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From: Henry Spencer <>
Newsgroups: sci.optics,,sci.physics,,
Subject: Re: IR cooling throught IR window to space
Date: Sat, 21 Mar 1998 22:48:41 GMT

In article <>,
Dale Trynor  <> wrote:
> should cool to temperatures of
>air in much a higher level with some help from the cold of actual space
>itself but to a very small amount and only on clear nights...

Yes, this has been known for a long time.  The Romans made ice in the
desert that way:  insulate the container with a thick layer of straw
during the day, expose it to the sky at night (unless it's cloudy),
repeat as necessary.  A clear night sky is very cold.

>But what I
>thought would be most interesting would be is if this could be made to
>work even during daylight...

Nope, too much scattered sunlight.

>...remember being told that if you looked up from a long chimney you could
>even see the stars during the day...

Unfortunately, that's a myth.  The inability to see stars during the day
is not just because the bright light desensitizes the eye (although it
does).  The incoming sunlight scatters off air molecules; a clear daytime
sky really is glowing bluish-white, just like it looks.  It's much
brighter than any normal star.

On the Moon it would work.
Being the last man on the Moon                  |     Henry Spencer
is a very dubious honor. -- Gene Cernan         |

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