Editing History of Portugal (1415–1578) (section)

==== Celestial navigation ====
[[File:AlmanachPerpetuum.jpg|thumb|right|200px|[[Ephemeris]] by [[Abraham Zacuto]] in Almanach Perpetuum, 1496]]
In the thirteenth century [[celestial navigation]] was already known, guided by the sun position. For celestial navigation the Portuguese, like other Europeans, used [[Arab]] navigation tools, like the [[astrolabe]] and [[Quadrant (instrument)|quadrant]], which they made easier and simpler. They also created the [[cross-staff]], or ''cane of Jacob'', for measuring at sea the height of the sun and other stars. The [[Southern Cross]] become a reference upon arrival at the Southern hemisphere by [[João de Santarém]] and [[Pedro Escobar]] in 1471, starting the celestial navigation on this constellation. But the results varied throughout the year, which required corrections.

To this the Portuguese used the astronomical tables ([[Ephemeris]]), precious tools for oceanic navigation, which have experienced a remarkable diffusion in the fifteenth century. These tables revolutionized navigation, allowing to calculate [[latitude]]. The tables of the Almanach Perpetuum, by astronomer [[Abraham Zacuto]], published in [[Leiria]] in 1496, were used along with its improved astrolabe, by [[Vasco da Gama]] and [[Pedro Álvares Cabral]].