Usually a ball representing the Earth or, later, the Sun is placed in its center. It is used to demonstrate the motion of the stars around the Earth. Before the advent of the European telescope in the 17th century, the armillary sphere was the prime instrument of all astronomers in determining celestial positions (from wikipedia).
This is a high detail model. Comes with Diffuse, spec, bump and reflection maps. Works with Max 8 or higher. Textures and model are very hirez for close up renders but can easily be reduced. A must have desk accessory for any mad scientist or adventurer.