Retired from the paid work-force and living in rural Australia, I am returning to a teenage interest 50 years on. Past the farm-development years and thus with more time, I more-or-less stumbled on the fact that telescopes, which had been a pipe-dream in my impecunious youth, were now widely available and (relatively) cheap. Moreover, the old Norton’s Atlas (which I still have – 1959 edition) had been replaced by interactive software available for free on the Internet. Even better for someone with a finite amount of observing life left, there were telescope mountings with controllers which would take over the tedious business of finding objects in the sky and putting them into the eyepiece field of view.
I wanted an observatory large enough to accommodate an 8” Newtonian reflector on HEQ5Pro mount so a 2.4m diameter observatory should, I reckoned, give adequate working space.
I would use any materials already on-farm as far as possible.
Constraints included limited workshop facilities and skills and a DIY ethic which dictated one-man assembly.
Why not a shed with a roll-off roof? I have the luxury of 360o viewing on my chosen site and down to 5o above the horizon except for the NW sector where I still can go down to 20o. A telescope within four walls is more restricted in its available sky, although I understand that in an urban site other factors may impose more limitations. My second reason for something like a traditional observatory is that observing through a slit is more comfortable in this often windy and cold (in the winter) part of the country. Dome
Working with the precision required to build the classical hemi-sphere is beyond my capabilities. Straight sections as tangents to the desired size of dome seemed feasible as in the diagram in the first photo below. An eight-sided design was suggested by the roof of my grain silo (second photo). The construction of a flat circular track was beyond my skills and would also require a fair bit of material even if made up of small sections. A flat track also requires guide wheels or a channel form. Importantly, a dome just sitting on a track needs to be secured when not in use: I have read several sad stories of domes blowing away!
On the other hand, a narrow track on which the dome ran on gate wheels (wheels above and below the track to take care of guiding and security) would be within the capacity of a local steel fabricator to roll out of relatively inexpensive mild steel. An additional advantage was that I could mount the track in a way which would allow it to flex enough to take care of any minor deviation of dome or track from a perfect circle. One of the wheel assemblies on the track is shown in the next photo.
Weight was a major consideration both to keep the dome as easy as possible to move by hand on its track and also to meet the one-man construction requirement. Steel was chosen (a) because I am used to working with it, (b) the necessary tools were available (c) it is relatively cheap and readily available. Data on the Internet allowed me to calculate the weights of various options. The lightest galvanised iron (actually probably Zincalume®) – 0.4mm thickness – was used for the cladding.
Observing Slit
Hinged doors would upset the balance of the dome and anything more elaborate would be a headache to make water-tight, so the simplest solution seemed to be a panel section that could be removed entirely for the observing session.
The question was how wide to make it. A full one-eighth section (1m) seemed, on the drawing board, likely to compromise the design. I decided on 600mm as that would be about 28o of azimuth. Obviously, the slit would have to be parallel-sided and open to the meridian, both requirements which would create some tricky angles with the rest of the structure. Pier
Something as solid as a good tripod, well-set in the ground, separated from the floor and of a height which would place the eyepiece of a Newtonian ‘scope on a GEM mount at a convenient level for my eyes (1200mm). I used 100mm dia. medium steel pipe 2100mm long filled with concrete and set into the ground 1200mm in a 200mm dia. hole back-filled with concrete.
I had a supply of second-hand corrugated iron for the walls. Relatively cheap light RHS was used for the posts and purlins. Towards the top of each of the 8 posts a short section of RHS projected inwards to make a sliding connection with smaller-section segments welded to the track. The intention of this way of supporting the track was to allow movement to accommodate any small errors in the circularity of the track and the positioning of the posts and also of the wheels on the dome to eliminate any chance of binding or jamming. For the same reason, instead of a fourth set of wheels, I installed a home-made roller which would cope with any deviations as the dome rotated on the track. The door was fitted in the NE section of the wall, this sector being the least likely direction of driving rain. The home position of the slit is also in this sector. Concrete Floor
Because of the sloping site and the requirement to make the lowest point 100mm above ground level (to avoid any risk of moisture problems) this needed 1.5 cu. mtrs. Of concrete, ballasted with some rocks. A 300mm collar separates the floor and pier. Insulation
25mm polystyrene sheeting glued with Fast Liquid Nails® on the inside of the dome, slit door and walls. Finish
The concrete floor is covered in rubber conveyor belting with carpet on top. Three shelves are fitted around the walls. Cost
N.B. A commercial observatory of this size, including base, sub-floor and pier would be $15,000 upwards. The materials I had to buy plus the cost of the track fabrication came to about $1100. Obviously, the second-hand material I had lying about and my labour was “free”.
Brent, Steve and Matti
Thanks for the comments. I certainly am enjoying the sky, cloud and moon permitting - I am not up to the all night sessions I used to do with mates 50 years ago!
Cheers and clear skies (well after some rain for us farmers)
Thanks, Phil. It works well on those nights when the moon and the clouds are both absent - about 2 nights a month on average! I think we are just too close to the river and the mountains to be an ideal site, but at least Canberra is only a faint glow in the SE. Cannot complain about rain, however, because every fall puts back the effects of the El Nino a week or so.
)...but looks effective Kev 
... and I hope it rains for a week every full moon 
