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Why not a cylindrical observatory?

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#1 Escher

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Posted 03 February 2012 - 10:19 AM

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?

#2 zawijava

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Posted 03 February 2012 - 10:27 AM

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?


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

#3 Escher

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Posted 03 February 2012 - 10:31 AM

working on it... ;)

#4 dobsoscope

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Posted 03 February 2012 - 10:33 AM

i guess you're referring to something like this?

http://www.rainydaym...ervatoryBig.jpg

#5 dobsoscope

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Posted 03 February 2012 - 10:36 AM

http://astroprofspag...a00065sites.jpg

#6 MANDII

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Posted 03 February 2012 - 10:43 AM

yap ! this is a good question to ask about . Why not cylindrical ? and why not triangular ? Square ? I think any shape of oject can be rotated once it's put on a round track . You know there is a plate above the rotational track. And the dome of any shape can be mounted on this plate to achieve it's rotational view in 360 degree . So , firstly the rotating view problem is solved by the track,not by the shape of a dome . Then come th e the second question , it should be how big the view that this shape can obtained for a telsceope . 3rd question is how rigid /sturdy this shape can have when it is against the strong wind . 4thly how big this shape can provide the room among same amount of material being used . 5thly how much ennoying street light can be blocked by a certain shape of dome .

Among all factors , people think the spherical dome is the best shape , not the trainagula , cylindrical or others . Of course , that depands on your own needs .

#7 Escher

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Posted 03 February 2012 - 10:44 AM

Yup... but much smaller ;)

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#8 dobsoscope

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Posted 03 February 2012 - 10:45 AM

There is always the headache in making the transition from a whatever shape 'dome' to a circular track.

#9 MANDII

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Posted 03 February 2012 - 10:55 AM

well once we are going to build a Obs , headache cannot be avoided . All we need is just taking some useful drugs . :grin: And here I am just talking in more generally , and let us think more about the question of 'SHAPE" , specific technical problem , should be specificly seeing to it .

#10 Escher

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Posted 03 February 2012 - 11:03 AM

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

#11 zawijava

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Posted 03 February 2012 - 11:20 AM

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


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

#12 dobsoscope

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Posted 03 February 2012 - 11:21 AM

how about these

http://www.inhabitat...ds/kielder1.jpg
http://stargazerslou...hapter-4-a.html
http://www.google.co...kDbOM4gTr6a22Dg

#13 Escher

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Posted 03 February 2012 - 11:24 AM

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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#14 Escher

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Posted 03 February 2012 - 11:31 AM

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


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


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..

#15 StarWrangler

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Posted 03 February 2012 - 12:00 PM

What about the old Lowell Observatory
http://en.wikipedia....ell_Observatory

Alan O.

#16 Gastrol

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Posted 03 February 2012 - 12:28 PM

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

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#17 Christopher Erickson

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Posted 03 February 2012 - 12:34 PM

Historically the most important reason for building a dome is for wind management. It theoretically provides the best air flow over the observatory for minimizing wind forces on the telescope itself and for smooth heat stripping (rapid thermal equalization).

The shape of the ground and "ground scatter" (other objects) under and around an observatory can also greatly influence that air flow. The Subaru observatory here in Hawaii is cylindrical because after extensive wind tunnel tests, they felt that design (combined with an elaborate series of wind shutters) was the best design for handling the way the wind flowed over and around their chosen location at the summit of Mauna Kea. Possibly the most important feature of the Subaru Observatory is the fact that they open up specific pairs of wind shutters that allow wind to flow under the telescope and around the mount as part of their wind energy mitigation.

In general I would say that cylindrical observatories will not be as good as hemispherical domes for wind management for amateur observatories. And the nuisance of dealing with a multitude of curves and arcs in construction mostly remain.

One final note is that dome shutters that pull up and over are best for wind management. Split shutters that open laterally create their own wind turbulence and vibration problems.

#18 BPO

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Posted 03 February 2012 - 03:39 PM

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.)

#19 Escher

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Posted 03 February 2012 - 03:45 PM

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


I like this a lot... :bow:

#20 Goodchild

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Posted 03 February 2012 - 10:46 PM

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

#21 Gastrol

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Posted 03 February 2012 - 10:52 PM

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

Oops, I left out a line in the sketch above the door which divides the top and bottom half of the structure. The bottom half is stationary, top half rotates.
Here's the revised sketch.

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#22 kiwisailor

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Posted 03 February 2012 - 11:02 PM

Patrick Moore's Observatory was/is cylindrical- images here

#23 dobsoscope

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Posted 04 February 2012 - 03:12 AM

and how would you seal between both octagons to prevent entrance of dust/insects/wind etc. inside the observatory?

#24 csa/montana

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Posted 04 February 2012 - 08:37 AM

With that flat opening front; looks like it would collect snow & ice on it, in the colder climates; plus vulnerable to leaking. :question:

#25 Christopher Erickson

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Posted 04 February 2012 - 02:22 PM

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.)


I would think that this greatly depends if it is combined with elaborate wind (air flow) shutters under intelligent computer control that is also monitoring wind direction, speed, particulates, humidity and turbidity.

For observatories without wind shutters, any jutting 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. Depending on the effectiveness of the pier isolation, some of this "confused" energy can couple to the telescope mount and then on to the optics.

Also, rapid changes in air pressure in the observatory caused by turbulent air currents can directly couple to the optics of closed-tube telescopes (most refractors and most compound reflectors.) This can create interesting focus behavior in most commercial SCT's.

I hope this helps.






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