Kitāb al-jadwal al-mubārak fī ʻilm al-zamān wa-al-falak fī ḥisāb madākhil al-ashhūr al-ʻArabīyah wa-al-Rūmīyah

Because of the religious obligation to perform canonical prayers at set times of the day and the sanctity attributed to particular times of the year, such as the month of Ramaḍān, Muslim scientists have studied questions relating to the calendar and the reckoning of time almost since the beginning of Islam. The present manuscript presents tables for the comparison of the Hijrī and Christian years. Little is known of the author of these tables, al-Ḥusayn ibn Zayd ibn 'Alī ibn Jaḥḥāf, beyond a marginal note, which states that Ibn Jaḥḥāf was a famous astronomer under the caliphate of al-Ḥākim bi-ʼAmr Allāh, who ruled over Fatimid Egypt in 996-1021. The calendrical tables that constitute the main part of the work are preceded by an explanation of how to read the tables. In particular, the author notes his use of the Arabic alphabet according to a peculiar traditional arrangement known as abjad. The introductory essay touches upon the particular features of leap years as opposed to regular years and defines the concept of the solstice. The tables are followed by short scientific poems that deal with the times of sunrise and sunset and the description of the 28 lunar mansions. The manuscript was transcribed by Maḥrūs al-Ḥidyah in 1729. The text is Naskhī script, principally written in black ink with titles in red and green, and is framed by a double red line. The last folio of the manuscript seems to have been written at a later time, in a less neat handwriting, probably by the same person who added the biographical note on Ibn Jaḥḥāf at the opening of the work. The manuscript previously was owned by a scholar active in the first half of the 18th century, Muḥammad ʻAlī ibn Ẓāhir Watarī, and was later in the collection of Shaykh Maḥmūd al-Imām al-Manṣūrī, professor of religion at Al-Azhar University in Cairo, which was purchased by the Library of Congress in 1945. World Digital Library. The text is a popular exposition on the study of the order of events in time, and the order in which they occur, especially in those related to astronomical movements and the measurement of time. Note on fol. 2a in another hand says that the author was a famous astronomer during the reign of the Fatimid Caliph al-Ḥākim bi-ʼAmr Allāh (d. 411 AH/1021 AD). Fol. 1b and 12b contain instructions (in the same hand) on calculating dates in the past (pages missing after fol. 12b).