This device was purchased in the Czech Republic in the 1990s, shortly after the collapse of the Soviet Union. It had been used in classrooms there and appears to have been custom made by hand, probably early in the 20th century. The inclusion of a flat plane to represent the horizon is an unconventional design. Typical armillary spheres are entirely open in the center. However, this one is designed so that it almost fills the sphere. This device resembles one diagrammed on the Harvard Natural Sciences Lecture Demonstrations website. Portions of their description of its purpose and operation appears to apply this device:
The position and motions of heavenly bodies are projected against a hypothetical sphere of infinite radius, centered on the Earth, called the Celestial Sphere. With this demo you can explain the motions of the stars and of the Sun, and show various aspects of the seasons.
…The spherical wire cage defines the celestial sphere, its pole aligning with the Earth’s north pole and its equator defined as the projection of the Earth’s equator onto the sphere. The Ecliptic is a ring that marks the Sun’s path through the heavens; it is inclined at an angle of 23.5° to the celestial equator. A tilting plane defines the observer’s horizon, which is at 90° to the observer’s latitude…The whole sphere is mounted on a platform that can be tilted to put the observer’s horizon plane can be aligned horizontally; this simplifies things a bit. With the sphere, several basic aspects of celestial motion can be demonstrated.
The Sun moves on the sphere east to west one revolution per day, but also has a long term motion west to east along the ecliptic of 1° per day. The points at which the ecliptic cross the celestial equator are called the Vernal (March 21) and Autumnal (September 23) equinoxes. The maximum elevation of the ecliptic above the celestial equator is the Summer Solstice (June 21) when the Sun is directly overhead at a latitude of 23.5° north, the Tropic of Cancer. The maximum declination below the equator occurs on December 21, when the Sun is directly above the Tropic of Capricorn, 23.5° south. The north-south motion of the position of sunrise shows a maximum northern point on the Summer Solstice, and a maximum southern point on the Winter Solstice.
Note: Our knowledge of astronomy is limited. If you have further insight into the use of this device, we welcome your comments.
Condition: Generally very good with the usual overall oxidation to metal and wear and handling expected for a didactic school device. Some bolts and wing nuts apparently replaced.
“Armillary Sphere.” Harvard Natural Sciences Lecture Demonstrations. 2021. https://sciencedemonstrations.fas.harvard.edu/presentations/armillary-sphere (8 April 2021).