The author this commentary, Ṣalāh al-Din Musa ibn Muḥammad, also known as Qādī Zāda (the son of the judge), was born in Bursa (present-day Turkey) in 1364 and died in Samarkand (present-day Uzbekistan) in 1436. His first teacher, al-Fanāri, suggested that he move to the scientific centers of the time, Herat in Khorasan (present-day Afghanistan) or Bukhara or Samarkand in Transoxiana, in order to develop his extraordinary ability in the mathematical and astronomical sciences. Following this advice, Qāḍī Zāda presented himself to the Samarkand court of the very promising Ulugh Beg (1394–1449), who was just 17 years old at the time. Ulugh Beg became Qāḍī Zāda’s most talented pupil and assured him the funds for a life of study in Samarkand. Combining research in local facilities (including the famous Ulugh Beg Observatory built in the 1420s) with his educational activity, Qāḍī Zāda wrote a number of commentaries on works of mathematics and astronomy, including the one preserved in this manuscript. Most likely intended as a didactic work, this treatise is an extensive commentary on an astronomical textbook by Šaraf al-Dīn Mahmūd ibn Muhammad ibn ‘Umar al-Jaġmīnī, Mulahhas fī al-Hay'a Al-Basīta (The compendium of plain astronomy). Qāḍī Zāda's commentary, though widely expanding on the contents of the Mulahhas, tends to follow its structure, dealing with the configuration of the celestial and terrestrial worlds and the divisions of the created bodies, the celestial orbs, and the Earth. The manuscript is enriched by many marginal notes written in different hands, reflecting the high scientific and educational value attributed to Qāḍī Zāda's commentary after his death.