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ABSTRACT
The design and construction of the observatory pier, dome,
and control room for a small college observatory is discussed.
This includes a suggested floor plan, elevation plan, control
room location, traffic flow patterns, and other factors. These
criteria are discussed in respect to how they affect the efficiency
of using the observatory for student use, research use, and
for public nights.
The required performance of the telescope, instruments,
and related auxiliary equipment is considered.
INTRODUCTION
 Many
observatories are designed ignoring the actual use of the
telescope.
With over 30 years of experience in small college observatory
design and telescope manufacturing, we will discuss telescope
access, visitor flow, and optimal seeing conditions as well
as considerations for structural techniques, materials implementation
and practical applications in the design process.
The observatory and telescope will be used for education,
training of students to use research telescopes and instruments,
public outreach, and for public visitors.
GENERAL PIER
CONSIDERATIONS
 An
isolated concrete pier running all the way from a suitable
footing below grade to the sole plate of the telescope pedestal
is the best solution. Isolation must be maintained.
This includes any conduits between the building and the pier.
The pier needs to be offset to the south the proper amount.
Rarely will the pier be in the middle of the dome.
 The
height of the pier affects the convenience of using the telescope.
For enlarged versions, click on drawings or links below:
Pier Location or Placement
The pier is normally offset to the South of the dome center
line (in the Northern hemisphere). The pier needs to be centered
East to West and the rotational alignment of the pier and
the pier bolts MUST be TRUE North-South (Celestial North).
 The
pier height is relative to the dome horizon line and should
be set to allow an unobstructed telescope horizon at 7 to
10 degrees above the horizon.
 In
order to provide vibration isolation, there should be adequate
clearance allowed between the pier and the floor.
Also, provide vibration isolation between building machinery
and the floor so as to minimize vibrations induced into the
building. Locate building machinery as far away from the pier
as possible.
Provide separate foundations or footings for the pier and
for the dome walls.
The telescope manufacturer must supply a “Pier and
Dome Requirements” drawing showing the pier offset and
height relative to the dome horizon line and the recommended
observing floor height. 
NOTE: It is imperative that the institute’s person
in charge of the new observatory check the azimuth alignment
before proceeding with project development.
It is more than likely that the building contractor will
be unaware of the significance of this critical alignment.
Pier Construction
 Most
often the pier is made from reinforced concrete. A large footing
is poured with a column coming up from the footing.
The upper part of the column can be hollowed out to reduce
the moment of inertia and the thermal mass.
Steel piers can be made, but they tend to be much more expensive
than concrete.
 An
offset can be built into a steel pier to transition from a
concrete footing or column to the sole plate for the telescope.
A pier running from a footing well below grade is much better
than using the structure of the building.
In general, buildings constructed from concrete (slab on
columns and beams) are much stiffer than steel framed buildings
and many observatories have been successfully built using
the building structure rather than a separate pier.
Many observatories have been less than successful when using
the building structure of a steel building.
Pier Structure
 NOTE:
The important deflections are NOT the translations, but are
the top end rotations of the pier and the torsion of the pier.
This is because the telescope is looking at an object at
a distance of infinity. If the telescope simply translates,
the image does not move in the field of view.
Any rotation does produce image motion. Motions as small
as 0.1 arc second are detectable.
1. The Tip-Tilt and rotation in azimuth stiffness must be
very high
a. For a load applied to the eyepiece, the stiffness
needs to be 30 lbf per arc second or stiffer.
b. Resulting torsional stiffness of the pier
needs to be 30-lbf-ft per arc second (azimuth stiffness).
 2.
Natural frequency with telescope installed should be greater
than 30 Hz.
3. The South bolt typically has a considerable upward directed
force.
4. Concrete material should be used because it has some internal
damping.
5. Adding damping is difficult due to the very small amplitudes
involved.
Pier Vibrations
 Seismic
vibrations will couple into the telescope pier. Nothing can
be done to mitigate these. Fortunately, seismic vibrations
are small and don't occur often enough to affect the telescope.
Building vibrations from Heating, Ventilating, Air Conditioning
(HVAC) machinery are a major concern.
Most buildings support the HVAC machinery with vibration
isolators, but then defeat the isolation by using rigid electrical
conduits.
 Vibrations
from the building elevators may also couple into the pier.
Even the dome rotation can couple into the telescope.
The problem comes from supporting the telescope from the
building structure and not an independent, isolated pier.
Other Pier Considerations
 Large
diameter conduits are usually run through the pier to provide
cable runs. Optimally, the pier should provide multiple large
conduits for telescope and instrumentation wiring.
This would include at least 4 inch diameter conduits with
outlets and inlets in convenient places.
It is not possible to have too many or too large of conduits
for telescope instrument control cables. Insulating the outside
surfaces of the pier immediately below the telescope will
help mitigate thermal mass concerns.
Conduits exiting the pier must be cut so there is an air
gap so the conduits will not conduct vibrations from the building
into the pier.
OBSERVATORY
CONSTRUCTION AND PLANNING
 To
achieve good seeing, the observatory needs to be operated
at the outside air ambient temperature.
This requires minimum heat generation, good ventilation,
insulation, and low thermal mass construction.
It is important to plan thoroughly in achieving an optimal
observatory.
Additionally, considerations for floor space planning, visitor
access, handicapped access, visitor flow and safety, lighting,
power, future expansion of instrumentation, communications
and maintenance must all be adequately be addressed.
Observatory Floor
Layout
 The
observatory should be designed to be operated from an air
conditioned control room. Auxiliary controls can be provided
to operate the telescope from the observing floor. Also, the
observatory floor should be of low thermal mass.
The prime working space is the quadrant to the North of the
telescope whereas East and West quadrants are less used floor
space.
The height of the observing floor relative to the telescope
should be set for comfortable viewing. For an observatory
that is used for the public, this height is important. The
proper value depends upon the size and configuration of the
telescope and the intended users (children would benefit from
a higher floor height, for example).
The observatory floor may require a hatch to allow lowering
the primary mirror in its crate to a lower level with access
to a loading dock as the telescope mirrors will require periodic
cleaning and re aluminizing.
Also, the floor may require a flush mounted lift table for
handling large instruments and the primary mirror and its
cell.
Access to the Observing
Floor
  For
small and moderate size telescopes, the observing floor height
will usually not allow a full size door between the floor
and the ring beam that supports the dome.
Entry to the dome using a full size door will be at a lower
level than the observing floor requiring some steps up to
get to the floor.
These steps should be located in the South-West or the South-East.
Usually the steps can’t be located in the South because
they would interfere with the pier. Sturdy handrails are needed
at the stairwell.
 Entry
into a dome housing a small to moderate telescope will require
a small landing and then steps up to the observing floor.
 Entry
from the South is preferred with the steps spiraling up along
either the South Eastern or South Western quadrants of the
dome walls.
The upper end of the stairs will terminate near the West
or East quadrant.
In either case, when entering the observing floor area, an
air lock consisting of a short corridor with two doors is
essential.
The observatory must provide for easy access to move the
primary mirror and cell into and out of the observatory. This
may require a hatch in the observing floor and a suitable
hoist.
These are a few safety and practical suggestions for observatory
floor access:
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Do not use a short height door to enter the observatory.
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Do not use a tight spiral staircase.
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Do not use a stairway through a trapdoor or a hatch.
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Incorporate a plan for an alternate exit to the roof
or to the outdoors.
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Insure that emergency exits are not blocked.
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If the exit is to the roof, then roof safety measures
must be taken.
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All exits need appropriate lighting (downward directed,
red, etc.).
Handicapped Access
 
Many observatories have a requirement for handicapped access
to satisfy the Americans with Disabilities Act (ADA).
Some observatories have wheelchair lifts that allow access
to the observing floor.
 Only
a few observatories actually meet the ADA requirements by
providing handicapped access to the telescope eyepiece.
 DFM
Engineering, Inc. offers an Articulated
Relay Eyepiece™ model ARE-125™.
It allows true handicapped access to the telescope.
A person seated in a wheel chair may simply pick up the eyepiece
and bring it to their eye for convenient viewing regardless
of telescope position.
The images here show several wheelchair lifts that can be
used at an observatory to provide access to the observatory
floor.
Dome Lighting,
Power and Communications
White and red lights are needed throughout the observatory,
stairways, and safety exit walkways.
White lights allow working on the telescope and instruments.
Red lights are needed when operating the telescope particularly
during public nights.
All lights must be on dimmers. Provide many duplex power
outlets on the dome walls for instruments and auxiliary equipment
using several separate circuits.
A telephone with sufficient cord to reach to the telescope
is needed to allow communications when working on the telescope
or instruments. Provide wiring or fiber for high speed data
communications (e.g.. CAT5e or Cat6 cables).
Ventilation
and Thermal Control
 Minimum
heat generation is provided by moving as much of the electronics
and people out of the dome as possible and placing these items
in the control room.
A telescope can be made that dissipates less than 20 watts
while a person at rest dissipates about 150 to 200 watts,
so the primary heat source during observations can be the
observers.
At a major observatory, equipment heat generation can be
the largest source of heat.
 In
some climates, air conditioning and/or dehumidifying of the
observatory can be beneficial. To improve the seeing, many
major observatories air condition the telescope primary mirror
because the mirror has a large thermal mass.
The optimal temperature of the telescope and the inside of
the observatory should be the expected night time seeing temperature.
 Powered
or forced air ventilation should be provided. The amount of
airflow should be equal or greater than 3 telescope and observatory
masses per hour.
The telescope can weigh 4000 pounds (20,000 Newtons) and
a concrete floor can weigh twice this amount. The building
walls and other structure can also be very massive.
This is why the observatory should be made with metal sided,
steel type construction and the floor should be wood or aluminum.
Concrete/brick construction should be avoided.
With
a low mass construction, the total mass can still be 5 tons
requiring about 7,000 cfm (cubic feet/minute) of air flow.
A typical 20-inch window box fan flows over 4000 cfm with
no restriction, so the ventilation can be provided by a relatively
modest fan or fans. Wind produces excellent ventilation if
entry and exit areas are correct.
The flow should suck air in through the dome slit and exit
near the base of the observatory walls-preferably down wind
and across the floor.
The
air should be discharged down wind and in a broad, diffused
manner. This usually requires different fans, so the observer
can choose which way to diffuse the air.
Locate the building vents and heat discharges as far away
from the observatory as possible. They should be down wind
(for prevailing winds, anyway).
All vents should be as diffused as possible. The building
vents could be located to the North as this part of the sky
is not a prime observing area.
 Infiltration
is usually not a problem with a modern domed observatory.
However, the dome must be air locked so when the door to the
dome is opened, there is minimal air exchange between any
conditioned building space (including the control room) and
the observatory dome space.
It is essential to prevent warm building air from entering
the observatory and damaging the seeing.
The East, West, and South walls of the dome should be insulated.
The dome walls should be insulated on the inside so they won'
become a major heat source during the night.
While the dome should be insulated, it typically has low
thermal mass and a lot of surface area, so its time constant
is short.
Shelter Comparisons
(Dome or Roll-Off Shelter)
 Inevitably,
a dome is the better choice between the two options both in
cost and weather protection criteria.
Observatory “roll-off-roofs” typically leak when
it rains. This causes an obvious need for a floor drain and
possible dehumidifier considerations.
The roll off roof may provide better seeing because of better
ventilation. This is its only advantage.
In the college environment, the stray light in a roll off
shelter will be a greater problem than for a dome. This type
of shelter provides much less screening from stray light than
the dome option.
A roll off shelter is thought to cost less than a dome. This
is almost always NOT TRUE.
There are always other factors to consider when making this
type of cost comparison.
For example:
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Maintenance of the telescope is complicated because the
telescope is usually stored nearly horizontal.
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The telescope must be moved to the storage position in
order to close the shelter.
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The shelter still needs a control room.
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Personnel safety is not as good as a dome.
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Each roll off shelter is a “one of a kind”,
so inherently has many bugs and inconsistencies.
Observatory domes have been developed over many years and
have been engineered to accommodate the multiple considerations
necessary in order to alleviate viewing distractions.
An observatory dome, as opposed to a roll-off shelter, enables
the viewer to eliminate the focus on the observatory shelter
and instead focus on the observing.
Therefore, a dome is recommended as the preferred shelter
option and as big as you can afford.
CONTROL ROOM
Control Room Location
 The
control room should be located within 125 cable feet of the
telescope pier. The minimum recommended size of the control
room is 100 square feet. 200 square feet or larger is preferred
as the control room will need to accommodated multiple desks
similar to a multi user computer lab atmosphere.
Many observatories place the control room to the north of
the telescope and have a window looking into the observing
area. Typically, the windows are covered with an opaque material
and are seldom used.
Another option is to have an inexpensive closed circuit TV
looking at the telescope with a display. This is less expensive
than the window approach. The control room may be located
at any convenient location and is often located one floor
below the telescope.
Control Room Access
It is nice to have a door going outside from the control
room to where the sky may be checked for clouds, etc.
 The
control room must be air locked so when the door to the dome
is opened, there is minimal air exchange between the control
room and the dome. This provides greater thermal control in
the observatory dome in an effort to keep the observatory
dome at seeing temperature.
Access to the control room should allow for heavy and bulky
instruments to be brought into the room for testing purposes.
Control Room Features
Large conduits should be available between the control room
and the telescope. These should be 4 inches in diameter or
larger. The conduits should be sealed off with foam rubber
to prevent air flow from the control room to the dome.
A telephone with sufficient cord to reach anywhere in the
control room is needed to allow communications when using
the telescope or instruments.
 There
will be at least 4 PC type computers with displays in the
control room. Wiring or fiber for high speed data communications
should be provided as well as a duplex outlet (15 amps) on
a separate circuit for the telescope control system.
Many power outlets along the wall need to be provided.
The control room environment needs to be air conditioned
to an office environment and provide ample desk top area with
cable pass through holes similar to a multi user computer
laboratory.
It needs to be equipped with white and red lights - all on
dimmers with special consideration to additional lighting
needed to illuminate computer keyboards. It is suggested that
a low power overhead track lighting (with dimmers) would offer
sufficient keyboard lighting.
TELESCOPE CHOICE
 Too
often a telescope is chosen with insufficient performance.
The telescope pointing, stiffness, and access should be considered.
The telescope should be the best the institute can afford
to provide that maximum usage when the weather conditions
permit observing.
The observers should not have to fight the telescope, but
the telescope should be easy to use and very reliable so the
observers don't waste the few hours they are in the observatory.
An equatorial fork mount Cassegrain telescope provides easy
access to the eyepiece and instruments with minimum eyepiece
sweep and minimum need for observing ladders.
Required Telescope
Performance Features
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Telescope Required Performance
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Floor height set relative to the telescope for maximum
convenience
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An Articulated Relay Eyepiece provides maximum convenience
for visual use of the telescope and handicapped access
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Efficient GO TO so minimum time is spent finding the
next object
Necessary Instruments
APPENDIX
The meanings of the words “local” and “remote”
have changed during the past few decades.
These words and several others are defined below:
Definition of terms:
Local: Local control means occurring from the control
room. Most modern observatories are now operated from a control
room (or warm room) not located in the same space as the telescope
and instruments. The telescope and instruments are controlled
by the operator interfacing to a computer.
Remote: Remote control means operating away from the
control room. It may mean operating from the observatory floor,
which is often done for public nights, for example. Remote
may also mean operating or observing using dedicated cables
from a distance such as from a planetarium hundreds or a few
thousand feet away.
Far Remote: The proposed meaning of this phrase is
to indicate operating or observing from a distance where dedicated
cables are not used. For example, the observatory could be
controlled over a campus Local Area Network.
Internet Access: The proposed meaning of this phrase is
to indicate operating or observing from a far distance where
the communications between the observatory and the user is
performed over the internet.
Remote Observing: This phrase indicates observing from
a location other than the control room or the observing floor.
Also see Internet Access. This phrase has two distinct operational
modes defined below.
Unattended Remote Observing - Attended Remote Observing:
Remote observing places considerable demands upon the hardware.
If all of these requirements are totally automated, the observing
may be performed without human intervention (Unattended).
If some of these requirements are performed by an attendant,
and some are automated, the observing is combined (Attended).
Robotic Telescope: A robotic telescope accepts commands
from another controller. Most modern professional and many
amateur telescopes may be considered to be robotic.
Robotic Observing: This phrase usually means that the
telescope and its instruments are being commanded to perform
routine observations that have been preprogrammed. Such observations
may be performed attended or unattended.
For additional information, please see the following links:
• Engineering
Articles for the Optimal Telescope
• How
to Buy a Telescope
• Internet
Telescope Performance Requirements
• Comparing
Telescope Drive Technologies
• US
Naval Observatory 1.3M Telescope
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