Amateur Astronomy and Imaging.

Projects > Observatory


The chosen area for the observatory before carrying out any work.

When my interest in astronomy was predominantly based around visual observations things were very much simpler than they are today. I was able to set up my 6" Maksutov Cassegrain on my Synta EQ5 mount in about 15 minutes. Admittedly it usually took an hour or two before it had cooled sufficiently to allow high resolution imaging, but the point I'm trying to make is that setup times were short and were never a reason to prevent me from setting up. About 5 years ago I decided to attempt some fairly basic planetary imaging using a modified webcam. I was pleased with the results I achieved and soon turned my attention to deep sky astrophotography. Initially this included only the brightest objects, such as the Orion Nebula, Hercules Globular Cluster and the Andromeda Galaxy. From the start it was clear that I was going to have to make a few changes to get even mediocre results. The first change I made was to replace the Synta EQ5 with something more stable. It was frustrating to use, extremely poor quality and I wasn't able to achieve exposures longer than 30s before the utterly useless clutches would slip. I replaced the EQ5 with a Losmandy GM8 and haven't looked back since. It's a fantastic piece of kit, though it is quite a bit heavier.

I was much happier with the GM8, but soon realised that to get the results I desired I would need to start autoguiding. It was at this point that my setup times dramatically increased. Dragging the kit from the house to the garden was only the start of the process. It was also necessary to polar align the mount, balance the scope and autoguider, connect all the cables to a laptop and carry out an alignment using several stars. Once all this had been achieved it still remained to focus both the imaging scope and the guider, to select and frame the imaging target of the evening and finally to calibrate the guiding software. Assuming everything went well and was carried out in the correct order I could usually start imaging within about 2 hours. On many occasions clouds would roll in mid way through set-up and I had no option other than to start putting everything away again. Even the tear down process would take an hour. As you can imagine, I would only set up if I was quite certain the skies would remain clear and to make it worthwhile I would only do this if I could spend most of the night imaging without worrying about going to work the next day. The end result was that on average I only did this once a month or less.

After clearing the chosen area for the observatory of bushes and weeds and trying to determine the best size. Observatory plan. Observatory plan I sent to Alexanders Observatories.

The obvious solution to this problem was to change to a permanent setup. So, after several years I started the lengthy process of planning and building an observatory. While a dome may have certain advantages, I wasn't keen to put one in my garden simply because they don't look particularly attractive and are a good way of advertising the fact that you may have equipment inside (which in my case wouldn't be true anyway since I didn't plan to leave anything expensive in the observatory). After carrying out a little online research I finally decided upon a roll-off roof observatory as it would blend in better with the surroundings. I came across the Alexanders Observatories website and liked the style and design of the observatories. At this stage I had no idea of the size I would need or even where I would put it!

I don't have a particularly large garden but since my intention from the start was to remotely operate the equipment from the house I wouldn't need anything particularly large. The best views of the sky are undoubtedly found in the very centre of my garden, but I was fairly sure my wife wouldn't be happy with that idea! My house obstructs much of the sky to the North West and a line of trees at the bottom of the garden blocks much of the view to the South East. I finally settled upon a location at the side of my garden simply because it was the most convenient and had a reasonable amount of sky coverage. This particular area was also overgrown with thorny bushes, wild grass and a rockery neither me or my wife particularly cared for.

The first step took place in November 2010 and involved removing the bushes and wild grass. Once this area was cleared I was able to start determining the maximum size for the observatory. One of the drawbacks to a roll-off roof observatory is that you need to allocate an area the same size as the shed to allow for the roof to roll off. I realised that the most practical size would be an 8ft by 6ft design with the roof rolling towards the house in the North West direction. I could maximise my horizons by opting for a rolling side panel on the North East side and a fold down flap on the South West side. My horizons would be restricted, but I had to make the most of what was available.

My wife and I decided that we should make a number of other changes to the garden as part of this work which did incur much additional delay. The fence panels down the side of the garden where I planned to place the observatory were in severe need of replacement. It made more sense to do this before the observatory was installed. We also decided to remove the rockery, and rebuild the garden steps. We agreed that we'd remove the rockery and build a sandstone retaining wall, in the process levelling the area between the observatory location and the wall.

After replacing the fence and garden steps.  Rockery removed and retaining sandstone wall constructed.

With winter approaching not much else happened in 2010. I covered the area with plastic sheets to prevent weeds from growing and set about arranging the replacement of the fence. In February 2011 work finally began with the replacement of the fence panels. At the same time the garden steps were replaced and significantly widened for safety reasons. The rockery was removed and the sandstone retaining wall constructed. Even at this stage the garden was starting to look significantly better than it had previously.

The next stage was to prepare the hole for the pier. After much deliberation I decided I would bolt my pier to the concrete base after the concrete had dried. I know some people choose to bury a bolt cage in the concrete while it's still wet for extra strength. I preferred not to do this because I didn't want to use a pier with levelling bolts at the top (more on this later). I planned to use a pier that would need to be installed in polar alignment. I couldn't think of an easy way to do this with the concrete still wet so I decided to worry about installing the pier later. I dug a hole approximately one cubic metre in size. I live in an area with a significant amount of clay and this made for a hard time digging! It took me a good day to reach the required depth. After I finished digging I built framework out of wood that I would use to provide a square and level surface to the pier base once filled with concrete. For additional strength I placed a number of steel reinforcement rods inside the hole, though it's debatable that any additional strength would be needed for such a large mass of concrete. I also decided to fit an earthing rod, since I thought it might be beneficial to provide a local earth connection in the observatory and it was a simple task to achieve before I filled the hole with concrete.

I had naively assumed that if I placed an order for concrete that a large lorry would turn up and pump the concrete to wherever I needed it. I phone call to my dad who is more experienced in these matters soon put me right! He informed me that although pumping is an option, it would be very expensive and that realistically my options were either to mix the concrete by hand or to use wheelbarrows to run the concrete from the lorry to the hole. Access to the garden is by means of the garage and up an incline. The closest the lorry could get would be about 30m from the hole so it wasn't going to be easy. It still sounded like the preferred option, so I placed an order with Easymix (as they mix on site in the lorry meaning that you won't come up short or have concrete left over). I ordered one cubic metre for a cost of about 130. Realising that each wheelbarrow full would weigh nearly 100Kg it wasn't going to be easy to pour this in the hole without disturbing the frame which needed to remain level. I decided to fit a block of wood securely held in the ground by steel rods about 10cm from the frame itself. This was used as a bumper to prevent the wheelbarrows from disturbing the frame.

After digging the pier hole and adding steel re-inforcement rods and Earth rod. Shown on the right is a wooden block fitted temporarily to prevent wheelbarrows from knocking framework off level while pouring the concrete. Filling the pier hole with concrete.

I placed scaffold planks up the garden steps to make it possible to run the wheelbarrows to the pier hole. I was told by Easymix that we had about 20 minutes before the lorry driver would need to leave site. It didn't seem like long to me but my dad assured me it would be enough. He had offered to help me run the concrete into the hole and by the time the lorry arrived we were both ready and waiting. I lost count of the number of wheelbarrow runs we made between us, but I'm sure we had the concrete in the hole within about half an hour. It was hard work, but I'm happy to say that the wooden bumper worked admirably despite ending up about 1cm from the frame. The frame remained level throughout and after tamping down the concrete and levelling it with wooden boards across the surface we covered it by resting it with planks rested against the fence. This helped prevent the rain from affecting the surface. What I hadn't accounted for was a neighbouring cat that felt obliged to walk across the surface before it had set! Luckily I spotted the paw prints in the concrete before it had set and managed to smooth them out, though in doing so I affected the final finish. I decided to wait several weeks before any further work took place.

The next step took place in March 2011 and involved digging a trench about 18" deep and 6" wide across the garden. My plan from the start was to control the equipment from the house and in order to do this I would need to provide mains power and data connectivity to the observatory. I decided to run 2.5mm SWA cable from the house, across the garden to the observatory. The cable was rated at 36A which is much higher than I need, but I decided it was better to overspec than underspec. For data connectivity I used two CAT5e cables which I ran through corrugated conduit. I hadn't realised how difficult it would be to get 25m of CAT5 cable to emerge out the other end of the corrugated 25mm conduit. It took an hour or so but finally I managed with the help of talcum powder. With the SWA and conduit in the cable trench I proceeded to fill the trench back in. I laid the cables 24" deep where I crossed the flower bed and next to the observatory and covered the cables with bricks to prevent garden instruments from damaging the cables in the future. Since I plan to control the observatory from the conservatory it was here that I installed the network ports. After two days of digging and cabling this stage of the project was complete. The cables at the observatory end were placed in a bag and covered to prevent damage from moisture.

Concrete pier base after concrete had set and framework removed. Laying mains cable and CAT5 cable conduit in trench. After refilling the cable trench.

It was at this stage that I placed the order for an 8ft by 6ft observatory. As I now had all the information I needed and I knew I would need to wait about 3 months before the installation would take place I went ahead and paid the deposit to Alexanders Observatories. What I haven't yet mentioned is the debacle concerning the pier! Before the end of 2010 I had carried out extensive research into the available pier offerings. I decided I didn't want one of the piers available with the levelling bolts at the top simply because the stability of the pier is reduced to the bolts themselves, of which there may only be four. Granted, it does make for easy installation but once I learnt that the pier itself doesn't need to be precisely level I realised this didn't matter. Most mounts can be adjusted to account for a pier that is not level so as long as I installed the pier ensuring it was close enough to polar alignment I should be able to do the final adjustment on the mount itself. The research I carried out suggested that the diameter of the pier was the factor that provided the most stability. Thicker walls on the pier material help too, but not nearly so much as additional diameter. I eventually chose an AC421 pro pier from Astro Engineering. I ordered one with the Losmandy marry plate just before the end of 2010 before the tax rate increased in the new year.

I visited the store to place the order, and discovered that three separate companies are based under the same roof. Scope n' skies and Pulsar Optical seem to be the customer facing parts, while Astro Engineering make many of the products and don't deal directly with the public. I was treated well in the store and when I placed the order I asked if the pier could be customised to include two holes which I would use to fix the brackets for my Gemini system. To help them carry out the customisation I left them my Losmandy extension tube with the Gemini brackets attached.

After several weeks when the Christmas period had passed I received a call from Robert Dalby asking me to confirm my requirements as he was about to start work on the modification to the pier. When I explained to him what I wanted he suggested that it may be better if the brackets were fitted to the marry plate instead of the pier. I wasn't sure if there would be sufficient clearance by the mount if the Gemini was attached to the marry plate so I wasn't able to confirm if that would be acceptable over the phone since I was at work at the time. It did mean this would delay the modification until the following week, but that wasn't a problem for me. The following week I confirmed that having the brackets on the marry plate would be fine and was told that work would start on the modification over the next week. It was late February before the pier finally arrived! Not really a problem since I was in no rush.

Network port and conduit work in the conservatory. Astro Engineering AC421 Pro Pier.

However, there were two problems. Firstly, they had forgotten to supply bolts for fitting the marry plate to the pier. Secondly, and more importantly, the holes they had drilled into the marry plate provided the wrong separation between the brackets as they were too close together to fit the Gemini unit. How could this mistake have happened if I left them my Losmandy extension tube with brackets? What happened is that they measured the distance between the holes on the extension tube and drilled the holes on the marry plate the same distance apart. What they had neglected to take into account was the fact that the marry plate was a larger diameter than the extension tube! A simple engineering issue which ironically I had considered mentioning when I asked for the customisation. I chose not to simply because I expected that experienced engineers would know far more about these things than I do! I wasn't best pleased with either of these problems, but in fairness they did ship me the bolts quickly and also gave me one of their own Gemini brackets free of charge as a temporary solution.

Even at this stage I wouldn't have minded too much if a prompt resolution was forthcoming. However, what followed was two months of regular phone calls before a solution was reached. Earlier in the year I would have to phone 20 times or more before the phone was answered. I was told this was due to increased demand on the shop floor following the Stargazing Live event on the BBC. I believe this to be true as in the weeks that followed the phone was answered more promptly. However, I lost count of the number of times that I was told the person I needed to speak to was with a customer and would return my phone call. Yes, you guessed it, my call was very rarely returned! By April I reached the point where I was happy to return the pier if a resolution could not be reached (after all, I wasn't asking for a major customisation here!). One of their staff who would usually answer the phone, a young sounding lady, always came across as not wanting to be there and I always wondered whether she actually passed my messages on. I always got the impression that it was a major inconvenience for her to take my phone call. So, by mid April I finally decided that the best way to reach a resolution was for me to arrange a time to visit the store and to collect the marry plate. Robert wasn't keen for me to arrange a time until he had a guarantee from Astro Engineering that the work would be completed in time. Finally he agreed for a meeting on a Friday morning with the expectation that the work would be completed several days beforehand. It came as no surprise to me that on Friday morning the aluminium blocks were still on the workshop floor waiting to be machined (let alone customised). When I arrived at lunch time they had constructed the marry plate and were about to start the customisation. Robert suggested I went to the town of nearby Ely and returned later. This seemed like a good idea to me. 2 hours later they still hadn't started, but by this time I was back in the shop and Robert suggested a visit to the machine shop was in order. He gave me a guided tour as they completed the work in front of me. Finally, on 15th April the saga was over. I can honestly say that I'm happy to put all that behind me. Robert did offer me a free book from their collection but I declined the offer. I feel that I was a victim of ineptness from Astro Engineering and very poor customer service from Scope n' Skies. Would I buy from them again? Perhaps, but only if it was something off the shelf.

Paving laid in preparation for observatory. Paving laid in preparation for observatory.

The next stage was the installation of the paved base for the observatory. This took place late in April and included the installation of a new garden path from the steps replaced earlier in the year. The area next to the observatory, which was previously the rockery, was also levelled and grassed. I left a 2cm gap between the paving and the concrete base which I filled with builders sand. Hopefully this should help reduce vibration transfer to the pier, although I don't plan to control the observatory from inside it.

It was sometime before there was any further work on the observatory project. In May 2011 I decided to mark the location of the holes for the pier on the pier base. As the mount bolts to holes in the marry plate, I needed to make sure that I polar aligned the mount on top of the pier to determine where the holes would need to be for the correct pier placement. Obviously I had to do this at night using the polarscope on the mount. What made the process more difficult was that the pier is designed with a slightly curved base (the base is convex). The reason for this is that when it is bolted down the curvature is removed and the pier is under stress which helps dampen vibrations. What I hadn't realised is that in the very centre of my pier base there was an area nearly the size of the pier base that was slightly recessed. I created this when I removed the paw prints! My solution to this problem was to move the pier slightly off center.

I marked the location of the pier holes and one weekend in May I set about drilling the pier holes. I borrowed my dad's SDS drill as my own drill would barely scratch the surface of the concrete. I was quite concerned that if I didn't drill the holes accurately I wouldn't be able to fit the bolts through the holes in the pier. For this reason I took my time and worked my way up from smaller drill bits all the way through to the final 18mm drill bit. I spent about 4 hours drilling the holes before finishing. I was very happy to discover that I had drilled the holes perfectly in alignment with the holes on the pier. The following day I cleaned the holes using a vacuum cleaner with a piece of garden hose the exact same diameter as the holes. It was a perfect way to remove all the dust from the holes before I used the resin compound to fit the stud bolts in the holes. The resin compound is workable for about 5 minutes and I was concerned, after reading articles posted by others, that if the two chemicals don't mix correctly on application that the resin doesn't harden. I chose to discard the first 15cm or so of resin, and only started filling the holes after I was sure the chemicals had thoroughly mixed in the nozzle.

Drilling the bolt holes in the pier base. All of the bolt holes drilled.
Stud bolts fitted to pier base and tested for size with pier. Pier fitted and awaiting the arrival of the observatory.

After the resin had hardened I removed a little that had found its way onto one of the bolts. It dries very hard so it was necessary to file it off. I tested the bolt placement once again by gently placing the pier on top. I was happy to discover that the pier fitted precisely. I was careful not to let the weight of the pier strip the threads of the bolts as I tested it for size. I removed the pier from the bolts and returned it to the house because I knew it would be several months before the observatory arrived.

After several months of waiting I finally received a text message from Nick Evans informing me that my observatory was ready for installation. We agreed a date for installation, and several days before he arrived I fitted my pier to the base. According to the instructions on the resin tube, I should apply 50Nm of tightening force. I wasn't sure how much this was and was a bit concerned I might over tighten them. In the end I got the bolts as tight as I could by hand with a spanner about 25cm in length. I noticed that after I finished tightening the bolts the pier made a higher pitched sound when I tapped it and the sound died out much more quickly than before tightening. I covered the bolts in grease to prevent them rusting and waited for the observatory installation.

Nick arrived exactly at 8am as he said he would. I gave him a hand carrying all the parts through to the garden and he set about installing the base. Much of the observatory he had pre-fabricated and the on-site work involved fitting each of the components together. Once the base had been laid the side panels were fitted. The panels have a plastic layer inside them to help prevent moisture leaking inside. The panels are then covered with plywood which forms the inside wall. After each of the walls is fitted the wooden beams that take the weight of the roof are installed. As my garden is not level the beams needed to be slightly longer than Nick had planned. So, while Nick carried on with the installation I went down to my local builder's merchant to buy a longer post. Nick cut the new post to size upon my return and shortly afterwards he started working on the roof. There's a huge amount of work that goes into the roof and it's fair to say that Nick's observatories are more "log cabin" than "shed". He takes a lot of pride in his work, that's quite clear from the end result and the way he works. I was very happy with the finished product and ready for the next stage of the project; installing the cabling.

Over the next few days I started the process of installing the electrics and the CAT5 socket. I fitted an IP65 rated consumer unit within the observatory with two separate MCBs. One rated at 32A used for the mains sockets and the other at 16A for the light. The light, switch and mains sockets are all IP65 rated. I chose to use blue arctic cable (1.5mm for the lighting circuit and 2.5mm for the sockets) and ran this inside the observatory walls (another benefit of a wooden roll-off roof design over a fibre glass dome). When I first tested the light I was a little surprised at how dim it was, but I'm happy to report that it's certainly bright enough when used in the dark. I fitted the CAT5 data ports, making sure I installed them so port 1 in the observatory is port 1 in the conservatory. I wired these as straight through connections so I can use standard patch cables at either end. A month or so later I painted the walls, floor and cupboard inside the observatory black. While it may not look so good, it does significantly reduce reflected light levels inside the observatory.

Observatory base fitted. Observatory walls fitted. Runner for roll off roof.
Cabling inside observatory walls. Front view of observatory. Side view of observatory.
Inside observatory. Inside observatory after painting interior black.

My intention is to sit with my laptop in the conservatory and use a small form factor PC in the observatory, which I will control over RDP (as it's running Windows). All of the software will be on the PC in the observatory and the laptop will be used to provide the remote connectivity only. The observatory PC will run the Gemini Control Center software to connect to the mount and cameras etc. via my Astrohub (this can also be found in the projects area of my website).

Although I don't plan to sit inside the observatory all that often I have fitted a small cupboard, a desk and a chair in case I change my mind at some point. I've also added a digital thermometer/hygrometer which should make writing my imaging reports more accurate. Finally, to finish the observatory I installed additional security within the observatory and connected this to the home security system. Although I don't plan to leave telescopes or computers in the observatory, I feel it gives me peace of mind.

Paper azimuth and altitude scales used to determine horizons. Cartes du ciel representation of skies using horizon information.

Before starting to use the observatory I decided to determine my lowest visible horizons. To do this I created a circle which I marked in 20 degree increments of azimuth. I placed this circle on top of my pier. I then placed a semicircle marked at 10 degree increments of elevation at right angles to the top of the pier. For each 20 degree increment on the azimuth circle I recorded my lowest visible elevation above the horizon by sighting with a ruler against the elevation semi circle. I took readings at every 20 degree increment from 0 degrees (North). I then fed this information into Cartes Du Ciel which can then determine the sky visible using this horizon information at any date and time of the year. My North West horizon is obstructed by the observatory roof, something I may be able to adjust in the future if I configure the roof to roll off slightly further. My South West horizon is obstructed more than I would like by one of my trees. This may need a bit of a trim in the not too distant future!

As I've only just completed the project I haven't yet had a chance to start using it. No doubt there will be a few teething problems, but that's half the fun of amateur astronomy! Hopefully my imaging results in the future will improve, and if not at least I should get more regular practice.