We will conclude this introductory chapter, before getting on to the business of planning the observatory itself, with a summary of some of the equipment and accommodation options available for different types of astronomy.
For some purposes, notably, wide-field photography or imaging and observations of astro-atmospheric phenomena such as meteors, aurorae and noctilucent clouds, and visual observation using binoculars, including such useful work as the visual monitoring of brighter variable stars, there is no real need for an observatory, as only lightweight or simple equipment is involved, though some measure of shelter from wind may be desirable for the observer and equipment.
Study of the bright objects in the solar system, either visually or electronically, requires a high resolution telescope, ideally above 15 cm (6 in.) aperture and at least f6, even better, f10 and above. Such a telescope and associated equipment is not going to be easily portable, and many observing opportunities will be lost if it is not permanently set up in an observatory, both through the actual time the setup takes, and the reluctance of any sensible person to spend half an hour setting-up only to find at the end of that time that the clouds have rolled over again. Telescopes used for lunar and planetary work will generally be long-focus Newtonians and the various forms of catadioptric scopes and Cassegrains. Refractors above 15 cm aperture are rare and very expensive.
Visual observation of the deep sky is easy and convenient with a short-focus Newtonian on a Dobsonian mount, and such an instrument need not be in an observatory, as it is fairly easy to disassemble and store, but it will be limited basically to visual observation at low powers. For the larger Dobsonian, many will still wish for the convenience of an observatory, with the option of occasionally dismantling the telescope to take on holiday to a darker sky, or to one of the "astro camps" which are now such popular gatherings. In an observatory, the Dobsonian maybe more easily developed into a more sophisticated computerised observing platform, if desired.
Imaging of the deep sky can be carried out with a relatively small telescope and a good mounting, but the quantity of ancillary equipment, cabling and computers required will soon make temporary setting-up a chore, unless one is lucky enough to live in a rather predictable climate. Accurate polar alignment of an equatorial mounting will have to be performed each time, and it will never be as accurate as it would be in an observatory, in which it can be gradually perfected over time. In addition, other adjustments, such as dual-axis balancing, will have to be made each time, and moreover, reflectors and catadioptrics lose precise collimation when they are moved, and this has to be reset more frequently in a portable set-up than in an observatory (the small refractor scores here, as not generally needing collimation).
If imaging of the smaller deep-sky objects, such as planetary nebulae and globular clusters, is to be attempted, we are more in a high-resolution regime, as with planets, best results requiring large apertures and very heavy and stable telescopes and mountings, and again a permanent site becomes a necessity. A portable telescope, even on an excellent tripod, can never be as stable as one on a properly-built permanent support. It is not totally necessary to have an observatory structure around a permanent telescope site, and this possibility will be dealt with in Chapter 3. For our purposes, an observatory is any fixed observing site, whether or not walled or roofed-in any way.
The study of double stars, either casually, or for purposes of precise measurement, which has not been mentioned so far, also requires, optimally, a long focal length instrument, which can be of any type, so long as the effective focal ratio can be taken into the region of f20 and above with amplifying lenses (Barlows, Powermates or relay lenses). Traditional long-focus refractors, and the various types of Cassegrain, score well here, and again, a very solid, permanent base is almost essential.
The reader should now be in a position to decide whether an observatory is an appropriate solution for his or her needs. In most cases it will be. It is now necessary to consider exactly where it should go, and how to go about making it acceptable to everybody else.
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