Planisphere

Philips' Planisphere, ca. 1900

In astronomy, a planisphere (/ˈpleɪ.nɪˌsfɪər, ˈplæn.ɪ-/) 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 for a given latitude. It is an instrument to assist in learning how to recognize stars and constellations. The astrolabe, an instrument that has its origins in Hellenistic astronomy, is a predecessor of the modern planisphere. The term planisphere contrasts with armillary sphere, where the celestial sphere is represented by a three-dimensional framework of rings.

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