In recent years, I've been thinking more of building a back yard observatory. While Tucson skies are okay for a city of nearly 1 million (brightest part of the Milky Way just visible on dry nights), it just isn't suitable for dark sky observing. But there have been lots of times that I've wished there was a ready access scope for checking out a planet or lunar view. It is a real pain to set up a scope out of the house or van, then have to put it away again afterwards. A couple years ago, I even obtained a telescope from the estate of a telescope-maker north of Phoenix - a 12.5" Cassegrain, perfect for such applications. It has patiently been waiting for its moment in storage for construction of a structure. Our back yard is a little small, though, so have been giving some thought to what to build. While one where the roof rolls off is straightforward to build, the supports and frame for the roof while it is off the building automatically doubles the footprint. A dome might be nice, but are expensive in larger sizes, and I dislike the restrictive sky view out of a dome slit. What other options are there?
Sky and Telescope magazine in May of 1993, and the photograph shown here is from that article. The roof panels roll down a rail, while supported by a pivoting strut and counterbalanced with weights inside the structure. David is shown here at left with daughter Julie (now grown) and their builder Andy Orngard who came up with the design. It has no structure outside the building when closed, which fits my desire. However, the steep roof angle isn't needed in Tucson (no snow or ice), and I couldn't figure how to modify it to work with a shallower roof. Another good feature of this design is keeping one side of the observatory up to keep out wind or an obnoxious light.
So I was thinking of something similar but wanted to go larger because of the larger scope and having room for a friend or two. I gave up the rails and tried running off pivoting struts. Using paper and cardboard models in 2D only get you so far, so I decided to make a scale model out of wood, about 1:12. This is what I came up with... Shown at left with the roof closed, it is 10X10 feet inside clearance, and the outer walls are 5.5 feet high, with the peak of the roof 8 feet high when closed. With the roof open, as shown at right, the 2 struts per side rotate the panels up and out alongside the building, providing good horizons in all directions. The little stick figure is nearly to scale for a 5 foot tall person w/a 3" refractor. The roof sections reach a balance point about half way open, so like David's design, would need a counterweight system to aid in starting it opening, and to catch it as it reaches its open limit.
A shown in these pictures, it also works, like David's with one of the roof panels either partially open or closed altogether. Although not shown well, the pair of struts do NOT work off the same pivot. Different pivots points and strut lengths are needed to get the roof moving up off the walls, fully clear the rear wall and then to stay close to the wall when it is open. The struts would scale directly to a full-size building, perhaps aluminum bar stock 4" to 6" wide and 3/4" thick or so. The weight of the roof panels rests on the rear wall via the inside strut when fully open. Pivot axes made of 1" steel shafts could be made into an angle-iron bracket to be fastened to studs in the wall for strength and security. And though I haven't figured out a door yet, the 5+ foot tall walls should allow easy access from outside.
Not wanting to rush into anything, I'll likely dig a hole and put in the telescope pier first, get the mounting installed, and perhaps even the telescope too before building the observatory around it. But I think the design has possibilities. If any of you see why it won't work, let me know or come by and play with my little model with me!
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