your application is a great tool and I like the UI and that no additional SW is needed (unlike TPE)
Please also look at TPE (Adobe AIR based, http://stephentrainor.com/tools )
Your tools is easier to use, especially if you add a bar to quickly scroll through the days/weeks of a year (already suggested
To me the ACCURATE numbers of Alt/Az are important -- maybe have a pop-up window showing those values (as others have suggested already)