The beginning of celestial navigation

The use of the observed positions of celestial bodies to determine the location of a navigator and to direct vessels, was an aspiration of ancient seafarers. Various peoples, in the Mediterranean as much as in the Indian Ocean, in China as much as in the Pacific, looked up to the sky as a guide for ships, but there is no convincing evidence this was achieved until the Modern Age. It was not before the Modern Age that two techniques were developed by the Portuguese, the measurement of the altitude of the North Star and that of the meridian altitude of the Sun, which, adapted and simplified for the use of sailors, enabled them to achieve good accuracy at least as far as the measurement of latitude was concerned. To this end, instruments that had already been used by astronomers for several centuries were also adapted and simplified: the quadrant, the astrolabe and, later, the cross-staff.