Whoa Jones! If the sky can be considered a cold dome, and if frigorific radiation follows the rules of geometric optics then when an elliptical reflector is pointed at the sky this is similar to placing a cold body at the reflector's near focus F1. The cooling rays that happen to pass through this point will be directed towards the thermometer at the far focus F2. This thermometer should cool roughly half as much as a thermometer placed at F1. If it is substantially less than half then ordinary radiant cooling would be sufficient to account for the difference.
This link shows how an elliptical reflector or a hyperbolic reflector could be used. The key thing to remember is that cooling rays are being emitted in all directions from the sky, but the reflectors selectively focus those rays which happen to pass through F1 in the case of the elliptical reflector or would have passed through F1 in the case of the hyperbolic reflector. https://drive.google.com/file/d/1eT1hmvt-QLpdv0ORoLcaFwewI8Qbhpz6/view?usp=sharing The extra elements refer to some of the events, images and ideas that I contemplated concurrently with this topic. ;-) Harry On Fri, Jan 21, 2022 at 1:42 PM Jones Beene <jone...@pacbell.net> wrote: > > Of interest: > > https://www.researchgate.net/publication/262806145_Blue_Sky_Cooling_for_Parabolic_Trough_Plants >
