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.
TABLE I --
UNANTICIPATED OBSERVATORY PROBLEMS
A. COST OVERRUNS
1. Land costs: purchase costs; taxes; insurance; utility
2. Hidden costs: fencing; grading, road improvements; building
permits; well installation.
3. Costs for permanent observatory equipment (see below).
B. DESIGN PROBLEMS
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.
C. EVERYDAY PROBLEMS
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.
II. THE CHOICE BETWEEN OBSERVATORY AVAILABILITY and
OPTIMAL OBSERVING CONDITIONS; DESIGN FOR SEEING
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.
III. CONSTRUCTION PROBLEMS; REMOTE SITES; HIDDEN COSTS
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
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
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
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
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
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.
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.