Astronomical cupolas & thermal equilibrium

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Discussion Overview

The discussion revolves around the design and thermal management of cupolas in astronomical observatories, focusing on their color choices, aeration gaps, and the implications for temperature regulation during day and night. The conversation touches on both theoretical aspects and practical considerations in observatory construction.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant notes that cupolas and walls are painted white to reflect sunlight and minimize internal-external temperature differences at night.
  • Another participant suggests that aeration gaps above the cupola may help equilibrate temperatures at night but questions their efficiency during the day when warmer outside air enters.
  • There is a claim that air currents generated by temperature differences can be problematic, rather than just the temperature difference itself.
  • A participant mentions that hot air rises, implying that a ceiling hole would not allow hot air to enter effectively.
  • Questions are raised about the green color of some cupolas, with one participant suggesting it may be due to copper oxidation, while another references a paper indicating that green/gray paint was chosen to avoid spoiling the natural view.

Areas of Agreement / Disagreement

Participants express differing views on the effectiveness of aeration gaps and the implications of temperature differences, indicating that multiple competing perspectives remain unresolved.

Contextual Notes

The discussion includes assumptions about thermal dynamics and the specific environmental conditions affecting observatories, which may not be universally applicable. The reference to external sources introduces additional context but does not resolve the questions raised.

JeffOCA
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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
 
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JeffOCA said:
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.
 
Thanks !