Large Hindu planispheric astrolabe, 1870.
© Science Museum / Science & Society Picture Library
Detail of the moveable fretwork plate called the 'rete' on the front of the astrolabe, which denotes the positions of the stars by short straight pointers. Made by Sivalala, this large copper astrolabe with Sanskrit script was commisioned by Raja Ramasimha in 1870. 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.