Sunrise And Sunset

We want the Home Control System (HCS) to be know when sunset and sunrise is meant to be so that it can validate the detected dawn and dusk times using the twilight sensor.

This site shows how you can use a well defined algorithm to predict sunrise and sunset times, knowing your location, the date and current timezone. I've used a java implementation of this algorithm to enable this, though I did have to modify the code slightly to get it to fit my purpose.