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#1 mlcolbert

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Posted 28 July 2008 - 05:24 PM

Yes, I know, most think, what the....???? But I want to run this idea past you guys to see what would be the potential problems or benefits.

Have a hole 2.5 metres deep by 5 metres diameter. Have the walls sealed, pier mounted in concrete etc. Optional dome to be placed on rails or slide off roof on rails across ground. Given that there is a clear horizon and that the pier would allow extension to ground level for the ota. Also, that there were no dangers of people or animals wandering into the area.

What do you think? Practical or otherwise?

michael

#2 Chris Schroeder

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Posted 28 July 2008 - 05:46 PM

I would be worried aboue too much mositure.

#3 csa/montana

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Posted 28 July 2008 - 05:58 PM

Also, that there were no dangers of people or animals wandering into the area.



How would you stop animals or people from wandering into the area, and perhaps an animal not suited to be good company joins you? :grin:

#4 Pedestal

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Posted 28 July 2008 - 05:59 PM

Whatcha gonna do when it rains....
h

#5 NeoDinian

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Posted 28 July 2008 - 07:46 PM

Whatcha gonna do when it rains....
h


It would become a Periscope... :)

#6 Snow dog

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Posted 28 July 2008 - 09:16 PM

I would say that rain would be an issue too. Not to mention if your in an area that gets lots of snow. Your observatory would become an igloo :lol:

#7 nytecam

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Posted 29 July 2008 - 02:19 AM

I'm amazed this suggestion pops up again so you should read the final chapter in Patrick Moore's book Small Astronomical Observatories by Springer - the "Carter Observatory that wasn't" :lol: In summary a man with identical ideas digs a massive hole by hand and take a short vacation to recover his strength. On his return the hole is full to the brim with ground water so he throws in a few goldfish and abandons the observatory project :bawling: PS:Might work in a desert ;)

#8 John Fitzgerald

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Posted 29 July 2008 - 07:03 AM

If it's a "walkout" on one side, it might work OK.

#9 mlcolbert

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Posted 29 July 2008 - 07:46 AM

thanks for the comments guys, so to reply;

1. John, yes a walk out or up stairs would obviously be the way to go. Not really seeing the idea of me jumping into and out of a hole that size. :)
2 re the concerns about rain, this is why I originally mentioned sealing the walls and of course the roll off roof or dome. If either are used then the rain or snow is not a problem. I was not suggesting an open hole with no cover.
3. animals other than amateur astronomers, now there's an interesting problem given that this would be located in a rural environment, obviously with fencing restraining the ordinary cattle / sheep :)) But as for the smaller ones, maybe the activity and some prerecorded sounds like predators would keep those away?

Any other problems that you could think of??

Thanks

michael

#10 Bob Antol

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Posted 29 July 2008 - 08:14 AM

Also, be sure to check out The Hartness House Observatory at http://www.hartnessh...-history.shtml.

#11 StarWrangler

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Posted 29 July 2008 - 08:30 AM

Check This Out,

http://tinyurl.com/63sasf


Alan

#12 John Fitzgerald

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Posted 29 July 2008 - 11:36 AM

My roll off is out in the wild. Animals don't bother it. There is no food or food smells in there, so no reason for them to care. I don't see animals as ever being a problem in a well built observatory.

#13 StarWrangler

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Posted 29 July 2008 - 12:59 PM

Mine is in my backyard but we get Coyotes and other animals,\



Alan

#14 mlcolbert

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Posted 29 July 2008 - 04:51 PM

Bob and Alan thanks for the link. Now that is extensive and also has the classic dampness problem. But wow! It gives one things to think about!

michael

#15 StarWrangler

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Posted 29 July 2008 - 04:54 PM

Hi michael ,

If I ever build another observatory I would have it attached to the house with a doorway from the house into the observatory,


Alan

#16 Dennis H.

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Posted 29 July 2008 - 07:04 PM

Use poured concrete walls that go at least 6-8" above the ground level, with a really good footer drain, I don't see why it can't be done.
I can see how it would be easier in certain locations more than others.

The neighbors might think you are building your own Titan II missle silo though! :bigshock: :bigshock:

#17 RobVG

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Posted 31 July 2008 - 10:43 PM

I think the idea of an underground observatory is pretty cool.

I got to wondering if you could bury a shipping/cargo container for the basic structure. You can buy a used 8'x20' container for about $1000 but it turns out they're not structural- the sides would have to be reinforced.

Then I found plastic storage tanks tanks for $875 which are 8' in diameter- good size for a dome. The walls are a little tall but you could build a false floor- good for running wires anyway. They come bigger but the cost goes up accordingly.

You'd have to cut the top off the tank maybe leaving a rim around the top edge for strength to keep it from buckling. You could pour a pier plug and a slab with anchor bolts for a metal pier.

You'd need to drill holes in the tank for the anchor bolts and find a good sealant, and paint some bulls-eye's on the slab to set the tank on and seal around the anchor bolts. If possible, a footing drain would be a good idea. :smirk:

Possible sealant source

#18 mlcolbert

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Posted 01 August 2008 - 07:01 AM

Rob, you'll have to keep us up to speed how you go when the building stage comes along!

michael

#19 DeanS

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Posted 01 August 2008 - 08:45 AM

Seeing gets better the higher off the ground you get. At ground level these effects are noticeable, particularly if you are already in a low place.

I get fog around the lower sections of my back yard and many times it stops right near the observatory and if I was ground level it would shut me down. Also the dew would be a major issue to deal with.

I would not want to do it unless that was my only choice due to building restrictions. Plus the cost will possibly be even more if you have to pour wall?

Good luck

#20 Bowmoreman

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Posted 01 August 2008 - 03:01 PM

Unless you have it in a really arid climate, you are going to have huge issues with humidity... There is no way to really avoid this.

the deeper your hole/walls, the colder it will naturally be (unless you simultaneously heat it)... this causes relative humidity to skyrocket. If you dehumidify, that heats it in the process...

Depending on how rapidly the air in the underground space is (or can be) exposed to outside airflows will determine if you will get so humid as to actually reach saturation and the resultant condensation - on every surface...

Even Super Insulating is not going to help you, because, unless you can super insulate AND also make it 100% airtight (versus outside air) - the outside air (warmer and therefore carrying higher moisture content) will get in and be exposed to the colder area below ground... and raise RH and/or condense...

And, you don't want to have a 100% airtight observatory anyways - defeats one of the main points - instant acclimation to ambient temp... You've got two conflicting requirements with such a design.

Here's a real world datapoint: I built a super insulated wine cellar in my 8' deep basement. It has R90+ insulation in the ceiling, and R68+ in the walls. Full vapor barrier. Exposed concrete floor inside (so has a heat "sink" at deep earth ambient temperature, which here in MA is around 55F).

In Winter, the air temperature stabilizes at a low of 57F, in Summer, it gradually peaks at a high of 63F; with gentle swings in fall and spring to/from those values...

The humidity varies from 80% in summer, to around 55% in winter. This is totally passive, and with COMPLETE vapor barrier (and double doors as well!).

Not a telescope friendly climate:

Too humid and NEVER at ambient to outside...

Sorry, I just don't think having the actual observatory be undergound makes any kind of sense...

It would only work if you had very highly regulated HVAC control of temperature and humidity, AND also had massive insulation...

Why bother??? Uber-expensive, fiddly, etc...

Sorry to "rain" on the idea parade...

Again, this only applies to areas that HAVE humidity and temperature swings... it might work out ok in Arizona, New Mexico, Nevada, Utah and other places similar...

clear enough skies

#21 andyschlei

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Posted 05 August 2008 - 06:41 PM

I'd echo Dean's comment on seeing. You want to be off the ground, most seeing problems are in the first 20 feet or so above ground.

#22 starquake

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Posted 15 September 2009 - 01:24 PM

Actually, I'm currently building an underground observatory. At least some part of it is underground (see pics: 1, 2, 3).

As you can see, the 4m diametre dome will be above the ground.

I've thinked over all possible problem sources, and decided to give it a go. The hole has a depth of about 1m with a diametre of 4m. I digged it by hand almost two years ago. I was examining its behaviour since, especially after big rains. But as this place is on top of our "hill" about 22m above the house, there's no sign of ground water even after weeks of continuous rain.

I've read many comments about seeing at ground levels, and realized that if I wanted the scope at a seeing-safe height, I either must use the top of our roof (then I have strong turbulences over the roof any night of the year, so it's not an option), or build such a tall building, that the loooooong pier would shake strongly very probably. The dome design however is good at keeping away wind turbulences from the scope, so it's still much better to have the scope in a dome than to have it standing on a tripod in the yard. I've also noticed that on the top of the hill there's only a minor sign of moisture even if down in the valley we have a fog, which is quite common throughout the year.

Btw, I'm building a horseshoe mount to be placed in the underground observatory (here's a pic), to give the scope even better stability than a normal pier.

Why underground then, you may ask? The answer is that I _think_ the scope mirror will stay closer to a thermal equilibrium state, because the ground around the mirror will keep a colder temperature inside the dome than what a normal domed observatory could provide. That is essential for me, because we often have days especially during the summer, when the temperature falls so rapidly during the night that the mirror just can't keep up with this rate, and fails to reach the equilibrium through the whole night.

Anyhow, I'll finish the walls this week and start to build the dome, so I'll be able to report the first impressions soon, if you're interested.

#23 csa/montana

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Posted 15 September 2009 - 01:38 PM

Thanks for sharing this very unique Observatory you are building! We definitely would appreciate following the building of this, as you progress.

#24 will w

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Posted 18 September 2009 - 08:20 PM

it can be done with proper planing and materals.has anyone thought about a tower?? like a fire tower,maybe not 90 ft in the air. it will work.

#25 AlienFirstClass

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Posted 19 September 2009 - 12:18 PM

Unless you have it in a really arid climate, you are going to have huge issues with humidity... There is no way to really avoid this.

the deeper your hole/walls, the colder it will naturally be (unless you simultaneously heat it)... this causes relative humidity to skyrocket. If you dehumidify, that heats it in the process...

Depending on how rapidly the air in the underground space is (or can be) exposed to outside airflows will determine if you will get so humid as to actually reach saturation and the resultant condensation - on every surface...

Even Super Insulating is not going to help you, because, unless you can super insulate AND also make it 100% airtight (versus outside air) - the outside air (warmer and therefore carrying higher moisture content) will get in and be exposed to the colder area below ground... and raise RH and/or condense...

And, you don't want to have a 100% airtight observatory anyways - defeats one of the main points - instant acclimation to ambient temp... You've got two conflicting requirements with such a design.

Here's a real world datapoint: I built a super insulated wine cellar in my 8' deep basement. It has R90+ insulation in the ceiling, and R68+ in the walls. Full vapor barrier. Exposed concrete floor inside (so has a heat "sink" at deep earth ambient temperature, which here in MA is around 55F).

In Winter, the air temperature stabilizes at a low of 57F, in Summer, it gradually peaks at a high of 63F; with gentle swings in fall and spring to/from those values...

The humidity varies from 80% in summer, to around 55% in winter. This is totally passive, and with COMPLETE vapor barrier (and double doors as well!).

Not a telescope friendly climate:

Too humid and NEVER at ambient to outside...

Sorry, I just don't think having the actual observatory be undergound makes any kind of sense...

It would only work if you had very highly regulated HVAC control of temperature and humidity, AND also had massive insulation...

Why bother??? Uber-expensive, fiddly, etc...

Sorry to "rain" on the idea parade...

Again, this only applies to areas that HAVE humidity and temperature swings... it might work out ok in Arizona, New Mexico, Nevada, Utah and other places similar...

clear enough skies


How do you handle the humidity in your cellar?






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