16th-Century Mariner's Astrolabe

Timeline

1. c. 1480–1550Lisbon · PortugalPortuguese navigators simplified the Arabic astronomical angle-measuring tradition into a heavy, pierced brass ring, weighted at the bottom to stabilize against the ship's rolling; the sighting vane could measure the sun's noon altitude or the altitude of Polaris to determine the ship's line of latitude.
2. c. 1580–1590Mediterranean · MediterraneanBy the 1580s, the mariner's astrolabe had become standard equipment on Spanish, Portuguese, and Mediterranean merchant ships and warships; unfinished astrolabes recovered from the 1588 Armada wreck sites attest to emergency wartime assembly and widespread use.
3. 1551–1585Seville · AndalusiaMartín Cortés de Albacar's Arte de Navegar (1551) systematically documented the making and use of the mariner's astrolabe; promoted through the Casa de Contratación's navigation school, it transformed latitude determination from individual pilots' experience into a teachable body of navigational knowledge.