In this example, we set register #11 half hour before sunset, and clear it half hour after sunrise. Our hardware configuration determined that register #11 is allocated to Relay 3, which we have wired to control the parking lot lights. Register #12, Relay 4, shows how to do it the old way using time of day.
The above example shows two scheduled events that will happen every day of the week because all days are checked. If you wish the weekly event to only occur on Saturday, for example, you would only check the "S" box at the end of the string of boxes. For weekdays only, you would check M through F (Monday through Friday).
The astronomical clock requires knowing where in the world you are. The clock setting page found at System->Setup->Time & Date includes a section for setting location.

Once the internal battery backed clock and calendar have been set, and you have entered lattitude, longitude, and time zone, the clock setting page will show you when the system has calculated sunrise and sunset to be at this location.