The Stars and Navigation
The astronomical methods used to determine the position of ships at sea required maps in geographic coordinates
Astrology and astronomy played a leading role in the evolution of nautical sciences. In view of its development, combined with mathematics and geometry, the true shape of the continents became known and the mastery of the skies and stars grew.
This increase in knowledge constituted one of the greatest Portuguese contributions to humanity’s progress and opened the paths to European relations, helping their culture spread around the globe.
The astronomical methods used to determine the position of ships at sea required maps in geographic coordinates, where bathymetry and the position of coasts and islands were referenced by rigorous methods.
It became necessary, then, to study a way to discover the location of ships at sea without resorting to known coasts. For this, the stars became mechanisms for deciphering geographical positions.
During the day, the Sun acted as the main orienteering star, being necessary to regulate the hours between the hourly determinations, the use of sand hourglasses with a duration of thirty minutes that were regularly turned throughout the day.
On board Portuguese ships in the 16th century, hourglasses were set at noon, when the meridian height of the Sun was determined.
Chronographia o Reportorio de tiempos el mas copioso y precisso q. hasta ahora ha salido a luz, pág. 201 (1584) by Jeronimo de ChavesBiblioteca Central de Marinha
In addition to the sun, other smaller stars and the moon itself represent a way of discovering coordinates. The measurement of hours is based on the apparent annual movement of the line joining the Polar and the Front Guardar.
It is possible, through the nocturlabe, to measure the angular variation of this line between the time when the night began and the time when the time is being determined.
Regimento de pilotos e roteiro das navegaçoens da India Oriental. agora novamente emendado & acressentado com o Roteiro da costa de Sofala ate Mombaça & com os portos & barras do Cabo de Finisterra ate o estreito de Gibaltar(…) , estampa 5 (1642) by António de Mariz CarneiroBiblioteca Central de Marinha
The application of advances in nautical astronomy, oceanography and cartography resulted in the development of charts and, consequently, atlases.
Theatrum orbis terrarum (1584) by Abraham OrteliusBiblioteca Central de Marinha
The atlases combine geographic rigor and precision in the representation of the coasts and the beauty of the illumination.
Theatrum orbis terrarum (1584) by Abraham OrteliusBiblioteca Central de Marinha
Theatrum orbis terrarum (1584) by Abraham OrteliusBiblioteca Central de Marinha
