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

 

BACK