On Tue, 27 Sep 2011 19:28:58 -0700, Jeff Liebermann
wrote:

http://en.wikipedia.org/wiki/Solar_variation
It doesn't explain everything, but is a substantial part of the
puzzle.
http://www.ucar.edu/news/releases/2006/brightness.shtml

NASA's Glory satellite was suppose to measure all this more accurately
as the exact effect of variations in solar output isn't totally clear.
However, the satellite failed to reach orbit.
http://glory.gsfc.nasa.gov/misison_details.html
http://en.wikipedia.org/wiki/Glory_(satellite)

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558