I have a 24x24 foot building (barn roof) in my backyard which serves
as a garage...
I am into astronomy and because of trees etc the only good place to
"construct" an dome shaped observatory is to place it on top of the
The weight of the Fiber glass dome with a 6 foot 6 inch headroom in
the center is only 350 pounds (the walls dome itself)... which leads
me to think that I really could build a 8x8 platform on top of the
existing roof and erect the fiberglass dome...
Existing rafters are 2x6;s spaced 24 inches on center gable shaped .
I would not be removing any...just cutting a hole in the roof under
the dome so I can climb up a ladder to enter...
Seems to me that adding 350 pounds PLUS "me" and the Telescope and the
laptop on the roof would be possible..
What I do not know yet is how to mount a pier up there so that it
would be stable enough to hold the telescope stable ... First things
first... can the existing roof hold the weight....?
We need the roof-span, as well as the rafter size and spacing,
and the weight of the scope assembly. On the other hand, you're
talking about a concentrated load of around 500#, plus possibly
another person. I'd sister up the rafters in question anyway.
I would think it would "hold" the weight. the question is could you use a
telescope on such a platform. There will be a certain deflection to any such
arrangement. (jump up and down on the roof and you will notice it moves).
Any telescope I have used needs a solid non moving base for any decent
Exactly. any roof is WAY too bouncy for a telescope mount, and your roof is
very lightly built by roof standards, with only 2x6's on 24" centers. Look
around the web for home built scope articles, they all use large concrete
If the roof is the only suitable spot for viewing, you will need to add
something like vertical posts embedded in concrete and mount the platform on
top of them to isolate it from the building. Of course, then you give up space
in the garage due to the posts.
On 8-Nov-2005, snipped-for-privacy@SPAMwowway.com (DT) wrote:
You need to isolate the platform from the building so that the building
doesn't have to carry the high loads. It is also a good idea to isolate
the telescope pier from the platform. I know folks that have built a thick
pier for the telescope and separate columns to hold up the platform. The
platform, dome etc are not connected to the pier except through the
foundation/soil. The telescope pier should be well damped to avoid
If you're going to put up a fiberglass dome, you will eventually keep
adding telescopes and other gear. The weight adds up fast.
If you are going to go to that much trouble, I would caution against
actually building the dome on the existing building. Thermal effects
will mess up your seeing - better to build a stand-alone telescope
dome if you have the land.
Depends on the heavenly body at which you are gazing.
When I was in school, the grad students gimmicked up the world's 7th-largest
refracting telescope to depress below the horizon. "Why," you may ask?
A mere four miles away was a girls dorm....
And to think, nowadays there are web cams in many girls' dorm rooms.
$29.95 a month, charges discretely show up on your phone bill as
Must've been rough in the old days.
Here\'s some of my work:
Too much bounce. Any movement on the floor will transmit to the
telescope. Vibrations will make the scope almost unusable.
It has been done by making a "Very Solid" pier from the ground
up to the second floor. The pier would have to be something
as solid as a 16" concrete pile 15-20 ft into the ground.
The entire structure has to float free of the pier, not touching
it at all. The only thing on the pier is the telescope.
I used to be a member of an astro. group that had an observatory
on the second floor. The telescope, a C 14 was mounted as I
described, but as I recall the pier was at least 20" in diameter.
By the way, there can be no heat in the building below. Warm air
rising will interfere with seeing.
You may want to try the newsgroup sci.astro.amateur
Hello Bob, Others have brought up good points, which I myself wouldv'e
brought up to you also.
You make no mention of scope, mount, and if you've already purchased the
I'm an Amateur Astronomer myself in Southern NM, and a few years back,
when living in Chicago, I bought a 2 month old Celestron C-14 OTA from a
fella living about 100 miles south of Terre Haute, IN.
He sold the C-14 to upgrade to a more expensive 12" RCOS Cass.
He was using an AP1200GTO Mount, which I myself also used to own (just
sold mine) and it was on the second floor of his house. The pier went
through the observatory floor, through the first floor, through the
basement floor, and down to bedrock. No matter what he did, (Bracing,
etc on the lower floors) he still would get shake/vibrations, and had to
be extremely careful when imaging with his SBIG CCD Cam.
With his arrangement, he had constructed a rool off roof on his house,
instead of using a dome, as you wish to do. A roll off Section could
possibly be built lighter than the 350 lb Fiberglass Dome you propose,
and no doubt much much cheaper also.
As another mentioned, thermals will most likely torture you also. I can
recall this fella I mention needing to resort to AC in his observatory
to bring temps down.
I'm sorry to hear that you don't have too many options with the
surrounding trees in your area.
Hope you can solve your problems. Mark D.
On Tue, 8 Nov 2005 20:49:50 -0700, email@example.com (Mark D) wrote:
I honestly do think I could avoid most of the thermal effects
since the garage is unheated unkless I am out their playing with one
of the cars (another hobby ..)...but I think that I would have major
problems stablizing the scope .... I have to use vibration supression
pads under the tripod feet now...plus I use a electronic focus motor
because no matter how gentle I try to adjust the focus the scope rocks
and rolls so to speak...(using a Celestron Heavy Duty Tripod..which is
not up to the task...)
Just got the idea of mounting a dome on the roof to avoid the trees
that I planted 30-40 years ago...I can construct a small shed with a
roll off roof for a lot less money then purchasing a dome anyway...and
install a pier anchored solidily in concrete to mount the scope on .
Still will give up most of the Northern Sky but what the heck..
Even if it is unheated, the roof alone will pick up a lot of
heat from the sun. That heat will take quite a while to
dissipate and will ruin your seeing the whole time. This
problem will occur winter or summer, though in winter you
might see the roof cool off quicker. The skies are more
turbulant in winter anyway, so you just can't win!
Learn from others - you do not want to have a large roof
just below the level of your observatory.
I'm a farmer. If you are referring to an actual barn (some people
call anything except their house a barn), then I would not even worry
about putting 500 lbs up there. Heck, snow adds several tons to roofs
at times. I would however, run a few vertical posts under your dome
to the supports under the floor below just to add stability.
As far as using a telescope, I dont know anything about them. Listen
to the others on here.
On Tue, 08 Nov 2005 13:01:56 -0500, Bob G.
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