In article ,
"Martin X. Moleski, SJ" wrote:

On Fri, 11 Feb 2005 15:12:27 GMT, George Patterson
wrote:

W P Dixon wrote:

That's pretty cool (Pardon the pun ) Where can I read up on that George?

I read about it in the 70s and don't remember where; probably a Science Fact
article in Analog or Popular Mechanics. As I recall, the technique is to dig
a
hole large enough to keep your water container completely below ground.
Cover it
during the day and insulate it (the Romans used straw). Leave it open to the
night sky. It will freeze in a few days. The article said it only works in
areas
where the night sky is usually perfectly clear (ie. the desert).

This site gives a reference:

http://www.madsci.org/posts/archives/nov99/941723540.Sh.r.html

Marty

Except that particular reference isn't very clear about the relative
roles of heat transfer to the air (and into the surrounding ground) and
radiative transfer to the sky -- e.g., it says

". . . at night, the pit would be uncovered so that it could lose
heat to the desert air."

You might take that to imply that the air temp in those African and
Palestinian deserts goes below 32 F at night? (Anyone know?)

You guys are into some interesting physics here. Do the plane wings
frost even when the surrounding air is above 32 F because their net heat
transfer to the surrounding above-freezing air is not as strong as their
net radiative heat transfer to the cold sky? (which should also imply
equally strong net heat connectivity to the ground below, is that not
so?)

Or do they acquire and retain frost because some colder and therefore
heavier below-freezing air just fell down on them at some earlier time?

I'll wait for an authoritative answer, but bet on the latter explanation.