Re: [ATM] How to test a mirror blank?

[David Nicholls <dcn@dcnicholls.com>]

Dale Eason wrote:
> That may work, however I once pointed an IR
> thermometer at the sun and was surpirsed to discover
> that it was about 65 deg F on a warm summer day.  That
> is when I realized that the sun emits very little IR I
> think the sun emits much higher frequency radiation. 
> What I was measuring was the sky temp.
> 
> Dale Eason

The sun does put out a lot of IR, but it's only 1/2 a degree wide, 
probably less than your thermometer view angle.  The radiation 
temperature of a clear sky is typically 20 deg C (36 deg F) lower than 
the ambient air temperature.

The H2O and CO2 absorption bands take big bites out of the solar IR 
spectrum, so you'd be viewing the middle atmosphere temperature for some 
parts of the IR spectrum.  Not a simple problem!

DN


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