My question about the shadow has to do with earth tides. Are you certain that this is NOT what you are observing? Oklahoma U has done some credible work on this, (unless somebody else here knows different, which I would rapidly listen to) and this is the web site for some of the work I have seen. An earth tide would very slightly change the shadow, yes? I am trying to help, not hinder your work Shan...

glen

http://www.okgeosurvey1.gov/tide.html