Mariner's astrolabe

Common card · No. 472612

The mariner's astrolabe, also called sea astrolabe, was an inclinometer used to determine the latitude of a ship at sea by measuring the sun's noon altitude (declination) or the meridian altitude of a star of known declination. Not an astrolabe proper, the mariner's astrolabe was rather a graduated circle with an alidade used to measure vertical angles. They were designed to allow for their use on boats in rough water or heavy winds, which astrolabes are ill-equipped to handle. It's notable for its role during the Age of Exploration where Portuguese and Spanish navigators used it to great success. In the sixteenth century, the instrument was also called a ring.

Read on Wikipedia · Image Georges Jansoone, CC BY 2.5