Mariner's Astrolabe

Mariner’s astrolabe marked the beginning of astronomical navigation and were virtually absent from any ship.
This mariner’s astrolabe is a device cast from heavy bronze that is divided into four quadrants by four
spokes. The “alidade” can be rotated around the middle point. It has two “viewers” for sighting a star. They are two vanes with small holes drilled in the middle and which line up precisely with one another. The alidade serves as a pointer that indicates the measured angle on a scale that is engraved around the outer
edge of the instrument. The instrument also has a ring by which it can be kept plumb. In order to avoid being blinded when sighting on the sun, the instrument was held just above the ground and the alidade set in such a way that the sun’s ray passed through the two viewers to produce a point of light that appeared on the ship’s planks.
Very few objects of this kind have survived. There are only about 60 known examples in the world today, most of which were found on shipwrecks. The example exhibited at the Deutsches Technikmuseum was
found in 1980 by fishermen just off the coast of the southern Spanish province Huelva near the city of Cadiz. It is of Spanish or Portuguese origin and was manufactured around 1600.