Observatory

Observatory

Sooner or later every astrophotographer gets tired of spending hours of dragging all equipment out of the house into the open, setting everything up, polar and drift aligning every night, only to discover that clouds have drifted in yet again and everything can be packed before it actually starts to rain…..

The solution is of course some kind of permanent housing for all the imaging equipment.

This section tells the story of how the observatory was planned, ordered, built, modified (and modified again) until it got its final state as it is in today (that is until the next modification).

Article index:

Clicking on a small thumbnail image from the right column below will open a separate window with a larger version.

Location

At the end of 2006, after 3 years of dragging equipment from and to the house, I took the decision to find a more permanent solution for my imaging equipment in the form of an observatory to be placed somewhere in the garden.

An observatory was going to be built in 2007 !

Ok, so we took the decision to build an observatory, now where in the garden are we going to put this thing ?

Well, this decision was taken quite easily, as there simply were not many options available.

There is a (very) large Ahorn in the neighbouring garden blocking the sight to the northwest (some of the branches of this tree can be seen in the small image in the top-left corner), the house blocks the southern sky and a line of trees blocks the northeastern sky to some extent.

The only viable option was to build an observatory in the right part and center of the garden in order to take full advantage of the eastern and southern sky.
The location was put forward as far as possible (just need Polaris in the northern sky), this enabled us to image the southern sky by overlooking the house by a larger amount of degrees.

Planning

After doing some extensive research over a couple of months, one of course needs to take a decision as to what kind of construction is going to be built. Will it be a dome or a roll-off roof observatory, should I modify an existing garden shed design, buy observatory construction plans or build one myself from scratch ?

Buying a dome was the first option which was dropped, most important reason was of course based on a cost point of view as a dome is the most expensive option available.

Besides this there is the limited opening through which to image, the limited size of the dome, at least if you do not want to construct an additional building next to the dome in order to increase total observatory space available. An other factor to consider is that having a dome, does a very good job at attracting unwanted visitors during the night as it is quite a conspicuous building to have in one’s garden. A modified shed does not immediately reveal it’s intended purpose and is therefore not likely to attract as much unwanted attention. (especially a remote site).

One of the other options was buying observatory plans, the problem with these plans were however that most of them were not specifically designed for the European market (non-metric dimensions!) and not all materials are available here. So this idea was dropped too.

Out of the 2 remaining options, building an entire observatory from scratch was also not really a favorite option, as pricewise it was cheaper to buy a complete shed and modify the construction than having to buy lots of wood of different dimensions and constructing it yourself. Besides, building a pre-fab shed is a matter of hours so you can concentrate on the modification on the afternoon of the same day you started putting the shed together, this is something you won’t be able to do when building from scratch.

So basically the ease of and time spent on construction as well as the total price were the most important factors in the decision making process of what type of observatory to build and ultimately choosing for the modification of a pre-fab garden shed.

Foundation & pier

Before starting to construct a pier, several issues need to be sorted out:

– What material should be used for encasing the concrete ?
– What should be the total height of the pier and what length should be put into the ground ?
– Which inner/outer diameter should be taken for the tube ?
– What should be the exact location of the pier inside the observatory ?

As Sonotube is most commonly used, it was of course the first choice of material to be used for encasing the pier when pouring concrete. There was however only one small problem, Sonotube is not available in the Netherlands !

I had to find another solution to the “Sonotube-problem” !
Luckily, what we do have are large PVC tubing. I found a store called Wildkamp, which actually sells PVC tubing from 32mm sizes up to a ridiculous 630mm diameter tubing.

As the base of the G-11 is rather large and in order to get a more or less correct spacing for the rods and bolts in a steel plate on which to place the G-11 (using attach the Meade Field tripod adapter) I decided to go for a 2m long, 250mm diameter tube for the pier. The 250mm diameter tube should provide enough concrete around the rods to have them enclosed in a proper way.

In order to get a sufficiently large base and still have enough pier height available inside the observatory, 70cm of the pier was placed into the ground, leaving 130cm of pier height for the observatory. As shown in the image to the right, part of the concrete base was put slightly (approx. 10cm) above the soil to further increase stability. Please note that the observatory floor should NOT rest on this base !

Now that we have got the material, height and dimensions figured out, the next issue which needs to be addressed is where exactly to put the pier ? – should it be put exactly in the center of the observatory or apply some kind of offset ?

As I do not have a clear view of the northern sky (I can see Polaris however), imaging in this part of the sky was not really an option. I decided to not put the pier at the center of the observatory but offset it towards the north.

An offset towards the northern part of the observatory would free up more space for other equipment in the observatory behind the mount and scope. Besides this, it also provides a larger imaging area in the southern sky, as the pier is further away from the southern observatory wall allowing me to image objects in the southern sky at a lower angle.

Once we have determined all of the above, it is time to fill the PVC tube with rebar and concrete.
As shown in the image above and to the left, the rebar was cut and bent into the correct dimensions and was welded together in order to get a more solid construction before pouring the concrete.

When using a rebar frame, remember to never allow the rebar to make contact with the soil, as this will cause corrosion of the rebar and will cause severe stability issues over time with the concrete base of the pier !

After pouring the concrete allow it to dry out for several weeks. Remember to fix the rods in the concrete in order to prevent any movement when the concrete is drying (I used a piece of multiplex wood cut to the correct dimensions to keep the rods fixed inside the concrete when drying – visible in the image to the right).

Building

After the pouring of the pier was done, the remaining base needed to be completed (= more conrete) before construction of the shed could actually begin.

The base of the shed consists of hollow concrete pre-fab blocks (see image of the pier above).
By using this type of concrete blocks, we can make sure that the floor of the shed is well above ground level providing additional ventilation and because the floor is not in contact with the soil it will decrease any potential issues with moisture. (when raising the floor above ground level some measures need to be taken however in order to prevent any unwanted visitors from crawling under the observatory floor).

As shown in the image to the right, more rods have been placed in the concrete of the base of the shed in order to attach the beams to the concrete base.
The rods have been bent into a “J” shape for additional hold in the concrete.

After the concrete hardened, it was time to build the shed and start modifications to a roll-off roof design.
Fortunately the weather decided to cooperate for a change on the day the pre-fab shed arrived (and for some strange reason also during the next couple of days) so building the shed could actually start as planned.

The first thing to do was to fix the “base beams” to the concrete blocks by using the rods that were placed in the concrete.

A large drill was used to drill holes right through the beams and place them on top of the rods.
After bolting the beams to the base, the rods were cut to size again to create an even base on which the first layer of the garden shed could be placed.

After the first layer was placed correctly over the beams (this actually took quite a lot of time) it was fixed with angle irons and the remaining layers could be placed on top. Once the first layer was in place, building continued at a steady pace.

At the end of the first day, the shed was built together until the roof level.
The following day the modification of the roof could start as planned.

Modification to roll-off roof

In order to get from a standard pre-fab garden shed to a fully functional astronomical roll-off roof observatory a “few” modifications need to be put in place.
The most important modification is ofcourse separating the roof from the rest of the construction.
The problem however is that these pre-fab sheds get their stability from the roof being put on top of it.

Separating the roof from the rest of the shed, needs to be accompanied by quite a few modifcations to the base construction in order to regain the stability previously provided by a fixed roof.

We started off by sawing the top layer of the shed exactly in half (see image to the left). The top part of this layer was going to be attached to a large beam which was part of the roll-off frame.

Next a set of beams was prepared, one beam with the wheels attached to it and another with the aluminium rail in which the roof could be rolled off. (see image to the right).

The second image to the left shows the upper beam with the half of the top layer (not visible), the wheels attached and spacing applied on top of one of the walls.
The exact height of the inner frame was calculated from this test setup.

The inner frame was first put in place to get a stable setup on which to place the modified roof construction.
As shown in the image to the right, the beams which were used to fix the shed to the concrete base were also used to create an internal framework to carry the weight of the roof and increase the stability of the pre-fab shed.
Besides these large beams also smaller ones were placed vertically to further increase the stability of the construction.

With the inner frame complete and in place, the next step was to create a rectangular frame which forms the basis of the roof construction.

As soon as this frame is done we should have a sufficiently stable inner frame as well as a basic roof frame, so the roof can be put in place.

Besides this rectangular frame, I decided to not place any other additional beams in the roof as the stability would come from the standard beams delivered with the shed and from the roof boarding
which was screwed onto each beam (3 beams on each half of the roof).

This would also keep the weight of the roof within reasonable limits. (I can lift the roof out of the rails on one side)
The beams used inside the observatory were again also used outside to construct the outward roof travel. Just a matter of extending the beams and aluminium rails outside.

A vertically placed beam inside a concrete base (the same hollow concrete reactangle filled with concrete) used for the observatory base was also used to support the outside beams.

Just remember to do some test runs of the roof to check if the aluminium rail is placed exactly right and the roof is rolling smoothly through the rail.

Details

With the inner framework, outer extension and roof in place, all that remains is putting in a floor and about 100 small other things….

Looking at the image above and right, you can clearly see that there is enough space available to put the floorbeams onto the first beam with which the shed is attached to the concrete base.

The most important rule to follow when putting in the floor is that neither the beams not the floor itself should make any contact with the pier on which the mount will be placed. This to prevent any vibration when walking on the floor to be transferred to the pier.

Any vibrations transferred from the floor to the pier (and therefore also the mount) will effectively ruin any image taken at that moment.

Also make sure to leave enough room around the pier for the floor to expand and contract.

When constructing the floor, we also attached several standard PVC tubes under the floor beams for putting in cables which run from the pier/mount to the (planned) wall sockets and laptop(s). I used 2 tubes side by side to separate data and electricity cables. There is a detailed image available from the list of images at the right showing the pvc tubes under the floor.

A small galvanized fence was placed between the bottom beam and the ground to prevent any creatures from crawling under the observatory.

Other things which were done was insulating the roof, mostly to prevent any resin from the wooden boarding dripping onto the equipment on a hot summer day. The thin foam was simply stapled to the roof boarding.

Wall sockets were installed based on a new power cable from my garage to the observatory.
Light was also installed including a dim red light in order to maintain night vision when reading a sky atlas.

Finalisation

This section just deals with any left over small details which were put in place to actually complete the observatory.
Again, most of the images can be found in the image bar to the right.

Some custom made furniture was placed in one corner on which one or two laptops could be placed along with some of the smaller instruments and some small pieces of equipment.

The large PVC tube which was used for the pier was painted black and a large steel plate (also painted black) was put on top of the rods, ready for the mount to be attached.

Locks were attached to the roof so it can be secured when closed.

Safety stops were attached to the outward beams to stop the roof at maximum outward travel.

An additional power socket was placed on the outside of the observatory to have an additional power source for garden equipment.

Regrets

A short overview of things I would do differently if I had to build an other observatory.

Additional beams were put in place between the final roof beam and the beam containing the rolling mechanism as the outward expansion of the roof caused the beam to be forced inwards also pressing the wheels into the back of the aluminium rails. (see “Roof stability increase” image in the right image bar).

The aluminium rail was replaced with a wider one and instead of using a “U” shape rail, an “L” shape rail was used. This allows a greater amount of expansion and contraction of the roof without the wheels getting stuck inside the rails.

The outward roof travel was extended (by extending the outside beams) in order to see Polaris through the polar scope. The offset of the pier was not sufficiently compensated by allowing the roof to be rolled off further.

Links to other observatories

Nineplanets.org – very extensive amateur observatory list !
A wealth of information on observatories can be found at the Cloudy Nights observatory forum.
Another observatory list, this list is however incl. link verification.
Roll-off roof design observatory.
Almira Observatory UK
Roll-off roof observatory planning and construction (German site)

Framing the garden shed

Determining pier height

Pouring concrete

Plywood & rods

Pouring pier finished

Concrete blocks

Concrete block w. beam attached

End of day 1

Height inner frame

Preparing the roof

End of day 2

Keeping out (small) visitors

End of day 3

Floorbeams in place

Pvc tubes

Floor finished

Finished pier

Finished observatory (1)

Finished observatory (2)

Custom made furniture

Locks

Roof insulation

Safety stop

Roof stability increase

Replacement aluminium rail

Finished observatory interior

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