Seasonal Motion

The locations on the horizon where the Sun rises and sets changes in a repeating pattern. The height of the midday Sun in the sky changes along with that same pattern. The length of time the Sun spends in the sky also changes with this pattern. We call this repeating pattern the cycle of the seasons.

As viewed from the northern hemisphere of Earth, on the first day of spring, the Sun rises directly in the east, spends 12 hours in the sky and sets directly in the west. In the height of summer, the Sun rises in the northeast, spends the longest time in the sky, and sets in the northwest. On the first day of autumn, the Sun rises directly in the east again, spends 12 hours in the sky, and sets directly in the west. In the depths of winter, the Sun rises in the southeast, spends the least amount of time in the sky, and sets in the southwest. The cycle then completes with a return to spring. The experience of the seasons is reversed for the southern hemisphere of Earth. When it is summer for Europe it is winter for Australia. When it is winter for North America it is summer for South America.

During this cycle another changing pattern is where amongst the stars the Sun can be seen, and which constellations of stars are visible at night. All of these changes are caused by Earth’s orbit around the Sun. It takes one year for the Earth to complete one trip around the Sun. The direction in space where the night side of Earth points changes with this motion, which changes when during the day different constellations can be seen. 

Also, the direction in space where Earth’s north pole points is not aligned with Earth’s orbit around the Sun. We call this Earth’s tilt. The tilt stays pointed in the same direction in space while Earth orbits the Sun. This makes Earth’s north pole change its orientation to the Sun during a year and causes all of the seasonal variations we observe. 




sunlight through doorway of building
The Temple of the Sun is aligned so that on the equinoxes, the sun will project itself through both door jambs, eastern and western facing, and shine through to the population that would have been awaiting this event, along with an announcement from the priest, from the plaza below. On the other calendrical extremes, the solstices, the sun, when shining through the south/north facing doorways respectively, casts a shadow on the frame of the west/east facing windows. By charting the sun's movement through the architecture of the building, priests were able to keep track of the solar cycle, predicting equinoxes and solstices, and thus orienting the people to an agricultural and sacred calendar. (Image Credit: Jim Spadaccini, Ideum)
stone pyramid with shadows
Descent of K’uk’ulkan - Equinoxes. The serpent descends the north stairway of the Castillo on the spring equinox. Thousands gather to witness the event. (Image Credit: Jim Spadaccini, Ideum)
a diagram showing that the tilt of Earth's spin axis remains the same on either side of Earth's orbit and results in different illumination across the globe.
The tilt of Earth's axis points in the same direction throughout its orbit. The solstices happen when the Sun is seen directly above the most northern or southern locations on the planet (the tropics). Image Credit: B. Mendez
The Sun's path in the sky during solstices and equinoxes is traced out in this image.
As seen from 40 degrees north latitude, the path of the Sun in the sky is lowest and shortest on the winter solstice. The Sun rises in the east and sets in the west on the equinoxes. On the summer solstice, the Sun's path is the highest and longest. Image Credit: B. Mendez/Stellarium