Position of the Setting Sun
August 26, 2014
Summary Author: Randall Scholten
This series of photos shows the progression of the point of sunset as it occurs on the western horizon at Port Orford, Oregon. The photos were taken on three consecutive nights (August 7-9, 2014) looking out across the Pacific Ocean toward the islands and rocks of the Orford Reef. These islands are 5 mi (8 km) from shore. The island on the right is Arch Rock.
At this time of year and from this location, the Sun sets at approximately 293 degrees, and 0.4 degrees farther south every day and 1 minute and 20 seconds sooner. This change will increase as the autumnal equinox gets closer (September 23). Then the point at which the Sun sets (270 degrees) will change by .53 degrees, and will be 1 minute and 47 seconds earlier.
During the solstices, when the direction of movement of the sunset’s location reverses, there's very little movement of that point and very little change in the length of day. The inclination of the Earth's rotation axis causes the position of sunset and sunrise to change every day. The maximum angular distance between two sunsets is the angle between two solstices. This angle changes with the latitude of the location. It's minimum at the equator (where it's equal to twice the ecliptic obliquity). After that the angle increases according to the absolute value of the latitude until it causes the midnight Sun in polar areas.
Photo details: Nikon D810 camera; 1/125 sec. exposure; f/6.3; ISO 200; sigma 50-500 mm - f/4.0-6.3 zoom lens at 500 mm. Source of azimuth, sunset times: SunEarthTools.com.