The Atwood Sphere is a large planetarium sphere made almost entirely of sheet-metal five meters (~16 ft.) feet in diameter. The sphere is almost entirely enclosed, with one end (or "poll") of the sphere open. Through this opening, a wooden, steel, and plastic gondola, made to carry up to six passengers, is able to enter the sphere on tracks specifically constructed for this purpose. This gondola is mostly made of wood, and has bench seating. It runs along a steel track, driven by an electric screw motor.
The sphere itself is made of steel gores, welded at the seams and reinforced by riveted aluminum banding. The sphere contains 692 individual star holes, drilled by hand and labeled in ultraviolet paint. These star holes are virtually invisible from outside the sphere, but are visible from the inside - when visitors and facilitators are inside of the sphere - due to light shining through them.
This sphere is driven by an electric motor which powers two drive wheels. This allows different star holes (and, thus, constellations) to be visible from inside the sphere at different intervals as it rotates.
Object Story
The Atwood Sphere was created in 1913 by Wallace W. Atwood. Atwood served as the Secretary for the Chicago Academy of Sciences. The sphere is made of galvanized sheet-metal approximately five meters (~16 ft.) in diameter. 692 perforated holes in the metal sheeting of the dome simulate stars that are in principle visibility to the naked eye from Chicago. While those stars are not all visible outside due to the pollution in the Chicago sky, the Atwood Sphere would have given people the opportunity to see all of the stars. The Atwood Sphere has a gray color on the outside, being surrounded by multiple strips of metal. The interior is dark besides the holes showing the different stars and constellations. The Atwood Sphere is technically the oldest planetarium in Chicago.
