Timurid and Arabian contributions
During the first half of the 15th century, Timur's grandson, Ulugh Beg, ruled over the Mongol empire his ancestors had built from Genghis Khan on. Main scientific figure of this "Timurid Renaissance" who illustrated the famous saying "there is no document of civilization which is not at the same time a document of barbarism" [1], Ulugh Beg built one of the most famous astronomical observatories of all time in Samarkand (now in Uzbekistan), from 1424 to 1429. He himself led the about seventy researchers who gathered the Zīj-i Sultānī (Persian : زیجِ سلطانی), the most ambitious star catalog since Ptolemy, where the coordinates of more than one thousand stars and planets were determined, as well as Saturn rotation cycle, methods of calculation to predict eclipses, and extremely precise measures, including measures of the sidereal year and of the obliquity of the ecliptic.
Delisle's interest in Ulugh Beg's Zīj could stem from his familiarity with the work of Hevelius, whose Prodromus Astronomiae frontispiece shows the Timurid prince in the company of major figures like Ptolemy and Tycho Brahe :
from the left to the right, Hevlius, the landgrave of Hesse, Ulugh Beg, Ptolemy, Tycho Brahe and Riccioli sitting next to the muse Urania (in the center)
a page of the Zīj-i Sultānī, translated by "Georgius Jacobus Kehr, Saxo, Philosophiae Doctor"
Some of Delisle's colleagues in Saint Petersburg had a sound knowledge of the Persian language : the Georgian tsar Vakhtang VI, his two sons Bakar and Vakhouchta, as well as the orientalist Georg Jacob Kehr. [2] Delisle's collection includes a portfolio of "Ulugh Beg's astronomical tables in Persan with a translation" by the latter. This beautiful ensemble (whose latin translation is only partial) consists of tables "of the Sun and the Primum Mobile", of the Moon, Mercury, Venus, Mars and Jupiter, among other things. [3]
the table of contents
Written in Persian, Timurid astronomy fully belongs to the Arabic tradition. It was an occasion for Delisle to consider it. During the session of Saint Petersburg Academy when he read the Zīj's preface and gave his own study "on a Persian manuscript of Ulūgh Beg's astronomical tables", according to Nina I. Nevskaja, Delisle gave a "detailled presentation of Naṣīr al-Din al-Ṭūsī, Ibn Yūnis, al-Farabi, Ulūgh Beg and other authors' scientifical legacy". [4]
in this addition to his abrégé de l'histoire des observations astronomiques, Delisle asserts he has "been aware of the observations of the Arabs, the Persians and other Easterners reported in ibn Yunis' ms" from Leyde's library
We will only consider here the name of Ibn Yūnus (sometimes Yūnis). He "flourished", as Delisle wrote, "a little before the year 1000 A.D." [5], i.e. in the 380s and 390s of the Hegira. In Cairo, he published a remarkable treaty, which was a comprehensive survey of the observations of the two previous centuries. It was entitled the Hakemit Tables (al-Zij al-Kabir al-Hakimi), after the Fatimid Caliph Al-Hakim.
The historian Régis Morelon points out that "the precision of this astronomer's observations, since his results were made available by a translation in the beginning of the 19th century, was used by modern scientists, for instance, to get a better knowledge of the moon's secular acceleration." [6] Delisle kept several records of lunar and solar eclipses. His collections also include an anonymous note about the location of the Egyptian astronomer's observatory. [7]
a page from Caussin de Perceval's translation of the Hakemit Tables (1804)
[1] Walter Benjamin, VIIth of the Theses on the Philosophy of History, in Illuminations, trans. Harry Zohn, ed. Hannah Arendt, New York: Schocken, 1969, p. 256.
[2] Nina I. Nevskaja, op. cit., p. 312.
[3] Delisle collection, portfolio B5/17.
[4] Nina I. Nevskaja, ibid. It is the session of 25th June 1739.
[5] Delisle collection, portfolio A7/10, piece 53.
[6] Régis Morelon, "L’astronomie orientale (VIIIe-XIe s.)", in Roshdi Rashed (dir.), Histoire des sciences arabes, vo. 1, Astronomie, théorique et appliquée, Paris : Seuil, 1997, p. 66.
[7] Delisle collection, portfolio A1/11, piece 61.