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Considerations About Building an Observatory

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Building a Personal Observatory Part One

It was suggested that I write down some of the things that I learned in the process of building my own home observatory. I agreed to do this because I find that you often crystallize your thoughts when you stop to write them down. The first thing that I would like to make clear is that these are only one person’s ideas and should be weighed against the input from other sources. This first installment may appear to not progress very far, but I believe that these first steps are the foundation for a successful observatory process that will provide use for years to come. They are also, in my experience, some of the hardest steps and can take months of thought, investigation, and discussion.

Before I start with my thoughts on this project I would like to mention that there are several books out on the subject, including: Building and using an astronomical observatory by Paul Doherty, distributed by Sterling Pub Co. © 1986 and both Small Astronomical Observatories: Amateur and Professional Designs and Construction © 1996 and More Small Astronomical Observatories © 2002 both by Patrick Moore, and published by Springer. Some information is also contained in StarWare by Philip Harrington, published by John Wiley and Sons, Inc. © 2002. There are also discussion groups which are an excellent source of first hand information. Here again, you need to be cautious regarding which opinions you accept. People are seldom willing to admit that they made a mistake and will strongly support whatever they have done. Some of these discussion groups include: Yahoo groups – (Observatories, Roll_Off Roof, skyshed, siriusobservatories_users, Homebrew_Telescopic_Piers, GeodesicObservatories, Observatory_RoofandDome_Automation, and Astronomical_Observatories). There is also a site that lists many small amateur observatory sites, ( One web site that I found that offers an inexpensive method of adapting a plastic shed can be found at ( Finally the manufacturers/installers of home observatories offer information that can assist in this process. The theme here is talk to as many people as you can and read as much as your have time and interest permit. That said, let me offer some of my thoughts on the process.

I believe that the first step is the most crucial one in this process as it is with most projects. For me the first step was finding the answer to the question, “Why do I want a personal observatory?” While this may seem to be straightforward, I strongly recommend that you spend some time investigating and clarifying the answer to this question. There can be many reasons to want a personal observatory, but the ones that are most important ones to you will greatly influence the subsequent choices that you will make.

The most important question is whether you are primarily interested in visual astronomy or astrophotography. If it is visual, then you will want a site with good horizons and with dark skies. This may force you out of your backyard if your home is in a typical suburban neighborhood. If your interests tend toward astrophotography, dark skies are less critical. Although dark skies make imaging and image processing substantially easier, so I wouldn’t discard the idea of looking for a remote location yet. Is weather a strong impediment? Do winter winds and temperature often keep you inside? The shelter afforded by an observatory may make more days of observing possible for you.

The next question centers on your emotional reaction to your past and future observing outings. Are you fired up and anxious to get going? I would wonder if you want to spend monetary resources and energy on a personal observatory. Is some degree of inertia beginning to intrude on your enthusiasm? If this is the case, then I would ask your self why? Is the problem one of the inconvenience of packing up, setting up, breaking down, and unloading? Is the problem that you are having difficulties handling the set up and break down of your equipment due to physical considerations? Is there a factor based upon the limited time you have available to go observing? For example, I was finding that by the time I set up in my driveway and aligned my telescope, somewhere from 30 minutes to an hour depending upon which telescope and which mount I used, often the skies had become substantially cloudier, and my brief window of time to observe was gone. This didn’t have to happen too many times before I knew that I needed another way. Are you limited in your ability to observe during the week because of job considerations and not other commitments? Then travel may not be an option except on the weekends. The need to get to bed at a reasonable hour will curtail your observing time and make set up and break down a more significant portion of your evening. If these problems can be eliminated, then it may still be possible to do some observing during the week.

It should be evident to most readers that the answers to these questions will help you decide whether you want to build on your own property or whether you want to look for a darker remote site. For example, if personal obligations make it impossible for you to observe during the week, and vacations and weekends are your only opportunity to observe, then travel is not a major impediment and perhaps you would be best served by looking for darker skies. However, you need more than a simple answer to each of these questions. You need to determine the hierarchy of your answers to these questions. If convenience is the most important factor then your may not want to observe far from home. If set up convenience is paramount to you, but not travel, then a more remote, but darker site may still work. If you are totally committed to visual deep sky observing then you need to go to a dark site regardless of convenience. When you have your own personal hierarchy you should be able to decide where you want to construct it.

In my particular case, I noticed that the weather was frequently uncertain and I needed to turn in on week nights early enough to get a full night of sleep. Since I also am most excited about astrophotography, there was additional setup “overhead” involved that had to be done each and every night of imaging. Added to this was the fact that my physical conditioning does not make it easy for me to move and to set up many larger imaging telescopes and mounts. I also became aware that my recurring problem of kidney stones, which are unpredictable, sudden in onset, and prevent me from driving once they start,

made a remote location a bad choice for me unless I always had someone with me. Even then, a long ride home would be intolerable. For me, this last factor became the primary one in the decision to build in my backyard. The skies are sufficiently dark to allow imaging and having everything set up and ready to image only a few feet from my back door would increase the amount of time available for imaging even when the clear skies fell on a week night.

Once you know where to build, the next obvious question is what to build. This question also seems simple, but for me it required a lot of research. The type of structure came first, dome or roll-off. The dome has the advantage of better protection against the elements and better protection against ambient light. The latter fact is helpful in preserving night vision. This would be a greater factor for visual astronomy

in suburban sites. Since I was not concerned with visual it was less of an advantage for my interests. For others, it would be more important. There are several drawbacks to domes that I am aware of. According to some sources, there is some indication that the dome design is more aerodynamic, making it is more resistant to winds. The very same factors that protect you from the elements, namely the small exposed area, make the temperature equilibration slower with a dome. Additionally, this small opening creates a greater tendency for convection currents while there is a temperature difference. Those currents also happen to be in the path of your optical tube which can be a problem for both visual and imaging work. This is clearly not an insurmountable problem given the fact that most professional observatories are domes. You must plan ahead and open the dome to allow for temperature equilibration before observing. Another drawback of the dome design is the fact that in any given orientation there is only a small portion of the sky visible. This means several things. You may not be aware of bad weather approaching from a blind spot. You won’t be able to see a lot of the sky at any one time to assist in visual orientation. There is also a lost aesthetic quality to only seeing a slit of night sky as opposed to being under a canopy of diamond covered velvet. Probably the most significant issue is that the dome needs to be moved in concert with the optical tube assembly (OTA) in order to move to different objects or to track an object while observing or imaging. This means that you need to keep moving it either manually or by some type of motorized mechanism. While imaging you may need to provide some means of automation to synchronize the movement of the dome to the movement of the sky while imaging. Such automation systems are available, but they will require computer control and a reliable source of electrical power, neither of which comes cheaply. Power may also be a significant problem in remote locations.

Recently, portable domes that can be erected or broken down in a couple of hours were developed. This makes it possible to bring your observatory up to a summer cabin and then bring it home after your vacation. It also makes it easier to take your observatory with you if you ever move. This may be relevant if you are uncertain as how long you will reside at your current residence or if you regularly vacation where there is good observing. Finally, but not insignificantly, the appearance of a dome must be considered. This may be a “show-stopper” for your spouse. It may also be a problem for your neighbors which can then become your problem if you live in a neighborhood with a home owners’ association. If you are planning on building on your primary residence property, a dome may have a negative impact on your property’s value at the time of resale, unless you find your home buyer on AstroMart, in which case it may actually add to your home’s value! Another consideration about the appearance of a dome, whether you build in you back yard or on a remote site, is its unique appearance is an unmistakable advertisement as to its content. If you have any concern with vandalism, you are not going to be able to disguise your observatory if you select a dome style of construction.

The advantages of a roll-off observatory design include a more rapid temperature equilibration. There is greater sky exposure so you are less likely to be blind-sided by bad weather. It is easier to orient yourself in the sky when trying to locate an object. There is also something to be said for being out under the stars and a roll-off design definitely provides this. Rolling off the roof can be done manually in many designs which can help to reduce construction cost. Even if you elect to motorize the roof, there are several designs which are relatively simple and inexpensive. Once the roof is off, it provides obstruction only in the direction where it rests in the open position. For this reason, you should plan to have your roof roll off in the direction you are least likely to observe. This could be the direction of another immovable obstruction such as your house, or it could be the direction of the sky you feel least likely to wish to observe in perhaps due to a light dome. If the size of the observatory and the height and position of your pier are selected carefully the roof is a relatively minor obstruction. All that being said, once the roof is off, you don’t have to move it again until you are ready to close it. This makes for unobstructed tracking without the need to have the roof follow the OTA as was the case with a dome. If you elect to automate remote roof opening and closing, much less complicated software is involved. If this is to be automated remotely, you may need to provide some detection for obstructions to prevent the roof closing into your mount or OTA. This is only a problem for the most advanced designs when imaging is the object of the observatory.

The roll-off design more closely resembles normal building or shed construction. Therefore, it is more easily constructed by the average do-it-yourselfer or average contractor with a little guidance. Additionally, the roll-off design has, from a home owner’s perspective an advantage since it can be made to fit in with the neighborhood more easily. In my case, adding shutters and planter boxes made my observatory acceptable to my spouse and, apparently, to my neighbors. The building resembles a play house for children or possibly a potting shed. Neither of these seems to be a high priority target for vandals. This is a quality that I find highly attractive. Similarly, if this were a remote site, the roll-off could be made to look like a small camping shed that would likely be passed over by people passing by. A dome, on the other hand, practically cries out to be investigated. If I were to leave the building, then the next buyer could likely find several uses for it even if they never owned a telescope. As my installer’s wife suggested, if you get tired of astronomy, a roll-off observatory makes a great place for nude sunbathing.

Just as with the dome, many of the advantages of the roll-off design are also responsible for its drawbacks. Since the roof opens to the sky, the observer is exposed to the sky. During times of severe cold, this can make observing less comfortable. The walls will still provide significant shelter from wind and wind chill effect so it will be better than an open field. Similarly, if there is significant ambient light from automobile headlights of unenlightened neighbors, a roll-off design will expose you to more of this. This could be a consideration if you are doing visual work and need to maintain dark adaptation. It is less of a drawback for imaging.

The construction of a roll-off observatory is likely to be much heavier than most of the personal dome observatories due to the materials involved. Consequently it is unlikely that it will be movable if you ever move. The SkyShed design reportedly can be constructed in sections (subject to certain size limitations) that can be disassembled and transported to a new location. I have no experience or first hand knowledge of this feature, but I am concerned that the structure could be damaged during disassembly or transport. This should be explored fully by anyone who intends to make use of this feature. The roll-off design also presents greater challenges during storms. Since the roof rests on rollers it may be prone to being blown off by strong winds so some measures must be taken to prevent this. If it is heavy enough it may provide some defense simply by virtue of its weight. Alternatively, a system to latch the roof to the walls should be included. One designer is looking into a system where the rails wrap up over the wheels thereby making it hard for the roof to lift out of its tracks. In my observatory there are 3 turnbuckles that were installed to secure the roof to the walls.

Returning to the original point about knowing why you are building an observatory, if you only want a place to secure your setup equipment, then you might want to consider a different type of roll-off observatory where the building rolls off of the pier. While this provides no protection from the elements, once the building is off you have as much room around the pier as your property provides. Since you only need to build it large enough to house your telescope on its mount and pier, the size of the construction project can be substantially smaller and the cost is proportionally less. This may be a highly attractive consideration for some individuals. A couple of examples of this type of observatory can be found at these web sites: ( ( (

There are other varieties such as geodesic dome observatories which I won’t cover, but can be explored on the World Wide Web or at Yahoo discussion groups.

Next installment I will try to cover the deciding on the size of your observatory and the placement. I will also discuss the layout considerations and some considerations and steps that should be taken before you start. I will subsequently cover choosing a vendor, piers, and power.

Some Commercial Roll-Off Vendors

Backyard Observatories

Pier-Tech, Inc.


Some Commercial Dome Vendors

Clear Skys, Inc.

Sirius Observatories


Building a Personal Observatory Part Two

Well, after you have done your homework that I suggested in the first part of this series, you should know why, what, and where you want to build an observatory. I have no direct experience on locating another site for an observatory and I would defer to some of those members such as Frank C. and Gary W. to advise you on how to locate land that is good for a remote site. Please note that if astrophotography is your goal, don’t forget that you can purchase land for an observatory in places like New Mexico and run the observatory remotely. A number of current astro-photographers are doing just this. While the remainder of this series will assume that you are building on your own property, much of what follows is generally applicable to an observatory built anywhere.

If we assume that you are going to want to be in your observatory and that it is not simply a place to store your equipment in a fully set up position, then you are going to have to consider how big to make it. Clearly, zoning ordinances will come into play here as there may be restrictions on the maximum size of shed that is permitted. In some municipalities the size is calculated using the space occupied by the posts that support a roll-off roof. While this makes no sense at all, it effectively doubles the square footage of any roll-off observatory. You want to know this before the building inspector comes over and tells you it is too large and has to be torn down. Here also your local Home Owners Association may have restrictions regarding size and even style. An ounce of prevention is worth a pound of demolition so check this out right up front!

When I planned my observatory I thought that I would like to have room for someone to come over and image or observe with me. Even if I was alone I thought that while I was waiting for long imaging sequences to finish I could amuse myself with some visual work or possibly shoot widefield images with my TMB 105/650 while doing close-up images from the BRC-250 pier. All of these reasons made me feel that I would want to have room for 2 telescopes. But how much room would I need.

In East Pikeland Township where I am located, an outside structure up to 200 square feet requires a very simple and relatively inexpensive (around $140 including electrical inspection) permit and process. You build and they come and inspect. Above that size and the process required formal blueprints, certifications, and inspections, not to mention substantially more money. That settled the matter for me. I was going to keep it under 200 square feet. Fortunately, East Pikeland measures only the space within the building and not the space under the roof tracks.

The next question was whether this would be large enough for two telescopes. I drew and calculated and drew some more, but I was still uneasy. Then Gail suggested that I measure the dimensions out in our driveway and set up the equipment. It was simple and elegant. I got some electrical tape and a tape measure and marked off the dimensions. I then put up my telescopes where I thought that they would be best placed. After some walking around I decided that the scopes would be better placed to the front of the midline of the observatory. That way they had a slightly better angle for viewing over the retracted roof and there was more room toward the back to put in desks to hold charts and manuals and computers and all the stuff that seems to multiply out of control in this hobby. I could now see exactly how it felt to walk around the space. I decided upon 15 feet long to separate the telescope piers by 13 feet deep. This came to 195 square feet (less than the magic number) and gave me adequate space if not copious space.

The placement of the pier was my next concern. I wanted to make sure that my telescope would have the best horizons possible. If the pier were placed too close to a wall then I would need to raise the telescope above the wall to get any views near the horizon. This was possible, but it exposed the telescope to additional wind which might cause vibrations while imaging. Additionally, if the mount stuck up too high then there would be problems getting the roof to roll past it. There was the possibility of parking the telescope and mount in the horizontal position, but I felt that this made it less secure when closing or opening the roof. This would become an even greater concern once I started remote imaging. I would have to add additional measures to ensure that the telescope was clear of the roof. For that reason I elected to purchase a pier that could be raised and lowered and thus could be made to clear the roof when parked and still extend to a height that permitted adequate horizons. Once again, the best way of ensuring the horizons involved assembling the mount and scope on a table and getting accurate measurements of how high above the pier it would extend in various configurations. After that a little geometry allowed me to determine that if the concrete was flush with the floor, when I extended the pier I would have 20 degree horizons in all directions. This was more than I needed for astrophotography and more than I had with the back of my house and the neighbor’s houses situated the way that they were. If anyone wants to know how to calculate this, I think that I can retrieve the formulae and get you going, but lapsing into geometry may leave a lot of people bored.

The next issue that bothered me was where to put the observatory. I approached this in much the same way. I went out into the yard after dark and walked around while looking at the visibility. Again, for my decision I was measuring everything against astrophotography. While the least light polluted parts of the sky are the north and west areas, the east and south are attractive imaging regions. I can only see south from one back corner of my yard between houses. From everywhere else, my house blocks all but the highest portion in the southern direction. The rear corner with the southern exposure would have put the observatory right up against the forest behind my property. This would mean that I would have had no westward view past the meridian. This is not good for imaging when the light dome to the east won’t let you start imaging until the object it around 60 degrees above the eastern horizon. That leaves you only 30- 40 degrees of sky to use for imaging. This would translate into around 2 hours of imaging for any object rising in the east. This was not workable when modern exposures frequently use 2-8 hours of luminance time and equal or greater amounts of time for each of the red, green, and blue exposures. This doesn’t include if you want to add hydrogen alpha exposures to enhance the image. At the low end of 2 hours each, it would take me more than 4 to 5 nights to collect all the data for a single object. With the weather we have been having here in Pennsylvania that might turn into 4 to 5 months. Additionally, it would mean that I could only image an object of this path at a very particular time of the year when it rose into the 60 degree elevation in the east well after dark. If I waited too long to where it was overhead at dark, there would be virtually no time to image it from this point in the yard.

From the other side of my lot I was able to use the neighbor’s house to block the easterly light dome to about 45 degrees, but I could see to south east. This location also had a clear shot to the north and northwest, and there was a view to the west and southwest to about 50 degrees above the horizon where the tree tops of that forest reached. This meant that the circumpolar regions were virtually unobstructed to the east I could image from around 45 degrees to the meridian and then about 30 degrees beyond the meridian. This gave me, conservatively, 60 degrees of tracking for imaging which translated into 4 hours of imaging time. While still less than ideal it was about twice as long as at the other side of the lot. This was where I decided the best location would be, the north side of my property.

Another option for some people will be placing the observatory up on a deck. This has the advantages of elevating you away from ground effects and may position you above many of the obstructions that surround the observatory. This can translate into better horizons. It poses anther problem that must be addressed, how to make a solid pier. If the observatory is placed on a second story deck the concrete pier will have to extend from 36 to 48 inches below the surface of the earth up through the deck. The size of the pier for this expanse has to be enormous to eliminate vibration. Even 3 feet by 3 feet may not be adequate according to the calculations of some observatory engineers! This means an enormous amount of concrete must be poured and this may be more than a homeowner may be able to do without professional help. Still there are attractive features to being above the tree line and if possible it should be considered. or

At this point I knew how big the observatory should be and where it should go and where the piers would be inside of the observatory. From the location that I had chosen there was a slight grade of the lot from high on the northwest to low on the southeast as well as high in the north to low in the south. I knew that this grade would have to be addressed in the building. The observatory would be flush to the ground in the back but about a foot or two above ground level in the front. This would require a step in the front by the door. The next question was the choice of a vendor.

I did some serious soul searching asking whether I wanted to tackle this project myself or with the help of some friends. The SkyShed vendor sold plans and it looked like a possibility especially since they sold the parts largely precut and partially assembled. The Backyard observatory under inspection appeared, to me, to be more solidly built and the plans were for a more substantial building. That left me uncertain about my ability to construct such a heavy and large structure. Also the concrete work would require a lot of digging for the deck supports and for the two piers. Realistically I thought that this would take me most of the summer working on weekends and free evenings just to get the holes dug, and the supports secured in the concrete. Although it was more expensive, given the limits of my skill with construction and the limits of my time, I decided to arrange with Backyard Observatories to come and assemble the observatory on my site. This allowed for on the spot adjustments for unanticipated obstacles and ensured that the building would be done correctly. The details of the four days have previously been chronicled on the Chesmont web site along with photographs so I won’t repeat them, but I will say that I have never regretted this decision, even when writing the check!

Power is a concern for any observatory whether it is intended for visual use or for astrophotography. Initially, I had thought to use a battery farm with solar panels to recharge it. Later, I determined that the power consumption of all the devices I planned to use might well exceed what I could recharge in a given day using the available space on the shed roof for solar panels. That was when I decided to run a line from my house to the observatory. This is a possible place for cost reduction. If you are up to it, consider digging the trench before the electricians come to install the power conduit and lines. This can substantially reduce the cost of the job.

I put 2 separate trenches in order to separate my internet wire from the power lines. For the length of the internet run I had to use CAT6 cable in order to have adequate signal strength at the observatory. It was suggested to me, and I believe that it was a good idea, that you run at least two internet lines in case one becomes damaged. You can also run phone lines in this conduit as well. One last piece of insurance is to leave a draw string through the conduit so you can pull any other wire through at a later date should you need it. Because I thought that I might want to run air conditioning, dehumidifiers, or heaters out in the shed, I had the electricians take this into consideration when they installed power. They decided to install a subpanel box in the observatory that allowed me install surge protectors. They also installed a lightning arrestor at my request (This link will show what lightning is capable of doing to an observatory with a direct strike: ), but I have subsequently learned that this will not provide much protection in the event of a direct lightning strike. The only methods that will protect your equipment from this would cost more that twice what the entire observatory cost me. Get good insurance and pray regularly!

This is pretty much all of the advice that I can provide. If there are other areas that you would like to hear about, drop me a line and I will consider a follow-up to address them.

Chris Abissi

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