25.03.2021 Observation slit mock-up for scale.

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Later I mocked up a 1m wide [39"] observation slit. Using a few arcs to represent the 3D shape at the [missing] front of the dome. This area forms the open doorway of the original "igloo" calf shelter. The doorway consisting of a straight, downward cut removing a section of the hemisphere. A narrow, slanting edge to the moulding helps to avoid rain running straight down the dome and being blown inside. 

A galvanized steel, tubular arch is provided to reinforce this front edge. Which I fitted to help stiffen the dome as I continued to play at DIY dome construction. I could have used the supplied screws but chose to clamp the square, steel pipe, temporarily in place. The arc will be discarded upon completion of the modifications. Or, I might use just the outer sections of the arch beyond the open observation slit for extra strength.

A 1m wide slit may be slightly too wide for my own tastes. Even though it represents only a 1/4 of the dome's diameter. The general guidance online seems to be 1/3 of the dome diameter. My hope is to use "waste" dome material from the "spare," top segment to fill the open [triangular] gaps. This will use what is left of the roof /top segment. After I have cut out the long strips for building the bi-parting shutters. 

There will also be other offcuts. Which might be joined together. To ensure a fully spherical closure of the open triangles for cosmetic reasons. A flat plywood closure of the open triangles is easily possible. It could even have its own, lower slit doors, or shutters. Though a solid, waterproof shelf would be needed to throw the weather outside the supporting building. I just prefer the appearance of a uniform, curved surface. All over, in the same colour and smooth, GRP gel coat finish.

The sheer sense of scale of the new dome shocked me as I sat inside. In the semi darkness, on my low, camping stool. With my back nearly against the opposite "end" of the dome from the opening. The plywood arcs seemed so incredibly distant!

Much less so, once I added some scrap ply to simulate closing the shutters. Which [interestingly] made the shutters look much narrower than when they were wide open. No doubt the dome will appear even larger on completion. When it is finally perched on top of the 1.5m [5'] observatory walls and its 8" [20cm] high, rotation rollers. 

As to human scale I can only just reach the zenith with my finger tips. While I am standing on tiptoe on the bare ground right in the middle. With the dome raised on blocks with an average height of around 15cm or 6" at the midway point. The ground is sloping but the dome skirt is quite accurately levelled by my 360° laser. 

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