7" f/12 iStar refractor 28: Ridged observatory alternative to a dome?

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A ridged, bell ended observatory at a UK public [fee paying] school housing an antique 4" or 5" refractor. This design has the advantage of not needing spherical gores. Though room for the refractor dewshield is more limited [than a dome] up at the peak. Suggesting that it be made slightly taller to compensate.

Unlike a spherical dome, it does not shout; "observatory alert" to the casual observer. Particularly if not furnished with a snow white "hat" like many domes. It could easily pass for a common garden shed to any passer-by. Though the roofing felt does reinforce its [apparently] lowly status.

The ability to rotate is hidden by the form, generous overhang and traditional construction. The base need not be made multi-sided if a cylinder is desired. Cylinders might draw slightly more attention but it could still pass for a grain silo in this agricultural, rural situation. Or, the structure could be somewhere to enjoy afternoon tea in the garden but sheltered from the changeable weather. Octagonal "garden summer houses" are popular in Denmark but usually glazed.

The observing slit is formed by two, long, flat panels. Hopefully with interlocking channels at the joint and hinges to shed rain. The entire "roof" structure rotates like a dome but would ideally need something better than the traditional roofing felt seen here. Otherwise there would be thermal problems as it absorbed the sun's heat and released it later. Not to mention felt's great weight compared with aluminium or even a fiberglass construction. Aluminium panels would need traditional folded seams to look well and remain strong and weatherproof. Wrinkling could be avoided due to the flatness of the panels and [hopefully] some manual expertise.

Skilled, metal roofing workers still exist in Denmark [and elsewhere no doubt] and are known as blikkenslager here. Tin smiths or even tin beaters are usually employed for making metal roof flashing, decorative roof ornaments and dormers. I wonder how much it would cost to employ a tradesman to construct a strong and weather proof shell of this form out of aluminium? It would almost certainly be cheaper than any commercial dome in the 12' size. A skeleton of square or rectangular, aluminium tube would greatly reduce the weight and extend the lifetime compared with the traditional, deep plywood ribs. Not to mention the tubing's smaller section providing rather more space inside.

The image shows a similar observatory erected in New Zealand to house a Cooke 5" refractor.

   Edward George Leonard Morley — 1894 to 1973 Nelson Astronomer | NZETC

A thin, plywood, shell construction is still possible but would be much heavier than aluminium with more thermal issues. The ridged, bell ended observatory is certainly an interesting option. Not least from a historical perspective for housing a "classical" refractor.

Click on any image for an enlargement.

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