Mozaffari, S. Mohammad (Author)
Journal of Astronomical History and Heritage
Volume: 26
Issue: 2
Pages: 469-488
The observational legacy of Abu ʾl-Wafāʾ al-Būzjānī, one of the tenth-century Islamic precursors in forming and developing trigonometry and spherical astronomy in the same form as we know today, is investigated in this paper. The relevant data have been, partly, presented in his Majisṭī and, partly, preserved by his younger contemporary and correspondent, Abū al-Rayḥan al-Bīrūnī. Of five surviving stellar observations, his ecliptical or polar longitudes for Capella, Deneb, Mizar, and Regulus are accurate to within –, but there is an error of –½° in the case of Altair. It is shown that his value of 1°/75y for the rate of precession is the result of his comparison of his own value for the longitude of Capella in the 970s with the corresponding value that can be considered as the star’s longitude in the Almagest for Timocharis’ time. He established an accurate solar theory on the basis of a series of observations made about the equinoxes and Summer solstice in 974 C.E. as well as at mid-Winter, mid-Spring and mid-Summer in 976 C.E. His times of the first three events were accurate to within – hours, and the errors in the successive intervals of time between the last three events amounted to +1½ hours. As a result of this remarkable degree of accuracy, the errors in the longitude of the Sun never exceeded the narrow range of –1′ to +4′ at the time. A systematic negative error is detected in the solar noon-altitudes with a mean of about –5′, which, in combination with a positive error of the same size in the meridian altitude of Capella, supports the hypothesis that either there was a northward tilt in the set-up of his meridional ring, or the observing site had a northward slope.
...MoreArticle Shi Yunli (2023) Introduction. Journal of Astronomical History and Heritage (pp. 281-281).
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