The aim of this paper is two-fold: first, after having given the main characteristics of the Portuguese cultural background at the end of the 14 th century and, dominantly, the context of the knowledge of astronomical matters in Portugal in the 15 th century, we give one example of how Portuguese navigations in the 15 th and 16 th centuries helped to change qualitatively the world-vision in the
... [Show full abstract] 16 th century. Then we show how the Portuguese navigators used Astronomy, set in the Aristotelean-Ptolemaic model of the world, to succeed in their navigations, in this way contributing to change the world-vision, and consequently also preparing the coming scientific revolution. In particular we discuss the Regulations concerning the Pole Star, the Sun, and the Southern Cross constelation.