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Observatories: The Good, The Bad, & The Ugly:  Some Thoughts on Observatory Design and Construction

by Tim Hunter and James McGaha



Amateur astronomers dream of having their own observatory at a site with dark skies and good seeing. Observatories are wonderful and can provide endless hours of pleasure. Yet, they have to be designed and managed with care otherwise they can become expensive white elephants rarely used or enjoyed. In this essay we hope to alert you to some of the difficulties that arise in connection with an amateur observatory. Beware of common pitfalls and plan to avoid them (Table I). This is not to discourage you from building an observatory. Far from it. Observatories are marvelous. We only want to prevent your suffering some of traumas we have gone through with our observatory construction and operation.




1. Land costs: purchase costs; taxes; insurance; utility installation.

2. Hidden costs: fencing; grading, road improvements; building permits; well installation.

3. Costs for permanent observatory equipment (see below).


1. Roof too heavy and difficult to move.

2. Poor seeing conditions: use of improper building materials and poor observatory design.

3. Insufficient storage space; limited seating; no warming area

4. Horizon blockage by the roof or observatory walls.

5. Poor protection from the wind, rain, dust, and mud.

6. Thermal currents.


1. Theft and vandalism.

2. Light pollution.

3. Fire and lightening.

4. Generator breakdowns. No electric or phone service.

5. Insect and animal pests.

6. Ordinary wear and tear.



Most amateurs live in or near an urban environment and have to contend with light pollution and light trespass. Unless you can afford the luxury of having more than one observatory, one of your first choices is where to put it--in or out of town (see Astronomy November 1989, page 93). An in town location near your home has the advantage of ready availability usually at the sacrifice of dark sky conditions. Out of town has the advantage of a dark site at the sacrifice of convenience.

It is mandatory to select a site that has as good seeing as possible, because consistently poor seeing will severely detract from your viewing whether you are looking at the moon, planets, double stars, or deep sky objects. Seeing is the most overlooked considerations in selecting a site and in designing an observatory. Don't make this mistake! Even if you are going to build a small structure in your backyard, determine the location that gives the best seeing.

Be sure to construct your observatory with materials that produce the least thermal disruption. It is critical to avoid heat buildup (see Telescope Making #33, page 8). Concrete block and brick buildings absorb heat all day long and radiate it all night long. Asphalt walkways and parking lots next to the observatory are particularly destructive with heat waves coming up for hours. This shimmering in front of the telescope can ruin even low power images. Also, a dome with a small opening which does not allow for ready escape of heat will create a chimney effect at the dome opening.

Roll-off roofs observatories are easier to build than domed observatories. They allow more rapid heat dissipation, and they also allow you to view the entire expanse of the night sky. If you plan to regularly have large groups visit your observatory, remember that only one person can look through the telescope at one time, and only a few persons can crowd around a computer monitor to look at CCD images. It can get rather boring for everyone else standing around in a dark building. With a roll-off roof observatory, while one person is using the telescope, everyone else can enjoy a naked eye view of the sky, scan the sky with binoculars, or even set up another small telescope in the building.

Roll-off roof observatories, however, suffer from some serious drawbacks. One of their most significant problems is they offer little wind protection. In addition, they will accumulate water and snow on the roof if it is flat. As they become larger than 10 feet square, they are difficult to construct. Roof support and movement becomes much more difficult.

The Grasslands Observatory has a peaked roof constructed out of a wood frame and beige metal siding. The metal siding covers the entire building. It was used, because it blends in with the natural grass/desert environment, reflects heat, and resists the weather. The roof is peaked to allow for the large size of the telescope, which rises eight feet into the air even in its "resting" position. One advantage of a peaked roof is it resists accumulation of water and snow but is more difficult to build and weighs more.


Construction Problems

There are innumerable articles about how much fun it is to have an observatory and how easy they are to build. "Easy to build" is a relative term. Nothing is easy to build if it is large and at a remote location. Observatories can be easy to build and maintain if they are small, and if you have good mechanical skill or can enlist the aid or those with good mechanical skills.

The design for an observatory depends on one's resources both financial and mechanical. Amateur observatory projects are similar to defense contracts -- they have frequent cost overruns. The Grasslands Observatory cost about twice what was planned. No matter how well you think you have your observatory budget calculated, take your estimated cost, double it and add 50% more to arrive at a realistic value for your actual expenses. The larger the observatory and the more remote it is, the more likely there are to be construction problems and cost overruns.

Remote Sites

If you finally decide to build an observatory out of town at a truly dark site, the first problem you will encounter is finding an affordable piece of land. In most parts of the country, a tract of land with dark skies, unobstructed horizons, good access roads, privacy, and full utilities (electricity, water, and phone) is hard to find at any price, especially if you do not want to drive more than an hour to the site. This is especially true in the relatively unpopulated West. Much of the land is owned by federal and state governments. Rural land is nowhere as inexpensive as city dwellers imagine. Even raw desert is expensive - land within 60 miles of Tucson costs on the order of $2000-10,000 per acre or more. Typically, you must pay cash for the land, and it may not have a good access road or utilities.

Hidden Costs and Other Aggravations and Risks

There are many "hidden" land and construction costs beyond the initial purchase price: taxes, fencing, building permits... The taxes for the twenty acre Grasslands site were once almost $1000 a year. They would skyrocket if there were "improvements" such as a house or mobile home. It is wise to become familiar with the zoning regulations in your area. For example, mobile homes are not allowed in the county where the Grasslands Observatory is located. In some municipalities or neighborhoods, an observatory might not be allowed. Check beforehand. Be sure to obtain appropriate building permits; otherwise, you will be sure to later have an unpleasant encounter with city or county authorities. In an extreme case, you might be fined and made to remove your observatory!

It is not uncommon for a club to be given an observatory site by a local benefactor or government entity. If the club actually owns the land and is free to do with it whatever it likes, this is a splendid situation. Someday, if light pollution brightens the skies because of growth in the area, the land has probably increased in value and can be sold for a profit. In this case, the club can use its profits to relocate its observatory. Even though this might not be easy, it could be preferable to having a large telescope rendered worthless by intolerable light pollution.

There are, unfortunately, many sad stories of amateur organizations building marvelous observatory complexes in a park at the edge of town. When the site was chosen, it was dark, and the club was allowed to use it for free. Twenty years later the park is surrounded by the city which has grown out past it. Now, the site is no longer dark. Since the club doesn't own the land and never acquired any "equity" in it, the club can't afford to move its telescopes to a darker site. When buying land and especially when leasing a site at a very low price, you must allow for future growth in the area. What may be dark skies today could be bright tomorrow.

The Grasslands site came with no electricity, phone, or water, and it still has no running water. Over the years, phone service and electricity have been installed. Before power was brought to the observatory, electricity came from a 6000 watt generator. You do not need this much power to run a telescope, but you do need considerable power to run a computer and CCD as well as lights and power tools. Telescope operation, even for the largest of telescopes, only requires battery supplied power. A portable car battery or Porta Pac work quite fine. If you want to have a reading light, a hot plate, or a computer, then at least a 500 watt generator will be necessary.

Is there any water in your area? It could easily run $10,000 or more to put in a well. Telephone service in a remote area may be next to impossible to obtain. Consider a CB radio or cellular telephone for emergencies and always let someone know where you are going and when you will return. You really don't need to have water, electricity, plumbing, or a telephone for your observatory, but if you want them, be prepared to pay for their installation. If you can't afford their cost, plan sensibly for reasonable substitutes, such as plenty of toilet paper, transportable water, a generator, and a CB radio.

Generators need to be run at full load; otherwise, they tend to become "gummed up" and run poorly or not at all. Over the years, the Grasslands Observatory went through approximately four different generators due an assortment of problems. A 500 watt generator is reasonably quiet if it sits away from your observing area. Unfortunately, a 6000 watt generator is very loud and requires the full strength of two persons to lift it into the back of a truck to transport it to a repair facility.

The Grasslands generator was put in a specially built generator building/small storage shed 50 feet north of the observatory. The shed was insulated to trap sound, and underground conduit ran from it to multiple outlets in the observatory, enabling one to easily find a place to plug in a power tool, lamp, or a piece of telescope equipment. By the way, you can never have enough electrical outlets. When designing an observatory, plan for as many electrical outlets as possible. Inevitably, you are going to have to repair something in a very dark, inaccessible spot late at night. Being able to plug in a spotlight and use a power tool because of a nearby outlet, is much preferred to working with one hand and trying to point a flashlight with the other hand.

After power was installed at the Grasslands Observatory, the generator was given away, and the generator shed abandoned. It because a jump heap, and bees set up a large hive in it necessitating the services of a professional bee keeper to remove the bees. They did leave behind a lot of delicious wild honey. In late 2013 and early 2014, a large addition and storage room were added to the Grasslands Observatory Control Buiding. The old generator shed was completely removed, and the area cleaned up.

It is important to protect your observatory from idle trespassers, human and otherwise. A good fence, strong locks, and a good insurance policy are highly recommended. To paraphrase Robert Frost, a fence is a way to preserve good neighbors. Cattle are a particular nuisance in Arizona. In this state, land designated "open range" means cattle and horses have the right to graze wherever they want. It is up to you to fence them out. These animals are very hard on buildings. They love to rub against any free standing structure, such as the edge of an observatory. They can demolish the sturdiest of buildings in no time. They eat decorative landscaping, and they leave rather large droppings.

To prevent all these problems, the Grasslands 20 acre site was surrounded by a barbed wire fence. Twenty acres is not a lot of land until you have to pay for it or fence it. Because we had no previous cowboy experience, it took us five weekends in the hot July and August Sun to fence the property. Our sufferings included mosquitoes, summer thunderstorms, mud, blisters, cuts, sore muscles, and the less than gentle cajoling of the local cowboy we hired to direct the fencing project. This experience taught us much more about barbed wire than we ever wanted to know and cost $1000 in material and labor expenses.

Cattle have proven to be somewhat of a blessing for the observatory, however. A local rancher has contracted to use the land and hundreds of acres of surrounding land to graze his cows. Approximately half the time there are 6 to 10 cows grazing on the observatory property. This reduces the land taxes to less than $10 a year, because the land is being used for cattle grazing, an activity favored by the laws of Arizona. The cattle actually help keep the native grass from growing out of control and reduce the risk of grass fires. The rancher is careful not to overgraze the land and actually pays a small monthly grazing fee for use of the land. An additional fence was erected around the observatory building itself to protect it from the cattle, and the gates on the property have to be kept closed at all times to prevent cattle from getting loose.

Domes usually offer much better wind protection than other types of roofs, but the dome has to ride on a perfectly circular rolling surface. Even golf balls will work as roller bearings if there is an excellent fit between the roof and its track. If the dome is heavy and not well fitted to its track, it will be quite difficult to move. The weight and fit for a roll-off roof are just as critical. The Grasslands Observatory proved this point the hard way.


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