There is another interesting iPhone APP for photographers called "The Photographers Ephemeris" or TPE. It allows you to calculate sun and moon rise and set times and even track the position/azimuth of the sun/moon for any day/time/location on earth. It can even determine when the sun will dip behind a hill etc. Very helpful to us for whom light is so important. I think it just a couple of bucks but it has saved me a lot of time and frustration.