Description
Celestial planisphere

A planisphere is a device that shows the groups of stars (constellations) that can be seen in the sky at any time of the year in a particular location.
Different stars are visible in the sky depending on where you are on the earth’s surface. A planisphere is therefore designed for a certain area, showing the stars visible in that particular latitude zone (the position above/below the equator).

A planisphere consists of a star chart, i.e. a map of the sky, with the days of the year around the edge. The star chart is attached at its centre to a circular overlay with the hours of the day around the edge. The overlay has a window or hole so that only a portion of the sky will be visible in the window at any given time. Both parts are mounted so that they are free to rotate about a common pivot point at their centres. By lining up the correct date with the time of day you will get a map of what you can see in the sky at that time.

Since the planisphere shows the three-dimensional night sky on a flat surface, there is some distortion of distances and/or area, depending on what ‘projection’ is used to map the celestial sphere onto the plane surface.
15/04/2008
Created by: Ruth Horry on 15/04/2008