Two major works on twilight
Pedro Nunes & Ibn Mu'adh, 1542
NUNES, Pedro (1502-1578) and IBN MU'ADH, Abu 'Abd Allah Muhammad (989-1079). De crepusculis liber unus, nunc recens & natus et editus. Item Allacen Arabis vetustissimi, De causis crepusculorum liber unus. Latter text translated by Gerard of Cremona. [Lisbon: Luis Rodriguez, 1542.]

First edition of two major works on twilight. The first is by Pedro Nunez, the great Portuguese mathematician who served as royal cosmographer at the court of João III. It contains a new solution to the problem of shortest twilight and the design for an astronomical instrument called the "nonius" for taking finer angular measurements. The second text, printed under the same title, is a translation of a work once attributed to Ibn al-Haytham, but now thought to be by the great Andalusian father of spherical trigonometry Abu 'Abd Allah Muhammad ibn Mu'adh. It is “a short work containing an estimation of the angle of depression of the sun at the beginning of the morning twilight and at the end of the evening twilight, and an attempt to calculate on the basis of this and other data the height of the atmospheric moisture responsible for the refraction of the sun's rays” (Sabra). Anselmo 300; see A.I. Sabra, "The Authorship of the Liber de crepusculis" in Isis, vol. 58.1, Spring 1967.

Quarto (197 x 150mm). Woodcut border on title, woodcut printer’s device on final leaf, woodcut diagrams and initials (neatly repaired tear to final leaf, very light occasional soiling). Old gilt paneled calf with author’s name stamped in central device (lightly rubbed at extremities). Provenance: early ownership inscription trimmed at top edge of title – Bibliothèque publique de Douai (stamps on title, including release).