Albert,

I've run across a book containing that formula (I'm pretty sure!!)
and many others related to solar energy:

Duffie, John A. & Beckman, William A.; Solar Energy Thermal Processes;
New York, NY: John Wiley & Sons; 1974

I found the book to be widely quoted in the literature. I don't own a
copy, just have checked it out of the library a few times. Perhaps
some kind soul can photocopy the proper pages and mail them to you.


For an on-line calculator version of this see:

   http://solstice.crest.org/staff/ceg/sunangle/index.html

Here's a Windows PC shareware program
   http://www.seanet.com/%7Esme/sun.html

I hope this helps

Steve

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Stephen Brown, Ph.D.
New England Research
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