The sixteenth-century Yemeni navigator Sulaymān al-Mahrī is one of the two main Arab authors writing on maritime navigation in the Indian Ocean in the early modern and pre-modern periods. While he is generally known to have written five treatises on various aspects of the navigational sciences, he is also in fact the author of a sixth work, entitled Mirʾāt al-salāk li-kurāt al-aflāk (Mirror of Travellers into the Heavenly Spheres). Unlike his other works, Mirʾāt al-salāk is an introduction to astronomical concepts and practices that has previously been largely ignored by scholars on the subject. This article provides an introductory discussion of this text, situating it within its broader literary context, both within previous astronomical literature as well as the corpus of al-Mahrī’s other navigational works. It presents the ninth chapter of the work in particular in order to explore al-Mahrī’s familiarity with historical mathematical astronomical practices. Collectively, the work is an interesting textual example of the connection between navigational and mathematical astronomical knowledge.