Hoepli's pocket planetarium or star identifier, 1935-39.
© Science Museum / Science & Society Picture Library
This pocket planetarium was devised by Ulrico Hoepli in Milan, Italy. The device consists of a hinged book of circular paper and card star maps with a storage case. Like a conventional planisphere, it is designed to show the appearance of the heavens at any time of the year. In addition, the Hoepli planetarium can be used to show the sky from any part of the Earth. In operation, the user opens the star charts at the relevant map and then places the whole set in the open storage case. The chart is then rotated to the relevant latitude of the user, so that the scales on both map and case correspond.