A solstice is an astronomical event that occurs twice each year when the Sun reaches its highest or lowest point in the sky. In the Northern Hemisphere, June 20th is usually the longest day of the year and is known as the summer solstice. At Puerco Pueblo, sunlight from the rising summer solstice Sun flows down a cleft in a boulder, and the changing light and shadow on a spiral petroglyph shift as the Sun rises and moves across the sky. Between June 14th and 28th, a shaft of light moves down the side of an adjacent boulder until it touches the center of the spiral within a few minutes of 9:00 am, and the full interaction takes about an hour. Prehistoric peoples used solar calendars to organize life around the changing seasons, including planting crops and anticipating summer rains, and solstice days marked key points in the seasonal calendar and annual ceremonial cycles. This significance continues in the ceremonial calendars of contemporary indigenous communities, where the summer and winter solstices divide the year in two. In Petrified Forest National Park, researchers have identified more than a dozen calendric petroglyph sites, and many more exist throughout the Southwest, reflecting the importance of marking seasonal change to prehistoric peoples and their descendants.
