Extending Roger Bailey's treatment, if you know the time and direction of sunrise you can easily estimate the time and direction of sunset, or vice-versa:
Time of sunset = 24 - (time of sunrise) Azimuths of sunrise and sunset are equidistant from the North-South meridian, remembering that sunrise is east and sunset west of the meridian. If you know the direction of sunrise or sunset at a given solar declination D degrees North, you can easily estimate the time and direction of sunset or sunrise at declination D degrees South: Time of sunrise at D degrees South = 24 - (time of sunset at D degrees North) Azimuths of sunrise at D degrees South and sunset at D degrees North are equidistant from the East-West line, remembering that in the Northern hemisphere the former is South and the latter North of the East-West line. You can interchange "sunrise" and "sunset" in these expressions. If you have a vertical declining sundial with declination lines and a horizon line, you have all the data you need to use the above information. John Lynes Roger Bailey wrote - The times of sunrise and sunset can be easily determined on a vertical declining dial that has declination lines. The horizontal line from the base of the gnomon is the horizon line. The intersection of the declination line and the horizon line shows the time of sunrise or set. This is of limited use on south facing dials as the scale of the gnomon and resulting declination lines is usually to great to show much more than the winter solstice.
