The astrolabe is an astronomical instrument used from around the 6th century to measure time and position by determining the altitude of heavenly bodies like the Sun and certain stars. Measurements were taken in reference to the viewer's horizon and the meridian and using a representation or map of the sky with a measuring scale engraved on the instrument itself.
This is a companion discussion topic for the original content at https://www.worldhistory.org/Astrolabe/.