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.
Accurate Planispheres represent the Celestial Coordinates: right Ascension and Declination. The changing positions of Planets, Asteroids or Comets in terms of these coordinates can be looked up in annual Astronomical guides, and these enable Planisphere users to find them in the Sky.