The present manuscript is a commentary entitled Anwār al-nujūm (The lights of the stars) by an author who appears to have stated his name as Jamist al-Rumi (Jamist the Byzantinian). The work is based on Al-zīj al-jadīd (The new astronomical tabulations) by Alī ibn Ibrāhīm Ibn al-Shāṭir (died 1375), the most-distinguished Muslim astronomer of the 14th century. Ibn al-Shāṭir was active as muwaqqit (timekeeper) at the Umayyad mosque in Damascus, where he constructed a magnificent sundial to adorn the central minaret; it had special curves to measure the times for the five daily prayers. The extensive treatise on which this commentary is based is called “the new astronomical tabulations” to distinguish it from a previous, and now lost, work also by Ibn al-Shāṭir simply called Zīj (Astronomical tabulations). Ibn al-Shāṭir's research for the first Zīj allowed him to develop revolutionary ideas regarding planetary astronomy. He departed from the traditional Ptolemaic astronomical model for a system that preserved and even enhanced the correspondence between foreshadowed and observed phenomena. He changed Ptolemy’s system whenever it implied non-uniform motions of the planets—uniformity being one of the Aristotelian attributes for the motion of celestial matter. The results of this substitution are of interest for several reasons. While creating a model that was mathematically consistent with the Ptolemaic one, Ibn al-Shāṭir was able to formulate a planetary theory of circular uniform motion, in compliance with Aristotelian ideas on matter. The main text, which extends for almost 300 folios, is surrounded in many places by marginal notes that appear to be in the same hand as the main text. These marginalia not only comment on the text itself, but provide extensive calculations and other information derived from Ibn al-Shāṭir’s treatise. The last 100 folios of the manuscript consist of astronomical tables, including tables for the conversion of different dating systems (Coptic, Persian, Byzantine, and Islamic). Jamist al-Rumi also provides times of sunrise and sunset during the year and all the practical information needed to perform timekeeping in Islam. A note on folio 1 rectoshows the name of ‘Abdallāh Musā ibn Muḥammad as the former owner of the codex, while a plate on the same folio mentions that that the manuscript later belonged to the East Asia Economic Research Bureau of the South Manchuria Railway Company, a Japanese company whose prominent red stamps can be seen the on first folios (1 rectoand 2 recto).