A SUN-AND-SPIRAL CLOCK
The astronomical sophistication of ancient humans becomes more obvious each year. A novel method of keeping track of the seasons has been discovered on an isolated butte in New Mexico. Here, the Anasazi, who occupied Chaco Canyon between 400 and 1,300 A.D., carved spiral petroglyphs into the face of a cliff. Then, they arranged stone slabs so that sharp slivers of sunlight fell on the spirals. The precise position of the sliver of light depends of course upon the location of the sun. The solstices and equinoxes are registered by unique configurations of light slivers and spirals. In contrast to other calendar sites, which rely upon the rising and setting points of sun on the horizon, the New Mexico clock depends upon the altitude of the sun at midday. Slivers of moonlight on the spirals also seem to have astronomical significance.
(Sofaer, Anna, et al; "A Unique Solar Marking Construct," Science, 206:283, 1979.)
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