I built an observatory a couple of years ago, but when I got into solar observing I quickly discovered that it wasn't ideal. Daytime observing can be very subject to bad seeing conditions produced by heat rising off of sun-warmed surfaces. The outside of my observatory is rendered and produces significant heat plumes when the sun is out. Viewing over a paved surface (even some distance away) can be equally disadvantageous.
So I decided to construct a permanent pier in the garden which would offer full east-to-west viewing over nothing but grass. I posted some pictures on CloudyNights, which stirred up some interest from another quarter: evidently some folks can't build full observatories because of local planning restrictions or neighborhood covenants. This approach might also suit individuals in those situations.
I live in a listed Georgian building, which required a sympathetic solution. A bare concrete pier formed with Sonotube or a length of Wavin pipe wasn't going to do. My solution came in the form of a "stone-effect" classical column, which is a hollow fiberglass casting. The first order of business was to cut a hole in the top and bottom so that it could be filled with concrete.
I acquired an armilary sphere from the same source as the column. It will go on the column when it's not in use.
[Ed: it's been pointed out that a removable sundial would also work -- and in fact I think it would be much easier to mount. In my case, though, I already had a sundial elsewhere in the garden, and my wife and I thought something a bit different would provide more interest.]
For stability, the column will stand on top of a 60cm cube of concrete sunk into the ground. The last indoor task was to construct a re-inforcing bar cage to provide strength in tension. The squares of plywood are just to align the cage until the concrete is poured -- they will not form part of the finished structure.
A bit of digging later and I had a 60cm x 60cm x 75cm hole in the ground. It was dug 15cm deeper than the concrete footer will be to leave room on top to replace the sod.
After about 30cm of concrete was poured, the re-inforcing bar cage was lowered into the hole.
When the foundation was complete, a bit of framing was added to cover the 15cm between the top of the foundation and the bottom of the column. This will allow the sod to be replaced once the form is removed.
The column then went on top and was filled with a slightly wetter mix. A 3x2 timber was used to tamp down the concrete as we filled in order to remove any voids. (The frame turned out to be a bit out-of-square, but it won't matter as it will be removed after the concrete has set.)
I left the concrete for a week to cure up nice and hard. Concrete tends to shrink a bit as it cures, and the wetter the mix the more it does so. Since we used a somewhat wetter mix in the column (to reduce the chance of voids), there was several millimeters of shrinkage.
The mounting ring for my mount is about centered on the fiberglass/concrete boundary, so I decided to add some Isopon so that it would be supported over its entire width. Rather than try and trowel (or sand) the Isopon flat, I placed wax paper over it and lowered the mounting ring down on it with a bit of force and then left it to set.
After a week of rain I was back at it: the top was drilled for 3 no. 14mm concrete anchors with 8mm stainless steel cap screws.
I used an angle grinder and a hacksaw to remove the bottom two rings of the armilary sphere, and after a bit of grinding the third ring up fit nicely in the Astro-Physics mounting ring.
That's pretty much it. The result is a nice, decorative feature when not in use:
A very stable platform for solar viewing:
(My solar setup consists of an Astro-Physics 400QMD mount carrying a Tele Vue Pronto with a 70mm Solarscope h-alpha etalon and 20mm blocking filter. The Pronto is run at f/23 with the help of a Barlow and an OCS in the binoviewer.)