Star trails over rock carvings. Time-exposure image of stars passing over petroglyphs engraved in a rockface by ancient Atacameno people. Star trails are formed by the apparent motion of the stars in the sky as the Earth rotates on its axis. Here, in the southern hemisphere, the concentric star trails form around the South Celestial Pole. Photographed at the Hierbas Buenas rock art site, Rainbow Valley, Atacama Desert, Chile.