For several thousand years the early residents of the Southwestst have used rock surfaces as their drawing board. Recent research suggests that some petroglyph sites in Petrified Forest National Park are more than simple drawings - they are in fact solar calendars!
Watch an ancient solar calendar work from June 14th thru 28th at 8:30 a.m.
A circular petroglyph etched on a boulder behind Puerco Pueblo marks the summer solstice. During the sun's morning trek, a shaft of light is projected onto the boulder and travels down the side to penetrate the center of the circle.
If you were to watch the sun rise and set over a long period of time, you would notice that the sun follows different paths throughout the year. In the summer it rises in the northeast and in the winter, it rises in the southeast. As the sun's position changes, shadows and sunlit images are projected onto the rock carvings. These projections mark the winter and summer solstice, the shortest and longest days of the year, as well as the equinoxes, the midpoints between the two solstices. Evidence also indicates that some petroglyphs interact 45 days before and after the winter solstice.
The above information was adapted from the National Park Service.