> I also don't think they control the temperatures of the mirrors but I am not sure about that. I know they typically air-condition telescopes during the day t

> I also don't think they control the temperatures of the mirrors but I am not sure about that. I know they typically air-condition telescopes during the day to keep the mirror at the anticipated nighttime air temperature, to avoid convection currents caused by a warm mirror. That requirement would seem to preclude controlling the temperature to a specific value, I think.