astrolabon

The astrolabe is an early scientific instrument used for timekeeping and astronomical observations. A common type, the planispheric astrolabe, allowed users to calculate the positions of the Sun and stars relative to the horizon and meridian. It essentially provided a flat representation of the celestial sphere, including key circles like the ecliptic and celestial equator, functioning as a rudimentary analog computer.1

Originating around the 6th century, astrolabes became widely used in Europe and the Islamic world during the Middle Ages. By the 15th century, mariners adopted them for celestial navigation, though they were later replaced by sextants. Typically made of brass or iron, astrolabes featured a base plate (mater) with coordinate lines, a rotating disk (rete) showing stars and celestial circles, and a sighting rule (alidade). The word "astrolabe" comes from the Late Greek word for the instrument, astrolábion.12