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I have come to a number of firm conclusions from using my home-built observatory for a while.
If somebody asked my opinion on an optimal observatory design I'd suggest:
Do build or buy one if you can. Having the shelter has provided me with countless hours of enjoyment in quite a short time. I have been observing the sun for hours and hours when it has been either very cold. Or very windy but blowing from
behind the open dome.
Think about it this way: Divide the
total cost of all your astro kit [without an observatory] by the number of hours of
active use. Don't count the hours setting up and tearing it all down again whenever it clouds over.
You now have a rough cost of your hobby
per hour. Now add the
cost of an observatory. But remember that you are always set up to
observe or image. So your time at the telescope is usually positive and
active. Rather than negative preparation and endless dismantling with
possible damage or personal injury.
If you are retired, like me, you will find yourself in your observatory, actively observing, on far more occasions than you ever did before you had one. The potential of a partially cloudy day, or evening, can be maximised within a few moments of deciding to open up the observarvatory. I find I take far more chances to observe now than I ever did before.
I probably spend more time observing in a week, than I did in a year, when only the cold and windy lawn beckoned. The mental and physical inertia from suffering too many cloudy nights, out on the lawn, can limit one's viewing to a very small total number of hours per year. The cost per
active hour can soar to hundreds, or even thousands, of Pounds/Dollars or Euros per hour.
With a dome you just sit and browse with one eye on the sky while you wait for a precious clearing. As soon as the cloud has gone you stand up and peer through the eyepiece until the next cloud comes along. No panic if a short shower comes over. Close the shutters and browse, read or study until the the next clearing. If you image then you can spend this waiting time optimising your video files.Or posting your results on an astro forum.
NO heavy carrying. NO setting up heavy and bulky equipment nor taking down. NO mounting re-alignment. NO optical re-collimation after dragging the white elephant in and out of doors in a panic. Often in the dark. NO worrying about condensation from taking an icy instrument back indoors. NO more waiting for the inevitable cool down time of the precious optics.
Do make a hemispherical dome of birch [preferably marine] plywood for low thermal mass but keep the ribs light. If you can afford to glass over it with resin then that would be very useful. Better waterproofing and probably another decade of useful life.
An arched dome [half cylinder] is another serious contender for the DIY observatory builder. In aluminium or bendable plywood it provides much more room than a round dome. Easily built in a day or two instead of weeks like a round dome often requires.
Don't be afraid of a friction wheel and crank drive for a non-remote observatory. I can spin my heavy dome, by hand, as fast as I care to. Stepping the dome slit forwards at intervals, to follow the sun over the hours, is so easy and quick. It requires niethier physical nor mental effort. A touch of the hand crank and the dome simply rotates. In either direction.
The secret lies in the 2' long hinged or pivoted beam. With a 5kg counterweight fixed on the long end. While a 4" industrial, urethane roller at the short end, is driven by the bike crank and a cut down, plastic pedal. With a sealed bottom bracket bearing to keep the cranking friction low. The weight rises and falls to let the roller follow the dome's base circle intimately. NO slippage! NO delay. Instant reverse. The image shows a trial set up which became semi-permanent. Until, that is, I can think of a way of making it "prettier."
Make the observatory walls of plywood [or planks] too. Then they don't absorb heat all day long and release it all night when you want to look at the night sky. Plywood sheets also have the unique advantage of triangulating your structure. Saving time and money on complex bracing. They stock grooved, exterior plywood in metric 8x4 sizes in most Danish DIY outlets. The grooves add that touch of sophistication [over plain sheets] and is very long lived in my own experience.
A second choice of building covering would be corrugated metal, roofing sheets. Arranged vertically they provide strength, weatherproofing and security. Ideal for covering a round, [cylindrical] observatory building made from rings of glued and lapped plywood circles and vertical, spacer posts.
Do
NOT build an octagonal building, as I did! The distance across the walls of an octagon is VERY MUCH
smaller than a circle which encloses the points of the angles where the walls meet. You need a MUCH LARGER dome of the size across the
points. NOT the tiny one across the flats. [Walls.] The difference can easily be 3' lost over the
useful, internal diameter.
If you need a raised observatory then DO NOT have a trapdoor in the observatory floor! Have access via a landing outside a proper sized door, or doors. Don't put the access doors towards the prevailing wind! [As I did with both of mine!]
I badly wanted an indoor access ladder to avoid the danger of climbing and descending over months of winter ice and snow at 55N. Most people aren't daft enough to need a double height observatory just to see over their 15' [5m] boundary hedges. It's a [very] long story!
I have been delighted with my two floor, all aluminium stepladder,, with handrails, from day one. It's the sort of thing you see in big shed stores and warehouses leaning up against raised shelves and is meant to last for years. The wide treads are vital to balance and security when carrying bulky or precious stuff. Which a ladder, with narrow rungs, never can.
Don't make your observatory's observation slit too narrow. Be as generous as you can with its open width. Particularly if you use a GEM equatorial. The lateral offset of the OTA narrows the effective slit width dramatically. Because the telescope is always looking out at a skewed angle. Do a scale drawing to confirm this before making any decisions. A fork mounting will usually shrug off skewed viewing angles. Greatly reducing the need to move the dome on to follow an object.
I can't really argue about up-and-over shutters versus laterally moving, bi-parting shutters. Just that I was terrified of losing control of a heavy up and over shutter and completely destroying my building!
The draw slides on my bi-parting, shutter doors are so low in friction that the shutters used to open and close in a stiff breeze. That was before I fitted sturdy, galvanized, sliding bolts to hold the shutters both open and closed.
I can still close one shutter and leave the other open to keep out the worst draughts from gales. An up-and-over shutter could shelter you from a short. sharp shower when half closed. Bi-parting doors are always wide open, right over the zenith above the telescope where the rain seems to come from.
Easily closed completely and very much quicker than an up-and-over.
Imagine being able to shelter your valuable equipment from anything the weather can throw at you in mere seconds. You switch off and turn the key to retire indoors until the next opportunity beckons. NO forward planning required. NO ferrying back and forth. NO removing dangerous weights which leave things horribly unbalanced. You walk away and come back to a user-friendly, ever-ready instrument.
If I can do all this, working entirely alone, at over the age of 70, learning as I went along, with the advice of forum members, then so can you. BTW I built the instruments and the mounting too. With lots more to do. How do you fill your empty hours? I don't have many to waste.
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