Mariner's Astrolabe

Timeline

1. 1480–1500Lisbon and the Portuguese coast · Iberian PeninsulaPortuguese navigators and cartographers simplified the complex planar astrolabe into a lightweight brass ring disc, removing unnecessary dials and retaining only the sighting vane and degree ring needed to measure the altitude of celestial bodies, creating a practical mariner's astrolabe that could be hung aboard ship and withstand the rolling of the waves; they also compiled tables of the sun's declination to facilitate latitude conversion.
2. c. 1497–1600Atlantic and Indian Ocean routes · Indian OceanWhen Vasco da Gama rounded the Cape of Good Hope on his voyage to India in 1497, he carried a mariner's astrolabe to determine latitude; thereafter the instrument spread with Portuguese and Spanish expeditions throughout the Atlantic, Indian, and Pacific routes, becoming standard navigational equipment on European ocean-going sailing ships, with manufacturers in various countries imitating it and quality and precision continually improving.
3. 1621–1630Atlantic and Asian routes · PacificBetween 1621 and 1630, the mariner's astrolabe was still standard navigational equipment aboard the Dutch East India Company (VOC), the English East India Company, and Spanish galleon routes; together with the cross-staff and the compass, it formed the basic toolset for ocean navigation, and captains and pilots regularly used it to observe the noon sun's altitude to determine latitude.
4. 1730–1800European maritime nations · EuropeIn the 1730s the reflecting octant (Hadley's octant) appeared, far surpassing the hanging astrolabe in precision, and the sextant later further improved upon it; the mariner's astrolabe essentially withdrew from practical navigation in the second half of the 18th century, becoming a museum piece and an object of study in the history of navigation.