Chris, fantastic setup. When will you be taking tours? I for one will be happy to drive to Gippsland and pay an admission price, just to check out the setup
Keep the piccys coming, love your work!
Bo
Chris, fantastic setup. When will you be taking tours? I for one will be happy to drive to Gippsland and pay an admission price, just to check out the setup
Keep the piccys coming, love your work!
Bo
Thanks Bo - there have been plenty of friends and family take a look, but it wasn't built as a public facility. Send me a PM if you're coming down this way.
Here's a few pics of the 700 mm deep power cable trench. Dingo hire was $300 for the weekend. It ripped through the soil pretty easily, although is not very stable on a side slope. Where the trench could not be so deep, I capped it with 75 mm of concrete (as well as the orange warning tape, which was laid about 150 mm above the power cable conduit).
Really glad that I went for a 240 Vac supply rather than solar / battery.
We were away for the recent magnitude 5.3 earthquake which was centred only a few kilometres from here, so it was with some trepidation that we inspected our house and observatory upon arriving home yesterday. I'm glad to report that there appears to be no damage to the observatory, and apart from smashed china ware, vases and ornaments; plus books and pictures on the floor, everything seems to have survived.
Before arriving home, I was concerned that the approx 100 kg of mass on the 3 metre pier might have tested the pier-foundation interface beyond the limit, or, that the building itself may have bashed into the upper part of the pier via the edge of the hole in the observing floor (which is about 2.2 metres above ground level). This appears not to have been the case since the electrical cables that pass through the narrow (~5 - 10 mm) gap do not apear to be marked at all. Whew!
I've just checked the polar alignment and it has moved a small amount in an Easterly direction, which is interesting, since most of the stuff affected in the house also moved in an E-W direction too.
I now think that the 188 kg of reinforcing steel that I put into the pier foundation, along with the 2 cubic metres in the block, and the 450 mm dia concrete pier were all well worth it! After all, who designs their observatory for an earthquake?
Good to hear your observatory (& home) survived relatively unscathed.
I wonder if the seismologists at the universities would be interested in your observation about the displacement of your polar alignment??
DT
Thanks David. Maybe the movement is largely based on radial direction from the epicentre? I don't know - I guess that the local geology might also affect the direction of movement.
Thanks David. Maybe the movement is largely based on radial direction from the epicentre? I don't know - I guess that the local geology might also affect the direction of movement.
Chris
Hmmm the missus wouldn't see me for months...
This is the most impressive thing I've seen today (and I've done a lot of surfing)!
Yesterday I went to switch on the observatory dehumidifier and discovered that it was chockers with ants. They had got into every conceivable nook and cranny. After lots of ant-spray, compressed air and water, they're still not all out, but I reckon that I've got 99% of them so far. I won't reassemble it for a few more days yet.
Chris
My dome has been built for over 5 years now, so I thought it time to update this thread by reflecting on the observatory’s design and how well it has worked.
Firstly, some basic stats on the two-storey 5 metre high obs:
Dome - 3.6 metre diameter, geodesic, 105 off 9 mm plywood triangles Turntable – rolled 75 x 75 x 6 mm angle iron running on upturned plastic wheels Walls – 3.0 metres, mini-orb cladding Foundation: - 2 cubic metre reinforced concrete block Pier – 2.2 m x 450 mm dia reinforced concrete pier, with an 1100 mm x 275 mm dia steel pier extension. Mount – AP 1200 GTO Scopes – M14 SCT & NP 127is Observatory construction cost - $7k (excluding equipment)
How well has it worked? Overall, very well indeed. To have one’s scope permanently fixed to a mount on a solid pier saves a lot time and makes the whole experience much more satisfying. Set up time is not much more than 5 minutes. The dome provides great protection from the wind and dew, and also from light pollution. The hinged lower slot door rarely needs opening. The observatory has been used mainly for visual work, with over 150 visitors passing through since it was officially opened in 2009. More recently I have experimented with my DSLR camera taking images through both scopes, but mainly through the 14” SCT. I don’t have any guiding (yet) so generally limit exposures to 1 minute at 3.5 metres focal length. I never see any evidence of wind-induced vibration – either in the eyepiece or in images. It seems that the pier is fairly well isolated from the building too.
The two-storey design is neat and compact, but does involve many trips up and down the stairs; this doesn’t worry me at all but does deter some visitors from venturing up the spiral staircase to the observing floor. Last night, we had over a dozen visitors (typically aged over 60) and they all ventured up. If need be, I can rig up a monitor downstairs to show live images.
Issues: Not surprisingly, keeping water out is the key issue.
(a) Water ingress – mainly through penetrations in the dome –eg. Stand-off bolts for the shutter tracks. Also occasionally through an unknown path onto the dome base ring. I am considering hiring a cherry picker so that I can cover the entire dome in a special mesh fabric and then apply a roof sealing paint – industrial quality. This will provide a longer term fix and help protect the timber construction. The top one-third of the dome’s external surface is virtually out of reach – even with a long extension ladder.
(b) The southern side of the dome gradually attracts mould, which can be wiped off with a sponge and some mild bleach.
(c) The bottom plate of the circular building’s timber frame is also timber, and whilst I used a dampcourse layer between it and the slab, it would have been better if I had made it from hardwood or steel. It might be the weak link in the overall design.
(d) Strong winds have not even hinted at moving the dome itself (~250 kg) but have once partly moved the shutter (> 120 kph). It’s now tied down more securely, and it’s best to keep it closed during wind > 25 kph.
(e) Spiders, ants and other insects have chosen the dome as their home. Maybe I need to get a pest exterminator to spray the whole building.
(f) The width of the dome opening is barely 700 mm, which is great for protecting the observers and equipment from the elements, but another 200 – 300 mm would have made the world of difference for ease of keeping the scopes looking through a clear opening. However, the present arrangement is workable, although a 14” scope on an offset GEM is at the limit. (The pier was offset 250 mm North to allow for the original fork-mounted scope.)
If I were to build it again, what might I do differently?
1. Consider making the building only 3.5 m diameter, so that I had the option of using a ready-made fibreglass dome (that could be automated).
2. Use a different material for the building frame’s bottom plate / ring (refer to (c) above)
3. Cut a wider aperture opening – say at least 900 mm wide.
4. Make the dome about 12 mm larger in diameter than the building, so that the weather seal design is much simpler.
Conclusion – The project has been very satisfying to build, own and operate, and has delighted many a visitor. The home-built observatory, which allowed me to upgrade my equipment considerably, does not come without some on-going maintenance, but the rewards are astronomical!
A small selection of pics showing various phases of the project....which of course, will never end.
Chris
Last edited by ChrisM; 14-12-2013 at 10:29 AM.
Reason: Added some pics
Diameter = 3.6 m
Lower ring (fixed to top of walls) = 100 x 50 mm ply
Upper ring (rotates) = 100 x 50 mm ply attached to a 75 x 75 x 6 mm steel ring rolled to 3.6 m dia.
In the photos, the plywood rings are blue, and the steel ring is red.
Eight plastic wheels are mounted on the lower fixed ring, and the steel ring sits on those wheels. Three additional wheels, spaced at 120 deg around the turntable, keep the two rings aligned.
The cross-section drawing also shows how the 5/8 geodesic dome was attached to the top plywood ring, and how the safety hooks (purple, & 13 off), that stop the dome lifting off the walls, were arranged. The brown-coloured C-section in which the safety hooks operate, was made from about 1.6 mm sheet formed and then rolled.
On the LHS of the sketch, the weather-shield can be seen. A neater and easier design would have had the turntable a fraction larger in diameter so that the weather shield did not require profiling.
After five years in the weather, the dome had deteriorated more than I expected so I have just spent the weekend finishing what I started doing on the Labour Day w/e in March: applying a new paint system to the dome.
After cleaning the dome, I applied a self-adhesive plastic mesh to the entire dome surface. The mesh comes in 1200, 200 & 50 mm rolls, so it was a bit of patchwork application, with plenty of overlapping areas. The paint was Granosite, which is very thick and forms a membrane in and over the mesh. I lost count of how many coats I applied - perhaps 6 or 7 all up, taking 20 - 25 litres of paint. Even with multiple coats, the mesh is not completely filled up everywhere, so I hope the surface doesn't capture too much dirt.
Access was gained via a trailer-mounted 34 foot cherry picker.
Our local astro society has a great observatory but it was originally built for a long refractor and now houses a 14" SCT. So the pier is really tall and eyepiece access is always by mobile stairs. I don't like them and am trying to convince others that an observing floor could be built to enhance operations, particularly for little ones (we use it mainly for public nights).
How high is the top of your pier's mounting plate (i.e. what the mount bolts to in lieu of a tripod) above the level of the observing floor? Are you (and your wife) satisfied with the level, and how tall is the shorter of you?
I see that your stairs are pretty narrow. I think our dome is a bit bigger than your 3.6m. Is that 3.6m to the inside edge of the walls or ring, or the outside walls?
Thanks in advance for a response and congrats on an excellent obsy!
Our local astro society has a great observatory but it was originally built for a long refractor and now houses a 14" SCT. So the pier is really tall and eyepiece access is always by mobile stairs. I don't like them and am trying to convince others that an observing floor could be built to enhance operations, particularly for little ones (we use it mainly for public nights).
How high is the top of your pier's mounting plate (i.e. what the mount bolts to in lieu of a tripod) above the level of the observing floor? Are you (and your wife) satisfied with the level, and how tall is the shorter of you?
I see that your stairs are pretty narrow. I think our dome is a bit bigger than your 3.6m. Is that 3.6m to the inside edge of the walls or ring, or the outside walls?
Thanks in advance for a response and congrats on an excellent obsy!
Cheers,
hamish Barker
Nelson, NZ.
Cheers,
Hamish
Hello Hamish and thanks for your kind words. I saw your post just today so apologies for the delayed answer.
The height to the top of the plate upon which the mount (AP GTO 1200) is fixed is 995 mm. Necessarily, this is a compromise but I think it is a good one for the range of elevations that the scope is used for. Due to lots of trees, I rarely observe below about 20 deg - may be once in a while to show a visitor the crescent Moon or Venus, and on those occasions I use a set of steps.
When observing a target above say 70 deg, I need to get down quite low on the adjustable observing stool. The lowest seat position is 325 mm above the floor, and sometimes that is not quite low enough, but that might be for photographic work with the DSLR, which sits out a little way beyond where the EP would be since I don't use the diagonal with the camera.
Most observers would be in the 160 - 180 cm height range. There is also a fair bit of flexibility to be had just by rotating the diagonal to match their height. There is obviously a lower risk having someone get down a bit lower than having them climb steps in the dark, especially when you don't want them to reach out and grab the telescope should they lose their balance.
The OD of my obs is 3600 mm so the nominal ID is 3400. The stairs were designed to be 600 wide, which is adequate in practice. I didn't want to sacrifice any more observing floor space than essential.
I had a quick look at the Nelson Obs website, and I see what you mean about the tall pier! Good luck with your deliberations.