Amateur Observatories

Some excellent modern telescopes are portable, but obviously a permanent observatory is much better; carry telescopes around, and it is only a question of time before something is dropped. A dome is ideal, but is not easy to make. The design which I would not personally favour is that in which the dome revolves; there is so much mass to be moved that jamming is inevitable. In a better design, only the top part of the dome revolves. The main trouble arises from the need for a circular rail.

Run-off sheds are much easier, and in general are perfectly satisfactory. My own is made in two sections. Each run back on rails that are connected in (angle-iron will suffice if need be). The shed itself is of wood, but hardboard is satisfactory enough. If the shed is made in one piece, one has to have a door at one end, and this, in my view, is not a good idea. If hinged, it will flap awkwardly; and to remove it entirely is not easy when one is working in the middle of the night and one's hands are cold. Moreover, any sort of door may tend to act as a powerful sail in high wind. The construction of a two-piece run-off shed is a sheer problem in carpentry, and the photograph should give adequate guidance.

Another method is to have an observatory in which the roof is run back on rails - the ends of the rails being supported, or by being fixed to the tops of poles concentrated into the ground. If this pattern is adopted, it is wise to make the roof as light as possible; plastic will suffice. The run-off roof idea is best suited for refractors, which have to be higher than reflectors and for which a run-off shed would need to be inconveniently tall. Remember, wind-force is a factor to be borne in mind.

Great care should be taken in the choice of a site for an observatory. According to the principle of Spode's Law ("If things can be awkward, they are"), trees and houses are always in the most inconvenient possible positions. If you can, select a site which is not only away from obstructions, but also well away from artificial lights, and from houses - that will give out warmth, so ruining definition. Above all, never put an observatory on top of a dwelling-house; flat roofs may look tempting but are to be avoided. A rooftop observatory has the worst of all possible worlds. It will experience the full force of the wind, and there will be so much warmth rising that no useful work will be possible.

Inevitably, the available sites will be far from ideal; and it is a question of making the best of things. For instance: if you are interested chiefly in the Moon and planets, select the site with the most favourable southern horizon. Inconvenient artificial lights can sometimes be screened. Even in my home in Selsey, within sound of the sea on the Sussex coast, I have had to put a screen in my garden to shield one awkward street-lamp. Reluctantly, I rejected the idea of using an air-gun to extinguish it permanently!

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