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Equipment Discussions >> Observatories

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Gastrol
Pooh-Bah


Reged: 11/04/11

Loc: los angeles
Re: Why not a cylindrical observatory? new [Re: Goodchild]
      #5054284 - 02/03/12 10:52 PM Attachment (46 downloads)

Quote:

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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kiwisailor
Pooh-Bah


Reged: 01/07/04

Loc: Lyttelton, New Zealand
Re: Why not a cylindrical observatory? new [Re: Gastrol]
      #5054301 - 02/03/12 11:02 PM

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

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dobsoscope
sage
*****

Reged: 05/24/06

Re: Why not a cylindrical observatory? new [Re: Escher]
      #5054536 - 02/04/12 03:12 AM

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

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csa/montana
Den Mama
*****

Reged: 05/14/05

Loc: montana
Re: Why not a cylindrical observatory? new [Re: Gastrol]
      #5054670 - 02/04/12 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.

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Christopher EricksonModerator
Carpal Tunnel
*****

Reged: 05/08/06

Loc: Waikoloa Village, Hawaii
Re: Why not a cylindrical observatory? new [Re: BPO]
      #5055232 - 02/04/12 02:22 PM

Quote:

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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BPO
sage


Reged: 02/23/10

Loc: South Island, NZ
Re: Why not a cylindrical observatory? *DELETED* new [Re: Christopher Erickson]
      #5055668 - 02/04/12 07:33 PM

Post deleted by BPO

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BPO
sage


Reged: 02/23/10

Loc: South Island, NZ
Re: Why not a cylindrical observatory? new [Re: BPO]
      #5055712 - 02/04/12 07:59 PM

Unfortunately I've only been able to locate the following paper:

Some Airflow Properties of Telescope Enclosures Estimated from Water-Tunnel Tests

A search of Google should turn up others.


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Christopher EricksonModerator
Carpal Tunnel
*****

Reged: 05/08/06

Loc: Waikoloa Village, Hawaii
Re: Why not a cylindrical observatory? new [Re: BPO]
      #5055859 - 02/04/12 09:41 PM

Here is a better copy of the referenced document:

http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1991PASP..103..597A&defaultprint=YES&filetype=.pdf

FWIW, it is a controversial document that has not been universally accepted.

There have been many professional observatories planned and built since that document was published that have not accepted their conclusions. Note that the TMT and the ELT are both being designed as hemispherical domes and not as cylinders.


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BPO
sage


Reged: 02/23/10

Loc: South Island, NZ
Re: Why not a cylindrical observatory? new [Re: Christopher Erickson]
      #5056068 - 02/05/12 12:01 AM

There are several that have been built (or are in the planning stages) since publication that do utilise cylindrical or semi-cylindrical enclosures, or propose to do so.

It's not a cut-and-dried issue.

To my knowledge, ESO et al have no regrets.


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Hilmi
Post Laureate
*****

Reged: 03/07/10

Loc: Muscat, Sultanate of Oman
Re: Why not a cylindrical observatory? new [Re: BPO]
      #5056141 - 02/05/12 12:57 AM

My 2cent worth, If you're skills or money allow you to build a cylinder and not a hemisphere, then it's good to have a cylinder vs. not having an observatory

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Christopher EricksonModerator
Carpal Tunnel
*****

Reged: 05/08/06

Loc: Waikoloa Village, Hawaii
Re: Why not a cylindrical observatory? new [Re: Hilmi]
      #5056209 - 02/05/12 04:49 AM

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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nytecam
Postmaster


Reged: 08/20/05

Loc: London UK
Re: Why not a cylindrical observatory? new [Re: Escher]
      #5056279 - 02/05/12 06:20 AM

Quote:

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?


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

Quote:

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.


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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skoop
sage


Reged: 03/13/10

Loc: 59° N
Re: Why not a cylindrical observatory? new [Re: Christopher Erickson]
      #5056287 - 02/05/12 06:34 AM

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.

Quote:

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.




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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Christopher EricksonModerator
Carpal Tunnel
*****

Reged: 05/08/06

Loc: Waikoloa Village, Hawaii
Re: Why not a cylindrical observatory? new [Re: skoop]
      #5056950 - 02/05/12 01:53 PM

Quote:

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.

Quote:

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.




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




LOL!

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


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BPO
sage


Reged: 02/23/10

Loc: South Island, NZ
Re: Why not a cylindrical observatory? new [Re: Christopher Erickson]
      #5057404 - 02/05/12 07:29 PM

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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Christopher EricksonModerator
Carpal Tunnel
*****

Reged: 05/08/06

Loc: Waikoloa Village, Hawaii
Re: Why not a cylindrical observatory? new [Re: BPO]
      #5057466 - 02/05/12 08:23 PM

Quote:

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.




Being part of a hobby is beside the point.

The point I was trying to make is that when it comes to observatory reliability and design, it is most productive to view the observatory as a machine and not as a building. The differences may seem subtle but from an engineering perspective they can be significant. By definition buildings are static. Machines are dynamic.

I hope this helps.


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BPO
sage


Reged: 02/23/10

Loc: South Island, NZ
Re: Why not a cylindrical observatory? new [Re: Christopher Erickson]
      #5057486 - 02/05/12 08:34 PM

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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Christopher EricksonModerator
Carpal Tunnel
*****

Reged: 05/08/06

Loc: Waikoloa Village, Hawaii
Re: Why not a cylindrical observatory? new [Re: BPO]
      #5057501 - 02/05/12 08:47 PM

Quote:

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.




The professional observatories referenced all have intelligent, computer-controlled air flow shutters. Unless the amateur duplicates that feature, a direct comparison would be of limited value.


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BPO
sage


Reged: 02/23/10

Loc: South Island, NZ
Re: Why not a cylindrical observatory? new [Re: Christopher Erickson]
      #5057581 - 02/05/12 10:00 PM

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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Christopher EricksonModerator
Carpal Tunnel
*****

Reged: 05/08/06

Loc: Waikoloa Village, Hawaii
Re: Why not a cylindrical observatory? [Re: BPO]
      #5057604 - 02/05/12 10:17 PM

Quote:

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.




I think that you have it exactly upside-down.

At any rate, let's agree to disagree and let it drop.


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