> You can prove to yourself that radiation can cause cooling in a practical
> way.  Take an old soup bowl, paint the inside black, and fill with water
to
> about 5-10mm of the top.  Insulate the outside of the bowl well and cover
> the top with a layer of plastic wrap to make a layer of still air above
the
> water.  Set this outside overnight with a clear view of the sky.  The
water
> can freeze under the right conditions without the air temperature ever
> dropping to the freezing point.  This works only when the sky is clear
> because the water is radiating its heat to the sky but very little is
coming
> back.  Try it yourself.  You will have to wait a while for the right
> weather, especially considering the heat wave we've been having around
here
> the last few days.  Some of the folks in the southern hemisphere or at
high
> altitudes could do it this time of year.


AFAIK the "ancient" Romans & Egyptians used to make ice by this method.


        RM

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