduction To Astronomy By Theodore Metochites: Stoicheiosis Astronomike 1.5-30

(Stoicheiosis Astronomike 1.5-30)

Emmanuel Paschos, Christos Simelidis;;;

• Publisher: WSPC
• Year: 2017
• eBook ISBN: 9789813207509
• Topic: Physical Sciences
• Subtopic: Science History

-->

Stoicheiosis Astronomike ("Elements of Astronomy") is a late Byzantine comprehensive introduction to Astronomy. It was written by an outstanding figure in Byzantine culture and politics, who served also as prime minister. This volume makes available for the first time a large part of its astronomical contents, offering the original text with an English translation, accompanied by an introduction and analysis.

This book describes the celestial spheres, the rotation of the planets, and especially the apparent trajectory of the sun with its uniform and anomalous rotations, which are used to determine the length of the year. Metochites proposed a new starting date for the calendar (6th of October 1283) specifying the position of the sun on that date. The work revived the interest in studies of Ptolemaic astronomy as attested by numerous annotations in the margins of the manuscripts.

Besides its astronomical content there are statements on the epistemological method and other issues elucidating the spirit of that age. It will be of interest as an introduction to Byzantine astronomy for historians of science and philosophy, for astronomers, and those interested in the development of calendars.

-->

1. Introduction

The Stoicheiosis Astronomike is an extensive treatise on astronomy from the late Byzantine period. It was written by Theodore Metochites (1270–1332), who was a distinguished politician serving in high positions (1305–1328), including the highest posts of Grand Logothete (Chancellor) and mesazon or prime minister, under the emperor Andronikos II Palaiologos. During his illustrious career as statesman and scholar, he produced, besides the treatise on astronomy, literary and scholarly works including commentaries on Aristotle, hexameter poems, orations and hagiographical encomia.¹ He donated part of his wealth for the restoration and redecoration of the church in the Chora Monastery, where his portrait survives in a mosaic of the narthex. He enriched the library of the monastery and bequeathed it to his student Nikephoros Gregoras.² In 1313, at the advanced age of 43, he studied astronomy under Manuel Bryennios and wrote his Introduction to Astronomy, which is the subject of this book.

Metochites’ astronomical treatise expounds upon the movements of celestial bodies as they were understood in the late 13^th and early 14^th century. The text covers most topics related to the solar system: the Sun, the Moon and the five planets. It was written at a time in which Byzantium was experiencing a revival of interest in classical studies, especially mathematics and astronomy (Palaiologan Revival). This was a difficult time for Byzantium, when the finances and the dominion of the Empire were decreasing. In spite of these difficulties, there was flourishing astronomical activity as represented by the many surviving texts. The surviving astronomical texts fall into two categories. The first follows the ancient astronomical tradition: the texts and tables include results from ancient Greek and Hellenistic astronomy, presenting and elucidating astronomical results and then applying them to contemporary problems. The second group brought to Byzantium elements from Persian and Arabic astronomy and is more original. Metochites’ Stoicheiosis Astronomike follows the former school without recourse to direct observations. Metochites’ aim was partly educational and he succeeded in reviving the study of ancient astronomy in Palaiologan Byzantium. According to Pingree, Stoicheiosis “raised the level of sophistication in Byzantine astronomy to a height it had not attained for centuries”.³

In his effort to revive the interest in classical Greek knowledge, Metochites includes five introductory chapters covering ancient Philosophy, Mathematics and Astronomy. These chapters have already been studied and edited by Börje Bydén.⁴ Chapter one contains a narrative of how Metochites became involved with the project. The emperor Andronikos II was a cultivated man and asked him to undertake the project in order to improve the level of education and understanding. Metochites searched for a tutor and found Manuel Bryennios with whom he completed his studies.⁵ Bryennios had been taught by a man educated in Persia⁶ and thus one may suspect a connection with Persian astronomy. However, in Stoicheiosis, especially the text we analysed there is no evidence for such a connection. There is historical evidence that Gregory Chioniades visited Persia and brought back texts which he translated into Greek. Some scholars have discussed the interaction between the two schools of astronomy mentioned above and the transmission of knowledge, especially from the Maragha School.⁷ This transmission is absent in Stoicheiosis, but it appears in other works of Chioniades and Theodore Melitiniotes.⁸

The educational aim of Stoicheiosis is evident in many respects. At the very beginning of chapter five it is stated that “in this treatise we set out to present an elementary account of spherical astronomy”. Many topics are explained in detail and in the middle of such discussions are interjected comments of philosophical or epistemological nature. For example, in chapters six and seven Metochites describes the revolutions of the two higher spheres (the diurnal rotation and the precession of the equinoxes) in greater detail than in the Almagest 1.8. Establishing the precession was a difficult problem and Ptolemy presents in a later chapter (Alm. 7.2-3) extensive data to support it. Metochites’ description is very clear and he mentions that it is difficult to observe it. This gives him the opportunity to discuss the scientific method that one must follow in order to establish small effects by quoting the Harmonics of Ptolemy and Aristotle (7.59-77). This approach is found throughout the Stoicheiosis. The educational purpose is also revealed by concluding sentences like: “we elucidated with sufficient clarity the time difference between meridians” (27.96-97) or “the tables for the uniform and anomalous motion of the Sun … are constructed in this manner. They are well understood and have been presented in a way I consider useful” (25.1-4). Then he mentions explicitly the sources for the tables and includes instructions and examples on how to use them.

In Byzantium, Astronomy was part of the quadrivium and was taught in combination with mathematics.⁹ Our edition and study demonstrates the influence of mathematics on astronomy as well as Metochites’ level of mastering the subject and the issues discussed and investigated at that time by himself, his students and perhaps a small part of the public. There are precise physical and geometric statements, as well as numerical tables covered in his book. Finally, the text of the Stoicheiosis has a special style. At the beginning of many chapters Metochites includes a brief summary of the previous chapter. In many places the sentences are long and repetitive making the translation difficult. We tried to make the reading of the translation easier by limiting repetitions in order to present the content of sentences and of entire paragraph(s).

Medieval treatises on scientific topics are frequently difficult to appreciate, and sometimes misunderstood, because at that time the concepts, notation and terminology were very different from those we use today. The task of appreciating them becomes even more difficult when their author is not a professional scientist but rather a newcomer, an amateur or, as in our case, a high state official who presents his arguments in a scholastic manner. For these reasons it is necessary for studies of these works to analyse their contents (descriptive and mathematical) in order to see the connection with the past and the influence they exerted in the future. The complete understanding of Metochites’ work requires a critical edition of the Greek text, as well as a translation and exposition of its contents. B. Bydén’s analysis of the first five chapters of the treatise is based on an impressive knowledge of the reception of ancient philosophy in Byzantium. However, the bulk of the treatise, which contains the astronomical part of the work, remains unpublished. In this book we start with the 5^th chapter of Stoicheiosis, which outlines the purpose of the treatise. We include all chapters up to the 30^th, an extensive section of the treatise which is self-contained. It covers the revolutions of the upper three spheres: the diurnal rotation, the precession of the equinoxes and the apparent rotation of the Sun on the inclined (ecliptic). Our work stops at the place where the study of the Moon begins. There are several other topics covered in these chapters, such as the Egyptian, Greek and Roman calendars leading to a proposal for changing the initial date for measuring time. It describes the correlation of times among the various geographic zones (ascensions), the obliquity, and contains extensive tables with instructions on how to use them. The format of our study, which offers a textual introduction, text, translation and analysis, makes available for the first time the astronomical content of chapters 6-30.

Metochites’ work prepared the ground for further work and we mention a few of the recorded developments. A recurring topic those days were methods for measuring time and the accuracy of the Julian calendar. The interest in these topics is related to the determination of the day for the celebration of Easter (Paschalion). An early proposal for revising the calendar appears in chapters 25 and 26 of Stoicheiosis. Metochites proposes a new beginning for the calendar coinciding with the first year of the reign of Andronikos II. In these chapters he determines the day of the year for the new beginning and the position of the Sun on that day. The chapters attracted attention, as indicated by many marginal notes, with the most extensive written by John Chortasmenos (ca. 1370–ca.1436/7). Many copies of the Stoicheiosis also contain annotations by Nikephoros Gregoras (1295–1358), who was a pupil of Metochites and became an accomplished astronomer himself. Notable among his contributions is the description of a plan to correct the calculation for the length of the year and thus determine the date for celebrating Easter. In the Roman History he mentions the revision, but does not include details or numerical values.¹⁰ In the surviving manuscripts it is stated that the length of the tropical year estimated by Ptolemy must be corrected. Nine years later Barlaam of Calabria (ca. 1290–1348) revisits the determination of the date of Easter.¹¹ For the spring equinox he follows the method and values from the Megiste Syntaxis (Almagest) and then he diverts the discussion to the prediction of full Moons. Much later, Isaac Argyros (ca. 1300–ca. 1375), a student of Gregoras, commenting on Gregoras’ discovery states that “the correction required is obtained by subtracting 1/200 of a day from the Ptolemaic figure or about 1/100 of a day from 365 and one-quarter days.”¹² This value is very accurate for the length of the tropical year (Argyrus’ value of 365.2417 days is close to the present value of 365.2422 days).

Needless to say, that none of the proposals was adopted, because of varying opinions among astronomers and because of the political events that followed. Andronikos II was deposed in 1328 and Gregoras’ political and religious views fell into disfavour to the extent that he was imprisoned. The short narrative shows that many astronomers were indebted to the works of Metochites. The Stoicheiosis was studied for quite some time, and John Chortasmenos notes, two generations later, that with the Stoicheiosis it was then possible to navigate across the sea of Ptolemy’s thought.¹³

The detailed presentation of the text, including the numerous tables with instructions on how to use them and the exposition of intricate concepts support the view that Metochites contributed to the revival of astronomy along the lines of the classical Greek tradition. There are changes on various topics and we elaborate on two of them. As mentioned already, in chapters 25 and 26 there is a proposal for selecting a new date for measuring time by determining the date of the year and the position of the Sun on that date. The proposal attracted a lot of attention for a few generations as indicated by the commentaries on the margins. The second change has to do with the catalogues for the positions in longitude of the fixed stars of first and second magnitude. Metochites explains at length that the positions change due to the slow precession of the equinoxes at a rate of one degree in one hundred years. We studied the tables in the manuscripts and found the following. In Vat. gr. 182 (V), ff. 249v-250r, the values for the longitudes advanced by approximately 11° from the values of Ptolemy. In Vat. gr. 1365 (C), ff. 241v-242r, the values for the positions of the stars are the same with those given in the Megiste Syntaxis. Bydén has given serious arguments, which were confirmed by our study, that V precedes C and was closer to the original text of Metochites. Once we accept this chronological sequence the earlier document includes the correction from the precession of one degree in one hundred years. For unknown reasons the scribe of C decided to return to the values of Megiste Syntaxis.¹⁴ In Vat. Gr. 1087 (G) the scribes (which included Gregoras) have only partially completed some of the tables, with the tables of the fixed stars being empty.

Inconsistencies among tables are also present in the various manuscripts of the “Tables of fixed stars in the Persian Syntaxis of George Chrysokokkes”, compiled and discussed by Kunitzsch.¹⁵ In this work the tables of type-III are closest to the tables of the Stoicheiosis. In table of type III, the values in the various manuscripts are very different, varying from Ptolemy’s values +11° 55΄ up to Ptolemy’s +19° 30΄. Regarding the tables there is a recurring pattern of discrepancies that has not been clarified yet. One possibility may be that since the tables were used for the determination of Easter, some scribes for religious reasons decided to return to the values of Ptolemy. In our case, the scribe of G was perhaps planning to correct and complete the tables at an opportune time but he never came to complete this task.

A curious aspect in Stoicheiosis is that Metochites gives instructions on how to calculate the position of the Sun and of the stars and gives answers without including numerical calculations. This is most evident in chapters 25 and 26 for the position of the Sun on the sixth of October 1283. The numerical work was added by John Chortasmenos in the margins (scholia). Metochites gives the impression that he provides the theory and expects others, perhaps his assistants, to complete the calculations which were carried out only in a few cases.

Among the topics covered in the book are t...

Table of contents

• Cover page
• Title page
• Copyright
• Preface
• Table of Contents
• 1. Introduction
• 2. Table of Contents of Stoicheiosis Astronomike
• 3. Textual Introduction
• 4. Sigla and Abbreviations
• 5. Stoicheiosis Astronomike 1. 5-30: Text & Translation
• 6. Analysis
• Bibliography
• Index