Sphères..

Rare print of an armillary sphere, which is basically a skeletal celestial sphere with a model of the Earth or, later, of the Sun placed in the center. It is useful as a teaching tool and as an analog computer for solving various astronomical problems to a crude degree of accuracy.
Armillary spheres were developed by the Greeks in antiquity for use as teaching tools. In larger and more precise forms they were also used as observational instruments, being preferred by Ptolemy.
The Armillary sphere consists of two major components, the sphere and the stand. The heart of the Armillary sphere is the sphere itself, which was often made and used alone.
The central body in the sphere represents the Earth, which was, of course, considered the center of the Universe. The colures and the Equator (the rings defining the sphere) represent the firmament, that is, the sphere upon which the fixed stars reside. The band going around the sphere, at an angle to the equator, represents the zodiac. The line running through the middle of this band defines the ecliptic. The width of the band is ideally about ±9° to include the wandering of the Moon and planets above and below the Sun's path. The various constellations of the Zodiac also fall along this band. °