Astronomical navigation by solar altitude (Portugal)
Navegación astronómica por la altura del Sol (Portugal)
- Date
- c. 1480-1500 · confidence low
- Place
- Lisbon, Portugal
- Credited to
- Cosmographers of John II (José Vizinho, Abraham Zacuto) and Portuguese pilots
- Field
- Movement
⚠️ Disputed: the sources disagree.
What it is
A method for finding latitude on the open sea by measuring the Sun's altitude at noon with an astrolabe or quadrant and correcting it with solar declination tables, once the Pole Star is no longer visible south of the equator. It replaced dead reckoning as the basis of oceanic navigation.
The date, the existence of a “Junta dos Matemáticos” around 1484 and the specific authors are debated: the sources are late (Barros, 16th century) and the mariner's astrolabe is only documented with an image in 1517. It is accepted that Portuguese pilots were measuring latitude by the Sun from the 1480s.
What it led to
- navigation manuals (Regimento do astrolábio e do quadrante)
- latitude as a reliable coordinate on overseas voyages
- pilot training at the Casa da Índia and the Casa de la Contratación