[Atmob-club] observatory design question

[Mario Motta]

Hi George,

   I do not see how a rooftop can be stable enough without a pier. To
stabilize a large flat roof is a major undertaking, not easily done, likely
impossible, but I am no engineer. If you went the roof route, would need a
pier of some kind, then... would not be able to have a large area for
multiple scopes, so... back to a dome. You will not be able to keep objects
steady with many kids moving about otherwise, loose the advantage of a
rolloff. Also, most schools may have a liability problem unless you put a
cage around this on the roof to contain them.
I think you are better off if you keep it on the ground. If you do want the
rooftop, do a pier and a dome.

Mario Motta

On Jan 15, 2008 11:27 AM, George Roberts <gr at gr5.org> wrote:

>       I'm still trying to get a small observatory built for the local high
> school - hopefully a rolloff roof design in a field.  However, the whole
> high school will be rebuilt in about 3 years and this would be an
> opportunity to put an observatory on the roof.  There's a much better view
> from there.  Access would be easier to control, and getting access to
> electricity, internet would be easier.  However there would be other issues.
>
> One of the goals would be to be able to have occasional star parties at
> night - invite the whole town or invite a class of students.  So we would
> need to be able to host up to 25 or hopefully even 40 people (limiting to 40
> should be fine).  So we would need deck space for "open observing".  So I
> would still favor a roll-off roof design even on an existing 3rd story roof
> (strange).
>
> I'm sure you have comments about this and please do, but my main question
> is - in a normal modernly constructed steel building - how stable will the
> roof be if we mount the telescope right on the roof with no separate pier
> going down through all the floors into the bedrock (like they do at the clay
> center/southfield/dexter school)?  With 25 people horseing around and
> walking around will that make the view of the moon vibrate annoyingly?  Or
> are modern steel (and concrete?) buildings so heavy and strong and stiff
> that it will only be a minor problem.  And how about when there are only 3
> people sitting down calmly observing (which should be much more often)?  At
> night when the school is relatively empty and quiet?  Also what about when
> it is more crowded I envision a second or even third telescope setup on
> tripod on the roof?  I imagine an isolated rectangle of decking so that the
> tripod isn't resting on the same piece of wood as the people.  Or maybe it
> will be tar/gravel style roof with no decking.  Has anyone actually tried
> this?
>
> I know Harvard has that telescope on the roof and lots of people can mill
> around outside the dome on the roof and look at the stars.  Do they ever
> setup a second telescope on a tripod out on the roof?  Does the view jiggle
> at all?
>
> - George Roberts
>
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