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!
Earth's magnetic poles reverse their geographic locations every 300,000 years. The last event happened 780,000 years ago.