AḤMAD B. MOḤAMMAD ṢĀḠĀNĪ, ABŪ ḤĀMED, one of the many astronomers who worked for the Buyids in Baghdad in the 4th/10th century. Thus Bīrūnī (Taḥdīd al-amāken, ed. P. Bulgakov, Cairo, 1964, p. 100; tr. J. Ali, Beirut, 1967, p. 69; commentary E. S. Kennedy, Beirut, 1973, p. 43; see also al-Qānūn al-masʿūdī, Hyderabad, 1954-56, p. 364) quotes from his lost Kētāb al-qawānīn his determination of the obliquity of the ecliptic and of the latitude of Baghdad in A. H. 374, Yazdeǰerdī 354 (20 March-23 May 985); Bīrūnī (al-Qānūn, pp. 659-60) also reports that he observed the lengths of the seasons at Baghdad in Yazdeǰerdī 355 (20 March 986-19 March 987) in order to determine the longitude of the solar apogee. According to Ebn al-Qefṭī (Taʾrīḵal-ḥokamāʾ, ed. J. Lippert, Leipzig, 1903, pp. 79, 353) and Abu’l-Faraǰ (Taʾrīḵ moḵtaṣar al-dowal, Beirut, 1958, p. 176), he was associated with Kūhī in the observatory established in that same city under Šaraf-al-dawla (r. 376-79/987-89). Apparently, he was responsible for the instruments in that observatory. Abu’l-Faraǰ adds that Ṣāḡānī died at Baghdad in 379/989-990; Ebn al-Qefṭī (TaʾrīkÂ², p. 79) narrows the time to Ḏu’l-qaʿda or Ḏu’l-ḥeǰǰa of that year (31 January-30 March 990). Bīrūnī provides additional information about Ṣāḡanī’s activities. He notes, for instance, his determination of the solar equation (Tamhīd al-mostaqarr fi’l-taḥqīq maʿna ’l-mamarr, in Rasāʾel al-Bīrūnī, Hyderabad, 1948, pp. 22-23; tr. M. Saffouri and A. Ifram, Beirut, 1959, p. 26), his development of a method of stereographic projection for use in astrolabes (see below, no. 1; Āṯār al-bāqīa, p. 357; Chronology, p. 357), and his report of the expedition sponsored by Maʾmūn to measure the circumference of the earth (Taḥdīd, ed. p. 214, tr. p. 179, commentary, p. 233). For this report he depended on Ṯābet b. Qorra. Seǰzī (Woepcke, L’Algèbre d’Omar Alkhayyāmī, Paris, 1851, pp. 119, 123) quotes two propositions concerning the trisection of an angle from him.
Ṣāḡānī’s surviving works are: 1. Ketāb fī kayfīya tasṭīḥ al-kora ʿalā saṭḥ al-asṭorlāb (“Book on the manner of projecting a sphere on the plane surface of an astrolabe”), published as item 7 in al-Rasāʾel al-motafarreqa fi’l-hayʾa, Hyderabad, 1948. 2. Resāla fi’l-sāʿāt al-maʿmūla ʿalā ṣafāʾeḥ al-asṭorlāb (“Epistle concerning the hour-lines constructed on the tympans of an astrolabe”). 3. Maqāla fi’l-abʿād wa’l-aǰrām (“Treatise on the distances and sizes [of certain celestial bodies]”). 4. Resāla fī ʿamal żeḷʿ al-mosabbaʿ al-motasāwī le ażlāʿ fi’l-dāʾera (“Epistle on constructing the side of an equilateral heptagon in a circle”).
See also A. Sayili, The Observatory in Islam, Ankara, 1960, pp. 110-15.
Sezgin, GAS V, p. 311.
Originally Published: December 15, 1984
Last Updated: July 28, 2011
This article is available in print.
Vol. I, Fasc. 6, p. 654
David Pingree, “AḤMAD ṢĀḠĀNĪ,” Encyclopædia Iranica, I/6, p. 654; an updated version is available online at http://www.iranicaonline.org/articles/ahmad-b-21 (accessed on 19 March 2014).