This June 21, 2004 image taken at Hovenweep National Monument shows a spiral petroglph illuminated shortly after sunrise on the summer solstice. Not unlike possible sun watching stations in Chaco Canyon, this example indicates that ancestral Puebloans may have taken advantage of natural solar markers, carving designs to mark the seasons.
Photo Credit: Troy Cline
Read More about this ancient mystery that was featured in the Technology Through Time section of Sun-Earth Day 2005!
The alignment of Sun, Venus, and Earth comes in pairs that are eight years apart but separated by over a century. For example, the last pair happened in December 1874 and December 1882. The next pair would be in June 2004 and June 2012. After 2012, subsequent pairs will be in December 2117 and December 2125.