Bras planispheric astrolabe with Gothic script, 1495-1505.
© Science Museum / Science & Society Picture Library
This unsigned bras astrolabe is thought to be Italian in origin. An astrolabe is in esence a model of the universe that an astronomer could hold in their hands. From its origins in the Ancient World, Islamic astronomers developed the astrolabe and its use spread. Popular in Medieval and Renaisance Europe, its many uses included timekeeping, astrology and surveying. The two-dimensional depiction of the heavens used on this instrument is achieved using the mathematical technique of stereographic projection. This front view shows the moveable fretwork plate called the 'rete', which denotes the positions of the stars by short curved pointers.