Any thoughts on an acrylic dome for an obsy?

[Breakintheclouds]

Now my pier is in place, I've spent months considering all sorts of ideas for an observatory. A roll-off roof isn't feasible for me thanks to space and the need to block a neighbour's bedroom lights, so it has to be some sort of dome.

I must have read a hundred descriptions of people making domes, but a lot of approaches seem a bit daunting. I'd almost settled on the geodesic dome approach, when I found there are various manufacturers selling acrylic domes in suitable sizes for not *that* much money.

Mine is going to be a very small obsy, only about 1.8m square at the base. And the dome can in principle be this size or slightly smaller - I calculate that even at around 1.5m it would allow a view of all the available sky. So does anybody have any thoughts on my using a dome from one of these places, painted, with a slot cut in it?

Stock Domes from acrylic, to your Specification or from our rage of acrylic stock domes.

Clear Acrylic & Plastic Domes, including Teedy domes, dishes and visidomes

Acrylic Domes

Acrylic Domes & Acrylic Hemisphere - ATL

[Rusty Strings]

Looks, in principle, like a good idea. I wonder what long term exposure to sunlight would do to the acrylic?

[lguise]

This sounds an interesting idea. I see the second company listed can make them up to 2.2m. The greatest problem will be making the shutter open and close easily and getting it weather tight. Any thoughts on this?

Linton

[MrJulius]

If the dome is transparent or opaque you might get problems with stray light.

Also would not the sun make the color of the plastic and paint fade?

[yesyes]

The greatest problem will be making the shutter open and close easily and getting it weather tight.

My thoughts exactly. I'm sure it can be done but haven't got a solution yet .. ;-)

[yesyes]

If the dome is transparent or opaque you might get problems with stray light.

Also would not the sun make the color of the plastic and paint fade?

Sun? What sun?

The stray light wouldn't be any worse that with a roll-off roof.

The acrylic would probably change colour and transparency (if it is transparent to begin with) over time. But since you won't be observing *through* the acrylic, this effect should just be cosmetic.

[Breakintheclouds]

Thanks for the thoughts, everybody. I've not yet contacted the manufacturers (will do that soon), but I think some of these places can make domes in a dark-coloured acrylic, which might help a lot. Whether coloured or not, I think I'd paint the exterior white with some sort of outdoor paint for added protection.

At the moment I'm thinking this: if I get a hemispherical dome with a flange, I could mount upside-down casters on the top of the observatory base and run the down around on these really easily. The two challenges, then, are (a) stopping the dome flying, or being lifted, off; and ( stopping rain blowing underneath. But both of these feel like things that could be solved quite easily, and in a suitably low-tech way.

I'll update when I have news on the domes!

[yesyes]

if the dome has a nice round flange and even thickness, you could have pairs of castors, one below and one above the flange with the flange moving between the wheels, if you see what I mean.

[Breakintheclouds]

Ah, yes - castors ABOVE the flange as well to sandwich it. Good idea!

[Doc]

How about a dome inside a dome. Both with a 60° cut out. The outer and inner will need to rotate so to line the cut outs together for an open view, then rotate the inner one to close the opening.

All you need then is some waterproofing mechanism on the outer one.

[Breakintheclouds]

Doc - that's a REALLY smart idea! Alas, I worry it'd be getting into the realms of too expensive. It's still going to be into the hundreds of pounds for a big dome and so two would be too costly. However, having said that, you have got me thinking now. If I buy a nicely manufactured, smooth plastic dome, surely there'd be some way to take a mould of it. If I could find the right material, and mould a copy over the top, then this would fit perfectly and tightly, and would allow the rotating idea you describe.

Hmm... Any thoughts on material?

[Doc]

Cheers I'm full of good ideas.

[Wobbly Bob]

Those OCEAN domes look pretty robust.

[Breakintheclouds]

Bob - The aquarium domes should look robust: I called today and they want nearly £4k for one! A couple of the other companies had prices for domes not designed to hold tonnes of water nearer the £600 mark. I've got at least one more place to try which I hope might be even cheaper.

The thought of sawing a hole in a £600 dome is quite daunting.

[Astrokev]

Hmm... Any thoughts on material?

I'm not expert in it's use, but glassfibre would probably do the job nicely. I'm sure you could line the acrylic with a suitable release agent or material to prevent adhesion to the plastic.

Kevin

[r3i]

Bob - The aquarium domes should look robust: I called today and they want nearly £4k for one! A couple of the other companies had prices for domes not designed to hold tonnes of water nearer the £600 mark. I've got at least one more place to try which I hope might be even cheaper.

The thought of sawing a hole in a £600 dome is quite daunting.

£4k!!! - ouch!!!

If you're thinking towards some kind of clamshell design, and if it looks like the acrylic dome route is going to end up costing upwards of £1K, then maybe you could look into buying just the dome section of a SkyShed POD? Their site has the price of just the dome at $895. Altiar Astro are the UK distributors and I don't think they have the dome only option listed on their site but I'm sure they could get you a price. I visited their shop recently and they're a friendly and helpful bunch.

At least you'd avoid the anxiety of having to cut through the expensive acrylic!

[Doc]

£4k!!! - ouch!!!

If you're thinking towards some kind of clamshell design, and if it looks like the acrylic dome route is going to end up costing upwards of £1K, then maybe you could look into buying just the dome section of a SkyShed POD? Their site has the price of just the dome at $895. Altiar Astro are the UK distributors and I don't think they have the dome only option listed on their site but I'm sure they could get you a price. I visited their shop recently and they're a friendly and helpful bunch.

At least you'd avoid the anxiety of having to cut through the expensive acrylic!

This is the route I would go down as well.

[MartinB]

One thing you need to bare in mind with a small dome is the maximum aperture you are going to be able to achieve and the aperture of your scope. The problem comes when you are imaging near the meridian with the scope at it's maximum distance away from the north south axis of your mount. The aperture needs to accomodate distance between the outer edge of your scope on the east and west sides of mount, if that makes sense. It is actually a bigger probem with wide aperture SCTs than it is with Newtonians because of SCTs are further away from the dome opening but still can be an issue.

[yesyes]

If it's only space that's preventing you from building a roll-off roof obsy, you may also consider other alternatives, like this one:

http://stargazerslounge.com/diy-observatories/106749-rotating-roof-obsy-pics.html

[Wobbly Bob]

This is the route I would go down as well.

I went the whole hog and bought a Skyshed POD, brilliant.

[Breakintheclouds]

YesYes: Thanks for the link. However, it's not just space that's my issue: I also need protection from neighbours' lights, so a dome would be much better.

[yesyes]

Just toying with alternative ideas. ;-)

The rotating roof could be constructed in a way that it blocks the light from your neighbours when in the "open" position... Just a thought though .. ;-)

I myself would probably not go for a dome as it would be too obvious and suspicious when the neighbours look at your garden.

[Doc]

I went the whole hog and bought a Skyshed POD, brilliant.

Lovely Bob.

Has it got a docking bay for you 4x4

[Edi]

Now my pier is in place, I've spent months considering all sorts of ideas for an observatory. A roll-off roof isn't feasible for me thanks to space and the need to block a neighbour's bedroom lights, so it has to be some sort of dome.

I must have read a hundred descriptions of people making domes, but a lot of approaches seem a bit daunting. I'd almost settled on the geodesic dome approach, when I found there are various manufacturers selling acrylic domes in suitable sizes for not *that* much money.

Mine is going to be a very small obsy, only about 1.8m square at the base. And the dome can in principle be this size or slightly smaller - I calculate that even at around 1.5m it would allow a view of all the available sky. So does anybody have any thoughts on my using a dome from one of these places, painted, with a slot cut in it?

Stock Domes from acrylic, to your Specification or from our rage of acrylic stock domes.

Clear Acrylic & Plastic Domes, including Teedy domes, dishes and visidomes

Acrylic Domes

Acrylic Domes & Acrylic Hemisphere - ATL

plastics for you Stock Acrylic TEEDY Domes & Plastics Domes

[Edi]

YesYes: Thanks for the link. However, it's not just space that's my issue: I also need protection from neighbours' lights, so a dome would be much better.

plastics for you Stock Acrylic TEEDY Domes & Plastics Domes