After some searching, I finally found a website that can calculate the sun's zenith. Just look up your city's lat/long (remember, west/south are negative even if it doesn't show where you look up the lat/long) and the time of sunrise/sunset and use this site:You have to enter in the sunrise/sunset times separately, but it works.San Diego is:Lat: 32.73Long: -117.17Sunrise Z.: 90.7379Sunset Z.: 90.8880