Arduino library to compute sunrise / sundown times based on geographic location and current time with a reasonable compromise between accuracy and computational effort. In most cases the computed times will differ by a few minutes only which should be sufficient for most applications. Use of this library is targetet at e.g. outside illumination timers.
The formula used here is based on what I learnde from the following link (in German only, but google translate is your friend):
http://lexikon.astronomie.info/zeitgleichung/
There is basic support for some date calculation that will compute the day of year for a given day/month/year as well as a list of coordinates for some major cites in the world.
Included is also a cron like scheduler that can "run in the background" (with regular calls to a handle() method) and will call a virtual method every minute and update sunrise/sundown times whenever a new day starts.