Times of Sunset at Topanga, California
June 21, 2010
As the Earth orbits the Sun, the 23.5 degrees tilt of its spin axis relative to its orbital plane causes the azimuth of sunrise and sunset to vary. At the extremes – summer and winter solstice – the sunset azimuths occur at their most northerly and southerly positions, respectively. This picture shows a composite of three photographs taken near Los Angeles, California (latitude about 34 degrees) on the two solstices and the equinox between them. The sunset azimuth changes by about 57 degrees, typical for mid latitudes. On the equator, the azimuthal range is only 47 degrees, while at the Arctic or Antarctic Circle, it's 180 degrees. True sunset occurs when the solar elevation is zero degrees. In the mountains; however, the local horizon is actually a few degrees above the true horizon. Since the Sun doesn't set straight down but rather moves northward as it approaches the horizon, the azimuth of the equinox sunset on the local horizon is a bit south of 270 degrees. The equinox sunset on the true horizon falls at 270 degrees.