Bras astrolabe, 1558.
© Science Museum / Science & Society Picture Library
This astrolabe was made by Georg Hartmann (1489-1564), an instrument maker from Nuremberg, Germany. An astrolabe is in esence a model of the universe that an astronomer could hold in their hands. Popular in Medieval and Renaisance Europe, its many uses included timekeeping, astrology and surveying. It offers a two-dimensional depiction of the heavens, whose layout is achieved using the mathematical technique of stereographic projection. From its origins in the Ancient World, Islamic astronomers developed the astrolabe and its use spread throughout Europe. This back view shows the moveable-sighting arm called the 'alidade', which is used to measure the distance of the stars or for surveying.