Sunset From Fort Mandan

his image illustrates the location of sunset at equinox (March 21 and September 21 ) and solstice (June 21 and December 21). During the time intervals between these dates, sunset falls between the marked positions on the western horizon. An angular error of 35 degrees will produce a direction error of 7 miles north or south of true west for every 10 miles traveled in a westerly direction.

--John Logan Allen