[Atmob-discuss] observatory dome versus roll-off - looking for advice

[Mario Motta]

Hi George,

  As you know I stronly favor domes, so my advice might seem unusual, but
clearly not biased. For your school project a roll off makes the most sense.
first, buying a small 10 foot dome would be a major error. You will only fit
a few students at a time, could not have a group viewing without lots of ina
nd out activity. Small domes only make sense for remote observing or
individual observers.
A large dome bought would be prohibitively expensive for your budget, and
take some skill to build properly from scratch.  Still have problem of large
crowds in the dome.
A roll off allows best use., most students have never seen the sky well, let
alone view through a scope. this allows general sky viewing, allows large
classroom size crowds in the viewing area and not allow a buildup of heat
ruining observing. For wind, place barriers than can be raised on either
side.
Personal viewing, I strongly prefer a dome.
My thoughts,
Mario Motta


On 12/5/07, George Roberts <gr at gr5.org> wrote:
>
> My local High School started an Astronomy club (cool!) as I've mentioned
> earlier.  And now they want to build an observatory.  Currently the
> budget is $3k for observatory materials and $3k for telescope + camera,
> accessories etc.  We plan to get a 10 inch cassegrain.  We have a
> funding source (and can probably get more $ if we have to) and I'm
> working on getting permission for a location but I wanted to ask about
> observatory designs.  The Industrial Technology teacher is an
> experienced, licensed carpenter and wants to have his students build it
> over many months inside the H.S. Garage (lots of space and huge garage
> doors) and then final assembly out on the fields.  So I have free labor
> and some expertise.  The extra labor to make geodesic isn't an issue.
> The whole thing would be designed in their cad software down to every
> detail - different students could concentrate on different parts of the
> design.
>
> My question is about various designs.  We have looked at dome versions
> and roll-off versions.  I have always leaned to roll off.  It seems to
> me roll-off is simpler but the IT teacher thinks a geodesic dome would
> be better.   I guess he likes the idea of making a zillion triangles.
> So can some of you please give me opinions and ideas as to both methods?
>
> Some thoughts:
> Dome blocks the wind which is a big bonus.  I've heard about
> condensation problems as dew forms inside and drips down if it is a thin
> dome.  Explora dome makes a beautiful one piece polyethylene dome for
> $1100 shipped (8 foot diameter) (google explora dome to see it).
>
> Roll-off has advantage of seeing the sky with your eyes and not just the
> telescope.  Doesn't need cooling fans.  You don't need to have everyone
> duck under the doorway to get in and out (once the roof is off).  Easier
> to build maybe because no curves?
>
> In either case we would have concrete footings, a concrete pier
> (separate from floor vibrations) and the IT class would make a wedge out
> of thick steel plates (they love desinging this kind of stuff).  Maybe I
> can get the IT instructor to come visit the club's roll off plus
> someone's dome.
>
> - George Roberts
> http://gr5.org
>
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