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Just wondering - why not use a cylindrical shape instead of a dome? Other than the fact that domes are cool...

Just giving this a brief amount of thought, a cylinder (actually a segmented cylinder obviously) would be much easier to build, by several orders of magnitude. It could be capped by simple plywood with some support ribs. It could still be rotated on a track, and adding the viewing slot would be easier as you could just remove part of one of the segments, not cut though a bunch of tria's in a dome...

Thoughts?

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Having a hard time picturing what you're thinking ...probably just me, but can you give it another try or perhaps a simple drawing? thanks! -Tim

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..at least it eliminates the need for the complex dome shape and that building nightmare...

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..at least it eliminates the need for the complex dome shape and that building nightmare...

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thanks for the sketches! My first thought, being from Maine, would be the "snow load" considerations for both the flat top dome and the flat top warm room area. -Tim

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I thought about that as well... I'd likely put some peak to the warm room area... still working on what to do for the top of the obs. area..

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I like simple cylindrical shapes. Here's my little sketch.

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I like this a lot...

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Gastrol, wouldn't the whole building have to rotate based on your design?

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Stashed away somewhere I have some papers written about wind tunnel testing of enclosure designs which demonstrated fairly conclusively that the most efficient (or least inefficient) aerodynamic shape is a flat-sided cylinder with either a flat or sloping top, such as used by the VLT, JCMT, Subaru, et al.

Due mainly to uplift factors, the classic hemispherical dome shape was either second or third best choice. (I will try to find links to those papers.)

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Just wondering - why not use a cylindrical shape instead of a dome? Other than the fact that domes are cool...Just giving this a brief amount of thought, a cylinder (actually a segmented cylinder obviously) would be much easier to build, by several orders of magnitude. It could be capped by simple plywood with some support ribs. It could still be rotated on a track, and adding the viewing slot would be easier as you could just remove part of one of the segments, not cut though a bunch of tria's in a dome...Thoughts?

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Have you built a dome or observatory "would be much easier to build [a cylindrical 'dome'], by several orders of magnitude" = mild exageration maybe

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As much as I love domed observatories I have to say that in most cases for amateurs, it is my opinion that low-mass roll-offs with good ventilation are more practical, more affordable, more reliable and more effective.

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If you ignore the downsides - 1]little or no protection for user and instruments; 2] dew; 3] local light pollution If you need to be under-the-stars just step outside [your dome] and you have the best of both worlds

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Kielder Observatory is really cool.
Do be honest, domes are a bit dorky looking.
Only thing I do not like about Kielder Observatory are the doors. Sliding doors will look way better. Something like Subaru has.

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square edge creates turbulence and becomes a point where wind energy is transferred to the observatory structure, usually creating vibrations with a number of different and often interfering harmonic periods.

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Amateur observatories are relatively tiny structures. If square edges are so bad, why are we not living in mud and/or brick iglu

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Kielder Observatory is really cool.
Do be honest, domes are a bit dorky looking.
Only thing I do not like about Kielder Observatory are the doors. Sliding doors will look way better. Something like Subaru has.

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square edge creates turbulence and becomes a point where wind energy is transferred to the observatory structure, usually creating vibrations with a number of different and often interfering harmonic periods.

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Amateur observatories are relatively tiny structures. If square edges are so bad, why are we not living in mud and/or brick iglu

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LOL!

It is best to think of observatories as machines, not domiciles.

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That depends upon the owner and operator.

A large professional organisation such as ESO may consider its observatories to be machines, but the OP (and most others posting here) probably views their observatory as being part of their hobby.

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The discussion appeared to be mainly centred around the idea of amateur astronomers constructing cylindrical style enclosures rather than the more traditional domes.

Various studies by professionals indicate and conclude that the classic dome enclosure may not be the best design or choice for an observatory, with cylindrical or semi-cylindrical designs being more efficient in many ways.

Such structures have been employed very successfully by the likes of ESO et al, and there appear to be few valid reasons why amateurs would or should not also adopt the design instead of the traditional dome.

Whether or not the very expensive professional observatories should be considered to be "machines" is a little beside the point in this case, IMO.

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Yes, that's the point: for the most part, direct comparisons between amateur and professional observatories is - dare I say it? - pointless.

However, the advantages and disadvantages of the basics of the enclosure designs being discussed generally apply to both professional and amateur users alike.

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Hi Christopher,

There are quite a few amateur observatories from way back that had rotating tops that were not domed.

I have been inside a small observatory with a flat top and it seemed to work fine. It was like Patrick Moore's flat top and the one in your sketch. A slight pitch would help avoid problems with water puddling and make it easier to clear snow.

The famous solar observer W M Baxter used a rectangular shed with a rectangular pitched roof that rotated. You can find pictures on the web. I suspect this would be a more water and snow proof arrangement than the flat top but he never needed to access the zenith.

If you have second thoughts a dome or dome-like top isn't that hard to make. Maurice Gavin's (nytecam) dome is simple, lightweight and durable.

Cheers,

Keith

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I am not against cylindrical, hemispherically-domed, roll-off, clamshell, turret, garden, tent or any other kind of observatory. In fact I love all kinds of observatories and that is part of why I became a professional engineer. And although I believe that roll-offs are generally the best kind of observatory for most amateurs, I chose instead to build my own personal observatory as a 4 meter fiberglassed geodesic dome.

My only desire has been to share objective information about observatory design and how different approaches compare from the perspective of a professional engineer. If I list some of the negatives of any particular observatory design, it does not mean I summarily dislike that design or am exclusively in love with a different design. The profound variety of observatory designs that exist is testament to the fact that there is a vast number of ways to skin this particular cat!

I wonder what I keep doing wrong to keep giving people the wrong impression about my intentions.

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I wonder what I keep doing wrong to keep giving people the wrong impression about my intentions

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As you are, as stated, a professional engineer and I'm a [professional] architect our opinions in this amateur forum are not gospel as many choose to explore their own design route and construction skills with quite different expectations in the final result.

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By the way, your airfoil idea would cause major problems when the wind direction shifts, unless its movement was independent of the slit position.

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Yes - as I mentioned previously, the airfoil and the "observatory" would rotate independently of each other, the airfoil continually pointing into the wind, and the observatory (dome, roof, etc.) tracking whatever it chooses..

Image a weather vane - that continually turns into the wind - but scale the central shaft up and put the observatory in it... The actually mechanics of the airfoil pointing would be very simple. An encoder mounted on a weathervane to register the wind direction, then fed into a control system for the airfoil rotation...

It may very well be pointless - but I thought it was an interesting idea nonetheless... Sometimes Engineers do things just to see if they can...

As to attaching the roof to the cylinder - see my previous post and drawing about the 2X12 octagons for the track.. just use one for the top and cover it... As to an angled roof - not sure if I would go that route or not... I'm thinking of some sort of hybrid with a pitch to the top... but I have several thoughts...

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By the way, your airfoil idea would cause major problems when the wind direction shifts, unless its movement was independent of the slit position.

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Yes - as I mentioned previously, the airfoil and the "observatory" would rotate independently of each other, the airfoil continually pointing into the wind, and the observatory (dome, roof, etc.) tracking whatever it chooses..

Image a weather vane - that continually turns into the wind - but scale the central shaft up and put the observatory in it... The actually mechanics of the airfoil pointing would be very simple. An encoder mounted on a weathervane to register the wind direction, then fed into a control system for the airfoil rotation...

It may very well be pointless - but I thought it was an interesting idea nonetheless... Sometimes Engineers do things just to see if they can...

As to attaching the roof to the cylinder - see my previous post and drawing about the 2X12 octagons for the track.. just use one for the top and cover it... As to an angled roof - not sure if I would go that route or not... I'm thinking of some sort of hybrid with a pitch to the top... but I have several thoughts...

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Unfettered brainstorming is one of the most fun things in the world to an engineer!

If anybody were to ever ask me about the best features of an observatory (no amateur ever has) I would list the following:

1. Intelligent thermal management.
* No big heat sources inside of the observatory.
* Minimize *all* heat sources inside of the observatory.
* Every watt of electricity used in the observatory is a watt of heat generated in the observatory.
* Ability to be pre-cooled to the predicted night temperature.
* Low mass structure.
* Active air flow shutters and high-efficiency (squirrel cage) fans.
* Ability to react rapidly to changes in air temperature.
* Avoid placing observatory on top of a hot existing structure.
* Avoid placing observatory near other hot structures.
* Having a partitioned or separate, heavily insulated control room can really help with heat issues.
* Heavy concrete pads act as heat capacitors that are always out of heat-phase with the environment.
* Hollow concrete piers can be just as rigid as solid piers and with a great deal less concrete and thermal mass (concentric sonotubes.)
* Seeing is cumulative. City dwellers benefit just as much from effective thermal management as do country dwellers. Don't needlessly throw away any.
2. High reliability with failsafe features.
* Make sure that you can always close your roof/shutter, regardless of mains power.
* If operated remotely or robotically, make sure that the roof/shutter will close itself upon mains loss or communication loss.
* Avoid any observatory design that requires the telescope to be in a certain position before the roof/shutter can be safely closed.
3. Observatories are (dynamic) machines, not (static) buildings.
* Choose fastening systems based on movement, shear, vibration, unexpected vector forces, corrosion and wear factors.
* Stainless steel machine and wood screws and Nylock nuts are your friend. Nails generally are not.
* Motor soft start modules can really extend the life of moving parts and guideways.
* The less moving parts, generally the better.
4. Observatory designs with 2D and 3D curves and arcs are considerably more difficult to construct from basic residential building materials.

Of course this list could go on for another couple of pages but these seem to me to be some of the issues that are the most often overlooked.

I hope this helps.

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yeah, i agree with erickson's list of considerations. and i'd suggest they lead to one conclusion. once you plug in all the thermal and operation issues, a dome or anything that rotates simply doesn't make sense without the single overriding criterion of thermal shelter in extremely cold conditions.

yes, domes or modified cylinders are used on the "big boy" observatories. but part of that is an engineering solution for a really big mobile structure.

i can't look at the models here without feeling that the modified cylinder is fundamentally an *esthetic* and conceptual solution to the shelter problem in a small instrument observatory. and that usually means the practical operation and maintenance issues, not to mention the management of thermal discharge through the "chimney", are going to be more of a hassle than you anticipate.

whatever you do, good luck.

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I like your second link...

Here is a simple solution for the track... Using an octagon of 2X12 or similar pieces, you can inscribe a circular track.... Instead of trying to make a perfectly circular piece.

I would use two courses rotated a bit so that their seams are not inline - to give additional strength.. Then put rollers on the bottom of the octagon shaped "cylinder" to rotate it...

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