I go to a lot of museums, and thought I’d start an occasional column about unusual objects.
This is a planisphere, a star chart-computing instrument that’s in the form of two adjustable disks which rotate on a shared pivot. It can be adjusted to display the visible stars for any time and date. It is an instrument that helps to teach how to recognize stars and constellations. The astrolabe, an instrument that has its origins in ancient Greece, is a predecessor of the modern planisphere.
The astrolabe crops up as a key plot point in Bryant & May’s ‘Seventy Seven Clocks’.