The Rude Star Finder lets a navigator identify a star from its altitude above
the horizon. It consists of planispheric maps of the northern and southern
skies, the rims of which are graduated to two minutes of time. Each planisphere
has a celluloid meridian arm for determining the declination of stars, with a
slide that can be adjusted for the latitude of the observer. There are in
addition eleven transparent celluloid altitude-azimuth templates for use at
different latitudes up to 66o north and south–that is, over the
greater part of the navigable waters of the globe; a set of pins for marking the
positions of the planets; an instruction brochure; and a cardboard case.
Gilbert Rude applied for a patent for this device in December 1920. This
example was made before the patent issued in December 1921. Rude donated it to the Smithsonian in 1957.
Ref: G. T. Rude, "Star Finder and Identifier," U.S. patent