A planisphere is a star chart analog computing instrument in the form of two adjustable disks that rotate on a common pivot. It can be adjusted to display the visible stars for any time and date. It is an instrument to assist in learning how to recognize stars and constellations. The astrolabe, an instrument that has its origins in the Hellenistic civilization, is a predecessor of the modern planisphere.
Read more about Planisphere: Summary Description, History, The Star Chart, The Upper Disc, Coordinates