Paths of the Rising Sun at the Solstices and Equinoxes

March 20, 2019

SunrisePanorama (1)

March 2019 Viewer's ChoicePhotographer: John Krieger
Summary Author: John Krieger 

Shown above are three different sunrises as viewed from the city of Aliso Viejo in southern California, looking east over Saddleback Valley toward the Santa Ana Mountains in the distance. Saddleback Mountain is visible at the left, with the shorter of the two peaks marking northeast (azimuth 45 degrees) as seen from my viewing location. This composite photo is a blend of three separate time-lapse photographs; one sunrise each at the summer and winter solstices (on the left and right), and one at the fall equinox, with the fall equinox Sun rising due east (azimuth 90 degrees).

The latitude of Aliso Viejo is about 34 degrees N. Notice that as the equinox Sun crosses the horizon, its path in the sky inclines from the vertical by the same angle. You can also see clearly the seasonal variation in the position of the sunrise. The summer Sun rises to the north of east, and heads higher into the sky, while the winter Sun rises to the south of east, and stays lower in the sky, thus changing the duration and intensity of the solar heating. This gives rise to the meteorological seasons.

You can also notice that the Sun's equinox path appears to be a straight line, while the two solstice paths appear to curve slightly outwards. This is due to the Sun’s declination circle in the sky. The Sun’s apparent path through the sky is always circular, but we view the circle from different perspectives in different seasons. At the equinoxes, we view the circle from the inside, from its center, so we perceive it as a line, but in summer and winter we view the circle from the side, so at these times we actually perceive the curve of the circle.

Photo Details: Each sunrise sequence was made by combining a single background photo taken just before sunrise, with multiple subsequent exposures using a solar filter. All photos were taken with a focal length of 25mm. All timing was performed by computer remote control, with filtered photos taken at 8-minute intervals. ISO was set to 100. Exposure times were between 1/600 and 1/125 second for the unfiltered background photos, and between 1/60-1/32 second for the filtered sun photos. I processed the images using PHP scripts that I wrote myself.