1. Historical Background

In the 13th century, Trebizond became the capital of a small independent state known as the Empire of Trebizond under the rule of the Grand Komnenoi dynasty. Despite its relatively small population,¹ the city became a powerful commercial entrepot thanks to its position along the route of caravans connecting the East with Constantinople and the West through Persia of the Il-Khanid Dynasty. This very geographical position also favoured the direct contact with the scientific debate on astronomy, held in Persia in the same period, mainly in the cities of Tabriz, and Maraga (Marāgheh-Marāghah), where new observatories had been founded.²

2. Introduction of Persian Astronomy

In the 13th century, the Mongol descendants of the dynasty of Genghis Khan established two of the most important observatories in the history of the Islamic astronomy, one in Maraga³ (1259) and another one in Tabriz (late 13th century). According to the Arabic tradition, as the latter had been formed in Baghdad, the astronomers in Persia attempted to re-examine the principles of astronomy, as they had been introduced and established by Claudius Ptolemy and had been followed by the Byzantines until then. This effort led to a new way of establishing astronomical rules, which was entered in the Zij, the Persian astronomical textbooks, which probably were named after their tables that resembled meshes of tense strings (Zij: string).⁴

The new developments of the Persian astronomers were introduced to Trebizond by Gregory Chioniades, who was actually the founder of the noteworthy astronomical school established in Trebizond. Chioniades visited Tabriz and attended the classes of Shamsh al‑Din al‑Bukhari, whom he mentions as Shamsh Pukharis.⁵ Then the scholar brought back to Trebizond Persian manuscripts and the handwritten notes he had taken in the classes of Bukhari, as well as the tables of his works. These texts were found in the hands of the monk Manuel, who was a teacher of astronomy in Trebizond in the early 14th century.

3. New Characteristics

When Chioniades introduced the texts from the observatory of Tabriz, it was a period when the Byzantine circle of scholars had begun to face some problems with the old Ptolemaic measurements, which resulted in problems with the astronomical calculations and the construction of tables; the problems were only to become bigger in the course of time. The fact that Nikephoros Gregoras, in 1332, suggested the reformation of the existing calendar as a possible solution to the problem, is quite eloquent. The new Persian calculations seemed to actually provide more accurate positions of the planets, the sun and the moon, thus leading to more accurate calendar calculations and prediction of the eclipses.

Manuel started to teach astronomy based on the works of the Persian astronomers Shamsh Bukhari and Nașīr al-Dīn al-Tūsī, that is, according to the new calculations carried out by those who belonged to the groups of the observatories of Maraga and Tabriz. Following the Ptolemaic method, this new approache takes into account the conclusions and measurements resulting from observation, thus changing the principles followed until then in calculations, while they introduced new evidence on the movement of planets, as this evidence results from observation.

The classes given by Manuel must have become well-known outside the territory of the small state in Pontus. Manuel wrote astronomical and astrological discourses⁶ (he is also considered to be the author of the ‘Almanac of Trebizond for the year 1336’). It should be noted that the new methods of calculation introduced from the Persian-Islamic astronomy are much easier in use than the respective Ptolemaic method. As a result, the positions of the celestial bodies, the syzygies and the eclipses, that is, anything used for the preparation of astrological and astronomical tables as well as for the estimation of the exact date of Easter, could be now calculated more easily. This fact helped both the diffusion of the new methods in Trebizond and their being accepted by a large number of scholars in Constantinople.

George Chrysokokkes travelled to Trebizond to acquire this knowledge and in 1347 he wrote the work ‘Introduction to the Syntaxis of the Persians’, as it is known, or ‘Introduction to the Syntaxis of the Persians to His Brother Ioannes Charsianites’, as its complete title is. This work introduced and spread the Persian astronomy all over the Byzantine Empire and the scientific circles of Constantinople, from where it was also spread to the West.

4. Evaluation

Astronomy as it was developed in Trebizond resulted from the convergence of the Ptolemaic and the Persian tradition. The new methods of calculation introduced from Persia were more convenient, although they were not always reliable, probably due to errors during their transferral. They renewed the interest in astronomy and promoted further developments by creating a new school in Trebizond, Constantinople and the western Europe.