Meridian Determination Methods in Masudic Canon and Indian Circle

Abstract

Ebu’l Reyhân Muhammed bin Ahmed al-Birûnî is one of the most important mathematics
and astronomy scholars of the 11th century. In his book al-Qānūnu’l Masʿūdī
fiʾal-Hayʾa waʾl-Nucūm, he describes theoretical astronomy subjects, astronomy tables
and astrological methods of his period. This paper aims to examine the meridian line
(nisfunʾnehâr) determination methods in al-Qānūnuʾl Masʿūdī and the section where the
Indian Circle is explained. In the article, the section in question was translated into Turkish
by creating a critical text, the principles of the method were analyzed and its mathematical
interpretation was fulfilled. E. S. Kennedy has a short study on only the last of the methods
described by Bīrūnī. In our study, all the methods that Bīrūnī analyzed are explained. In
the first part of the two-part article, a tracing attempt of the Indian circle was made. Indian
Circle is not seen in Ptolemy’s studies. The historical development of it in the Siddhantas
and in the content of the zîjs and (hayʾa) theoretical astronomy works of the Islamic World,
were examined. In this tracing attempt, the possibility of Bîrûnî being the person who
introduced the concept of the Indian Circle to the literature was questioned. Depending
on this conceptualization effort, Bîrûnî’s didactic method in his works and his meticulous
effort in conceptualization are revealed by focusing on the issue of meridian determination
and by giving examples from his other books. In the second part, the translation of methods
regarding determining the meridian line and the updated drawings of the figures were
interpreted. In the article, different manuscripts of al-Qānūnu’l Masʿūdī were examined
and a new drawing of the described geometric model was made according to the latitude
of Istanbul. The drawings in question were created by comparing different manuscripts of
the work, based on the copies of Oxford Bodleian 516, Velüyüddin 2277. The translation
and critical text were made by comparing the printed Hyderabad edition of the book, Oxford
Bodleian 516, Veliyüddün 2277, Berlin 1613, and Kandilli 364 manuscript versions.