THE DOME

The dome at the top of the observatory houses our telescope.

THE ORIGINAL DOME

Construction of the original dome was another contribution of the FCAS members. A committee designed the dome, and donations from nearby companies were used in the construction. "Lightweight" steel I beams were used for the framework and covered with a silo-dome skin. The shutters were of the "bi-parting" type and it was quite some time before they were hitched up to a hand crank which opened both at once. In the meantime, they had to be opened by hand, climbing a ladder to the mid-point and pushing them aside. In the spring, birds tended to make nests in the tracks which would fall into the cover, preventing the dome from closing until someone could clear out the mess.

This original dome was extremely heavy and rotating it proved to be a problem; at first, a pry bar was used to move the dome, and only in small amounts. Then a member brought in a small winch which could be used to pull the dome. This still was not satisfactory, so he replaced one of the support wheels with a driven wheel, and at last a fairly satisfactory drive was in place. There was one problem in that there was a high spot in the bottom dome ring, so the drive had to be helped past that spot. A manufacturer of turntables for displays such as automobiles was engaged to motorize the dome. On their first inspection trip, they stated that all the "junk" in the middle of the room would have to be removed so that the drive motors could be placed there! They eventually came up with the idea of fastening a rubber-and-fabric gear belt to the inner edge of the dome to engage a drive gear. FCAS members drilled innumerable holes in the steel base ring of the dome to fasten the belt, which was then glued and screwed in place. It worked fine for a while, until the heavy pull on the gear belt and differential expansion of the steel versus the belt caused it to loosen. Usually only one end of one segment would come loose (in the dark) and then the dome wouldn't rotate, or would go only in one direction. While this mechanism did work, it rotated the dome rather fast. This was fine for observers, but we soon noticed that cracks were developing in the masonry supporting the dome wheels.

THE CURRENT DOME

All of these problems resulted in us having to look for a better dome. By this time, actual observation domes were manufactured by companies - we chose the Ash Dome Company of Plainfield, Illinois. Their product appeared well designed and well constructed, and their domes are in use at observatories all over the world. Funds were provided by the Museum from a bequest left them by Bill Blackwood. Installation of the new dome required removal of five courses of brick from the top of the Observatory tower, and construction of a reinforced concrete ring in their place. The old dome was propped up and the removal of masonry was done by FCAS members. A contractor installed the reinforcing steel and the concrete forms, and poured the concrete for the new ring.

The parts for the new dome were painted before assembly, and members assisted the engineer from Ash Dome who came to supervise the job. The dome had been completely assembled at the factory, so all parts and holes lined up (sometimes after a little persuasion), and the job was completed in two days. The new dome has a shutter made in two parts, the larger of which moves up and over the top out of the way for observing. The hoisting of that shutter and placing it on its tracks was the most difficult part of the entire operation, since it is the largest single unit of the dome. The lower shutter hinges down and outward.