Astronomical cupolas & thermal equilibrium

[JeffOCA]

Hi,

In astronomical observatories, the cupolas and their building walls are painted in white in order to reflect sunlight and not absorb too much warmth during the day. This minimizes the difference between internal and external difference when night falls.

However, in some observatories there are aeration gaps above the cupola. What for ?
If the cupola and its interior are heated by daylight, the gaps are useful to requilibrate the int. and ext. temperature at the beginng of the night.
But, during the day, these gaps are not efficient : warmed air from the outside enters the cupola where the air is colder.

Am I wrong ?

Other point : in some observatories the cupolas are green instead of white. Why ? Is it due to an oxydation of Cu ?

Thanks for answering.
JF

 

[JeffOCA]

No one ?

 

[JeffOCA]

Anyone ?

 

[twofish-quant]

In astronomical observatories, the cupolas and their building walls are painted in white in order to reflect sunlight and not absorb too much warmth during the day. This minimizes the difference between internal and external difference when night falls.

It's not so much the temperature difference that kills you, but rather the air currents that get generated by the hot material.

But, during the day, these gaps are not efficient : warmed air from the outside enters the cupola where the air is colder.

Hot air rises so if you have a hole in the ceiling, the hot air won't come in.

Other point : in some observatories the cupolas are green instead of white. Why ? Is it due to an oxydation of Cu ?

Hmmmm... I did some googling, and found this paper on observatory construction...

http://tfa.cfht.hawaii.edu/papers/springer-tfa-paper.pdf

In section 2.1, they mention that they had to paint the dome green/gray because the Bureau of Land Management didn't want the observatory to spoil the view of the forest.

 

[JeffOCA]

Thanks !