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building an observatory dome- worth it?

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#26 MitchAlsup

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Posted 08 February 2020 - 01:28 PM

I built a 15 foot dome from scratch, took me 2 1/2 years working 20-30 hours a week almost non-stop.

 

Yes it was worth it!

Yes I would do it over again!

 

http://skychariot.co...nstruction.html

Why purple ?



#27 davidc135

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Posted 08 February 2020 - 01:57 PM

The plain garden shed or Pierre's fold over shelter would offer the easiest access to a number of users. Couldn't a temporary fabric shelter be rigged up against the wind?  David



#28 mark77

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Posted 08 February 2020 - 02:51 PM

Ventilating a dome so that hot air doesn't stream out the slit and into the telescope light path when the dome is populated by a number of people can be a significant issue for large domes.

I agree with this completely, I solved it by using attic vent fans.  I have 2 mounted in the dome itself but they are blocked by the slit door if it is all the way open.  They are used for air flow during the day.

 

I have a 3rd at the back of the 2nd floor where the dome is.  I put some ribbon hanging from the slit to determine air flow.  The one fan made significant air flow down through the slit and out the back.

 

https://www.homedepo...-EGV5/205924915



#29 mark77

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Posted 08 February 2020 - 02:58 PM

Why purple ?

Well, its really a long story but it is my my wife's favorite color (and now mine ).  A dome needs to be dark if possible.  I wanted the upper part to be dark as well.  However I did get  conflicting opinions on dark vs light on the inside of the dome.  It has worked out very well the way it is. Light enough when working in there and dark enough when observing.

 

You will however notice that all is balanced, the top is white with purple stripes and the bottom is purple with white stripes.

 

The long version of the story.  In 1997 I wanted to buy a Honda Goldwing Motorcycle.  We went to the dealer and test drove one, first me by myself and then with her on the back.  We were talking to the salesman and looking through the catalog.  They catalog showed that they had a purple one.  My wife said "If you get the purple one, you can get it now" We ordered it and had it in a week.  The rest, as they say, is history....


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#30 LarsMalmgren

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Posted 08 February 2020 - 03:21 PM

I don't remember. But all issues of Telescope Making are included with the Astronomy on CD/DVD. I assume Kalmbach would still be offering that, in some digital format?    Tom

 

~ click on ~ >>>

https://mysciencesho...oduct/dvd/15130

 

Note:  It appears to be NOT compatible with Windows 10 !



#31 bridgman

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Posted 08 February 2020 - 03:29 PM

Domes are awesome but the "need" depends a bit on the size of scope and type of mount.

 

For a 10" dob you have the advantage of being able to point the tube horizontally and then only needing a structure a couple of feet high to cover it up... I would think about a roll-off or even lift-off kind of observatory to start with.

 

A dome or a big low roll-off with fixed side walls would be nice if you have to deal with a lot of cold weather and snow, but that seems like observatory #2 to me rather than #1. You're going to need really low walls for a Dobsonian anyways, so a traditional observatory is less of a good fit.

 

If you do end up building a dome or a larger roll-off I still don't see much benefit in automation... to me automation becomes a really cool thing when you have a remotely controlled go-to mount and cameras on the scope.

 

Congrats on getting the scope nearly done.


Edited by bridgman, 08 February 2020 - 03:37 PM.

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#32 TOMDEY

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Posted 08 February 2020 - 04:34 PM

https://mysciencesho...oduct/dvd/15130

 

Note:  It appears to be NOT compatible with Windows 10 !

Sigh... that figures --- I think I tried running it on my laptop here and it --- wouldn't. And the older computer with old Win on it died. Pretty annoying. I still can't understand why these glamorous ~devices~ are not backward compatible ---not even marginally so. Must be planned obsolescence... intentionally making whatever we have loses support and even functionality after --- just a few years! Of course, if we mention that... the big digital companies tell us that WE are the idiots.    Tom



#33 BGRE

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Posted 08 February 2020 - 04:48 PM

I agree with this completely, I solved it by using attic vent fans.  I have 2 mounted in the dome itself but they are blocked by the slit door if it is all the way open.  They are used for air flow during the day.

 

I have a 3rd at the back of the 2nd floor where the dome is.  I put some ribbon hanging from the slit to determine air flow.  The one fan made significant air flow down through the slit and out the back.

 

https://www.homedepo...-EGV5/205924915

The dome ventilation schemes used at MMT (there is a paper on dome ventilation issues before the upgraded ventilation system ) and the VLT can be informative.

 

The heat produced by 20 or more people in a 5m dome with no ventilation apart from the slit noticeably affects the dome seeing.



#34 Kunama

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Posted 08 February 2020 - 05:11 PM

The dome ventilation schemes used at MMT (there is a paper on dome ventilation issues before the upgraded ventilation system ) and the VLT can be informative.

 

The heat produced by 20 or more people in a 5m dome with no ventilation apart from the slit noticeably affects the dome seeing.

Definitely noticeable at the eyepiece, we hold training sessions and observing nights in these domes and sometimes it is like looking over a warm house roof.....

I actually end up setting up outside for that very reason.....

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#35 TOMDEY

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Posted 08 February 2020 - 07:52 PM

All this talk about ~Observatory Domes~ brought to mind  a poem I composed about fifty years ago. I dug it out, dusted it off, and placed it here >>> , on Cloudy Nights!    Tom

 

https://www.cloudyni...poem-from-1959/



#36 speedster

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Posted 10 February 2020 - 03:33 PM

Howdy Gareth!

 

Best thing for school groups and outreach?  Lowell Observatory went through this and came up with the Giovale Open Deck Observatory.  A roll off building that you could scale down for your needs:

 

https://lowell.edu/g.../grand-opening/

 

I built a garden shed last year and the whole time I was thinking what a cinch it would be to turn it into a roll off building observatory.  One of these:

 

https://www.shedsfor...loor-p-438.html

 

Fab a simple perimeter steel tube frame on wheels, attach the building, open the doors, push the whole building off.  Open observing deck with room for multiple mounts and classroom/warm-room when the building is pushed back.  Put desk/computers/power in the back 5' of the building and then roll the building back until it hits the desk and your control area is always inside (and can be warm).



#37 laedco58

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Posted 13 February 2020 - 11:57 AM

F9C238F2-575C-41CD-B7BB-9598CD9EAFF5.jpeg

 

My Z-12 dob lives in this shed when not in use. It deploys in seconds with a two wheel hand truck.


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#38 Garyth64

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Posted 13 February 2020 - 01:12 PM

I built a 15 foot dome from scratch, took me 2 1/2 years working 20-30 hours a week almost non-stop.

 

Yes it was worth it!

Yes I would do it over again!

 

http://skychariot.co...nstruction.html

Impressive build!



#39 GarethBarry

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Posted 14 February 2020 - 08:23 AM

Guys- thank you so much for all of the replies! After reading them through multiple times, and having a meeting with the Headmaster,
- the headmaster is adamant that it should be in a dome- the 'wow' factor alone makes it worth while, also something interesting for the school boys to help build
- as a temporary measure, the dob will be housed horizontally in a small garden type shed that slides back.

Having said that- that Lowell observatory shed/observatory is really neat and clever....

The next step for the dob once finished will be converting to goto, probably using onstep.

Edited by GarethBarry, 14 February 2020 - 08:26 AM.


#40 Jeff Struve

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Posted 14 February 2020 - 09:19 AM

Guys- thank you so much for all of the replies! After reading them through multiple times, and having a meeting with the Headmaster,
- the headmaster is adamant that it should be in a dome- the 'wow' factor alone makes it worth while, also something interesting for the school boys to help build
- as a temporary measure, the dob will be housed horizontally in a small garden type shed that slides back.

Having said that- that Lowell observatory shed/observatory is really neat and clever....

The next step for the dob once finished will be converting to goto, probably using onstep.

Id like to see how well the dome works with a dob. Do you have an idea as to how tall the walls will be for the dob to see the horizon and how much headroom for people standing/sitting inside while using it?



#41 GarethBarry

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Posted 14 February 2020 - 12:46 PM

I am imagining the dome to be about 3 metres high/diameter, with about a foot high at the entrance/opening,or perhaps even less. The whole thing will be on a raised platform, with the 'balcony' being at least a metre extra around the dome, with a safety rail around it. The eyepice is a little under 2 metres high at the zenith. I would build the dome out of polystyrene and stuccoed or perhaps sprayed with a layer of truck bed liner (white obviously).

#42 macdonjh

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Posted 15 February 2020 - 10:37 AM

Gareth, after reading that you are building this for use by the kids at school I will second the others who have recommended a "Dob Shed" to store yor scope in. If you build a "full" observatory you will limit the number of people who can use your scope at any one time.

During the Mercury transit a couple of years ago I hosted something like 150 of my son's closest friends in a parking lot at his school. There is no way I could have had that many guests in my observatory.

For what I think your intended use is, a Dob Shed is least expensive AND most practical in my opinion.

#43 GarethBarry

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Posted 18 February 2020 - 09:50 AM

macdonjh- A very good point and this what you have articulated is a major concern. Perhaps the BEST solution is what has already been advocated, ie. an imaging scope in the dome and the dob gets wheeled out for visual use.



#44 appicloudy

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Posted 18 February 2020 - 07:55 PM

Hello Gareth

 

I built a 3m ( 10 foot ) aluminium dome 18 months ago, ( look in my photo folder if you want to see any photos ) as for was it worth it, yes without doubt. Would I do it again, yes but differently.

 

I had the ring laser cut along with the slot ribs, all the other ribs I rolled on a home made roller and welded into place, I sheeted the dome with .6mm ally sheet, these had an edge crimp to allow for the compound nature of the dome.

 

If I was to build another ( I won't ) I would have the base ring laser cut ( again in 2 halves then weld them together ) but instead of a ring I would have the outside cut in a series of straight cuts, at each intersection I would weld the rib, it could be riveted on, the ribs would also be cut into a series of straight sections, each with a change in angle to the ones next to it, so the rib would end up with a 90 degree curve in straights instead of one continuous roll. for the outer skin I would then cut the sheet sections into trapezoid shapes, put a small fold on each side and rivet into place.

 

The big problem with most dome builds seems to be water proofing, any plywood domes I have seen have a fiberglass tape applied to the join, I am a house builder by trade and that is a sure fire way of having a leak in the future. I expect my dome to outlast me with little or no maintenance.

 

The downside most people would say is welding the aluminium, I have welded steel for 40+ years and whilst welding ally IS different it isn't  that hard. After thinking of a better way to build an ally dome, the only welding really needing to be done is the two halves of the base ring, I'm sure most people could work out how to get that done.

 

BTW, mine took about 3 months to build the dome and another 4 months to build the obs and have the dome lifted into place.

 

I haven't done much work in the dome, I bought a Celestron CGX mount, so far it has been back to the suppler 3 times and the importer once, I may be fixed but I haven't had time to test it, bushfires bad seeing, and illness, hopefully soon, the times I have used it, it has been great to walk to the obs, turn the gear on and be up and running in several minutes, even on cold windy nights the dome stops most of the wind, warmer for me and no moving the telescope.

 

Dive in and build it, you won't regret it.

 

Ed


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#45 mark77

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Posted 18 February 2020 - 08:03 PM

Ed

 

Very nice build, almost identical design as mine but I used wood ribs. I really like your bending machine.  I looked into that but did not have access to one and a new one was way too expensicve.

 

Mine is 15 feet diameter and took 2  1/2 years.

 

I was just thinking earlier tonight that I would like to see more dome builds on this forum.

 

Do you have leaks, I do... ;(


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#46 appicloudy

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Posted Yesterday, 08:33 PM

Hello Mark

 

I was very lucky in that I was able to source bearings for both the ring roller and the small hand held roller very cheaply, FYI, I think the bearings for the ring roller were less than AU$10.00 each, I have a lathe so I was able to build the tools I needed to build the dome.

 

The reason I was thinking about alternative construction was so that most people on CN could build an ally dome, really that is doable if the dome was built the way I described ( or tried to ) earlier, yes it would be easier if the ribs  could be cut and tig'd but they could also just as reliable be cut and a gusset rivetted over the cut. The sheet cladding could be bent over the edge of a bench - it would only need a few degrees of bend.

 

Even the bottom ring could be joined with countersunk bolts, I have my wheels in the top of the support structure that supports the dome, but if the rollers were in the dome, you wouldn't even need countersunk bolts. So the dome could be built with no ally welding at all.

 

I don't have any leaks in the skin of the dome, I think this is due to each of the external cladding sections finishing on top of and over the section lower down the dome, this is the great strength of metal clad domes and the great weakness of plywood clad domes, for metal ones to leak the cladding needs to be holed, for plywood clad ones all it needs is for the fiberglass tape or whatever is used to crack or degrade and water will find a way in between the plywood cladding.

 

I did have a leak in the slot cover, mine is in halves and to keep the slot as wide as possible, I only allowed for a 50mm ( 2" ) lap when they closed, I was able to fix that by installing a section of cladding that was on the side that went under the original cover. This was set with enough clearance that the original cover still covered but was in turn covered by the new section. I rolled a very slight lip on the original section so any water would tend to run down the cover sheet rather than across it. I did that with in 6 weeks of installing the dome and in that time it hasn't leak at all.

 

If my explanation is a little fuzzy let me know and I'll take some photos, it was an easy fix to do, it may stop your leaks for the loss of a little of the opening slot width.

 

Ed



#47 mark77

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Posted Yesterday, 09:00 PM

Ed

 

My skin is aluminum with horizontal overlap, then LOTS of caulk followed by a 4 inch wide aluminum plate over the seam. I STILL have a couple of leaks, especially bad when the wind is blowing, but its more directional and I have not figured out which direction.

 

I also have a lathe and milling machine, but I found the idea of the wood ribs on the internet, perfected the making of the ribs by making  a jig to cut them and a "round table" as a jig to glue them together.  Time consuming but went very well.

 

For wheels, I just use 400 pound dolly wheels from Tractor Supply upside down for the plywood ring to ride on.  Works well.

 

I looked at your pictures in your gallery.  I would like to see some pictures of the completed dome/building.

 

Good luck with it

 

Mark



#48 appicloudy

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Posted Yesterday, 11:33 PM

Hello Mark

 

No problem, give me a day to two and I'll put some in my folder, I'll let you know.

 

Ed




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