Portuguese Mariner's Astrolabe

The mariner's astrolabe, a simplification of the planispheric astrolabe, was one of the greatest innovations from the Age of Discoveries, as it allowed sailors to measure the altitude of celestial objects. In the beginning, it looked like the back of the planispheric astrolabe, but, with the sailors' experience, it acquired a new form. It was no longer composed by sheet metal or wood but made from copper alloys, in order to make it less sensitive to the ship's movements.