Kitāb qurrat al-ʻayn fī tasyīr al-nayyirayn

Little is known about the astronomer Muḥammad ibn ʻAbd al-Qādir al-Khalīlī al-Jaʻbarī, who wrote the treatise Kitāb qurrat al-'ayn and prepared the accompanying astronomical tables preserved in this copy. Some information about the original work can be inferred from information provided on the last page of this manuscript, where the colophon specifies that the copy was produced in the year 932 AH (1525), based on an older, quite damaged manuscript. This information gives us a terminus ante quem (latest possible date) for the original work. The treatise also opens with an introduction, in which the author explicitly acknowledges his intellectual debt to the astrological works of Ibn al-Shāṭir, a famous inventor of a planetary model that harmonized medieval theory with direct observation, thereby improving the effectiveness of the Ptolemaic system. Ibn al-Shāṭir is known to have died in 1375. The original work by Muḥammad ibn ʻAbd al-Qādir al-Khalīlī al-Jaʻbarī thus must date from between the late 14th century and the early 16th century. The first part of the introduction extends over just three pages and touches upon various problems of calendrical reckoning: the correct identification of days of the month according to the Islamic, Byzantine, and Coptic year; how to differentiate between the Byzantine and Coptic calendars; and how to calculate a date in each of these systems. The second part of the introduction begins at folio 4 verso and is devoted to astronomical problems, in particular the movements of the sun and the moon in the sky. The collection of tables that occupies the second and larger section of this manuscript follows the outline of contents explained in the introduction. The first tables are devoted to calendrical problems and equivalences between different dating systems, while the second set of tables deals with measurements of the movements of the sun and the moon. While the astrological tables are outlined with red ink and show a noticeable care in their layout, the introduction is written in a rather slapdash hand that could indicate a private destination for this copy. World Digital Library. The text is principally based on the writings of ʻAlī ibn Ibrāhīm Ibn al-Shāṭir (1304-1375), as the introduction mentions. The colophon says that the text was copied from a manuscript with many errors written in a bad hand.