n.
Type of early scientific instrument used for reckoning time and for observational purposes.
Astrolabes can be traced to the 6th century AD; they came into wide use in Europe and the Islamic world in the early Middle Ages and were adopted by mariners by the mid 15th century. One widely used variety, the planispheric astrolabe, can be regarded as a rudimentary analog computer. It enabled astronomers to calculate the positions of the Sun and prominent stars with respect to both the horizon and the meridian.
Rete side of an iron astrolabe made after 1582.
By courtesy of the Peabody Museum of Salem; photograph, M.W. Sexton