Author and planisphere collector Peter Grimwood presents a history of these night-sky navigators in pictures, with a selection of examples taken from the 200 that make up his new book Card Planispheres: A Collector’s Guide.
A planisphere is a map of part of the celestial sphere that can be adjusted to match the positions of the stars in the night sky for a particular time and location.
Initially developed around 200 BC as the metallic ‘planispheric astrolabe’, the modern-day planisphere is usually made of card or plastic discs with a rotating oval ‘horizon’ to reveal the stars visible overhead.
You simply turn the top rotating disc to match the direction you’re facing with the current date and – lo and behold – you get a map of the constellations and asterisms in the sky above.
The basic idea has been around for centuries and, depending who you believe, was invented by Eudoxus of Cnidus (a Greek mathematician), Hypatia (a Greek astronomer) or Vitruvius (a Roman architect and engineer).
Here’s a selection of some of my personal favourites, showing how this simple but effective design has been adopted for astronomers in different regions of the world.
(All images are copyright Peter Grimwood)