Cardboard Tube/Truss Tube
Advantages Disadvantages The Cardboard Tube Block street lights and Moon light.
Keeps sticky fingers from the mirror.
Delays dewing of the mirrors by blocking radiation to the cold sky.
Traps heat waves from the mirror so they must remain in the light path. The Truss Tube Heat waves from the telescope structure drift away from the light path. Stray light and sticky fingers have access.
If humidity is high the telescope mirrors dew up quickly if exposed to the night sky.
Nothing / Dome / Roll Off Roof
Advantages Disadvantages Nothing Costs nothing.
Allows people to gather around the telescope or form a line to wait for viewing.
Not good in the rain. Roll off Roof If many people are waiting their body heat will dissipate easily. If it is humid dew will wet the equipment. Dome Only a small slit is exposed to the cold sky. Equipment in the dome stays at the air temperature and not the sky temperature. Heat in the dome will escape through the dome slit in front of the light path.
The dome must be repositioned when the telescope is repositioned.
Masonry Observatories / Insulated Observatories
Advantages Disadvantages Masonry Observatories Tend to be fireproof Heat waves from the masonry spoil the view until a few hours before dawn. Insulated Observatories Can be refrigerated to the night air temperature during the daytime so the equipment and telescope will be ready for use at the end of dusk. None
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