FORUM

Amateur Domed Observatories:

Why do so called leading amateur astronomers insist on outmoded and inappropriate dome designs and fabrication methods?

What few books there are devoted to the subject are largely filled with the idiosyncratic notions of DIY enthusiasts rather than engineers. People I refer to as experts in make-do-and-mend, i.e. the "Bodgeologist".

The most practical articles written on the subject are still only to be found in Sky & Telescope's former Gleanings for ATMs columns, the Scientific American ATM handbooks edited by Albert Ingalls and the ATM Journal. Needless to say "our" homegrown "experts", raised on a heady diet of lickspittling Paddy Moore, have little of practical use to contribute - it merely being a regurgitation of reprocessed Mooreisms. (So far is their tongue firmly rooted that they need major surgery to say anything)

Take for example the latest Springer-Verlag book, "Small Astronomical Observatories" edited by Patrick Moore, and to judge by the contents, edited is a somewhat loose epithet. Here we find all the usual BAA suspects. Of the dozen domed observatories described only two are metal, and only one dural, and that of course is a dome built by the late Alan Young for Torquay Boys Grammar School. The dome and shutter drive are my design, but naturally Moore doesn't acknowledge that trifling detail.

A distillation of this potpourri became the subject of Maurice Gavin's outgoing BAA Presidential Address in October 1997. Sadly, despite his attempts to provide any useful pointers, it is disappointingly rooted in the make-do-and-mend tradition of post WWII English amateur astronomy. Gavin purports to be sufficiently well versed in the practicalities of this topic to benefit us all with his wisdom. And yet it cannot be said that he exhibits a "Raven's" knowledge of the subject. Is it not time to move on from post war austerity for austerity's sake one asks? If it is acceptable to shell out £15000 on a new motor car, what is wrong with spending the cash on a decent telescope and observatory and using the bus?

Only Chris Kitchen's advice is really worth heeding, especially his remarks on wind loading. Yet one wouldn't expect a BAA President who had spent his entire career as an architect, and appends MRIBA to his monicker, to be able to include in his dissertation, anything about the determination of dome wind loadings, would one?

Chris Kitchen comments after describing the succession of domes the University of Hertford has had over the past 25 years, that though it may cost more, a metal dome is more durable, robust and easier to maintain. But the Ash domes he recommends are far heavier than needs be because Ash insist on fabricating them from galvanised steel sheet. Eventually the galvanising at the joints, dome lip, and shutter guides, wears, and the steel begins to rust. Where the sheet is drilled for fasteners, the steel is exposed and provides a corrosion site. Phase changes in the metal at welded joints and acute bends also leads to internal stresses and electrolytic corrosion. Only duralamin resists these physical processes, and it is, weight for weight, the same price as mild steel sheet. Yet it is has twice the strength to weight ratio and is much more readily formed. That is why it is still the material used to skin subsonic commercial aircraft.

Manufacturing a duralamin dome requires some shop work, but the work is rudimentary if you follow my designs. There is nothing time consuming about it. All the laborious on site assembly work can be done by any D.I.Yer. The cost of my 121/2ft. dome in 1986 was £1200. This included £600 material costs for the dural sheets and the mill rolled rail tube. The wall cost a further £400. I would estimate present day costs at roughly twice this sum.

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