3m [10'] half-cylinder, aluminium observatory.

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With the calf domes weighing in at 250kg or nearly 500 lbs I really had to find an alternative. After endless messing about with full scale models I decided The Pulsar 2.7 just isn't big enough. The next step up is to 10' or 3m. 

My wife agreed that it would be the better option because I could build something to exactly suit my needs, rather than accepting simply what was available. The budget which was formerly going to be invested in the calf shelter or the Pulsar would probably be halved. Simply by doing most of the construction work myself.

Image "borrowed" [for educational purposes] from the remarkable Astronomy Center UK website where there two examples of the semi-cylindrical observatory type are shown.

 http://www.astronomycentre.org.uk/index.php/members-gallery/the-dome/equipment

http://www.astronomycentre.org.uk/

What I could not do myself, at least not with any degree of certainty, was bending the long, half circles of aluminium angle. These would help to reinforce the inner and outer edges of the half cylinder 'dome'. So I cycled off to a small metal fabrication company some ten miles away who had been helpful with materials in the past. A simple drawing showed what I needed and I ordered some more alu. angle to make the rest of the framework. They have a sophisticated, powered bending machine which would ensure the half hoops would remain flat in the other dimension. So that the adjoining vertical walls will be flat.

Keep it simple and get it done! This is the new order of the day. I have wasted years longing for an observatory and not having the budget, nor the skill, tools or materials, to do what I really wanted. Not to mention those huge birches being right in the way!

The observatory will be a simple aluminium half-cylinder mounted on a tall, grooved plywood box to match the shed. It will rotate on small rubber wheels with decent bearings. Two shutters will part in the middle to lie close to the curved roof of the half cylinder. Unlike a hemispherical domes the bi-parting shutters on a semi-cylinder do not extend "out into the wind." Remaining almost flush with the outer areas of the cylinder as they slide horizontally to leave the slit wide open to allow the telescope[s] to see the sky. Probably an improvement compared to the poorly balanced, up-and-over shutter design. Which needs great care to avoid being 'dropped' in either direction. 

I have already started clearing and roughly leveling the [semi-woodland] ground where the observatory will be sited. The death toll was only one leggy shrub and one very skinny sapling. Unfortunately the ground slopes away from the shed as well as being about two feet lower than the adjoining parking area. It was once dominated by two very tall birches which rained twigs, leaves and seeds constantly over the entire back garden. The heavy 'rounds' which I chainsawed from the tall birch trunks have been moved out to the edges of the area. The ancient and rusty tin trunk still contains PVC drainage off-cuts saved for a 'rainy day' almost 20 years ago. Somehow it had become lost and forgotten over the years.

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