bavarikon4UDescription
The astrolabe is a combination of a rotating star chart, a sighting instrument for angle measurement and an astronomical slide rule. It was developed by Greek astronomers in the period from 150 BC to 150 AD. In the Middle Ages, Islamic scholars improved the astrolabe and made it known in Europe.
The astrolabe can be compared to a rotating star chart. From the south pole of the imaginary celestial sphere, all celestial circles and star positions are projected onto a plane passing through the equator (stereographic projection).
The horizon system's elevation and azimuth lines are shown on a washer, constructed for a specific geographical latitude. Above it is an artistically pierced disc, the rete, rotating around the central axis and containing the most important fixed star positions and the zodiac (ecliptic). A swinging ruler (alidade) with two sighting devices, diopters, on the back of the instrument makes it possible to measure the stars' elevation angles. Various hour and date scales allow for the astrolabe to be used universally to determine positions and time in astronomy, astrology and surveying.