three stones, two spirals, one sun and one moon
Joseph Campbell’s observations in the Historic Atlas of World Mythology Series.
quoted from above:
“on the rock face behind the vertical slabs are engraved two spirals, a larger of nine and a half turns and a smaller, to the left, of two and a quarter. Toward noon on the day of the summer solstice, a dagger of living light passes through the center of the larger spiral while, in a related effect, a small spot of light, hardly noticeable, shines for but two minutes somewhat to the left of the lesser spiral.”
“Through the following months of July, August, and September, these two beams move steadily, day by day, to the right, until on the day of the fall equinox, September 21, the leftward beam, now much longer then the first, cuts through the center of the lesser spiral. Thereafter, the rightward movement continues, and this second beam ever lengthens. By noon on December 21, the day of the winter solstice, the two darts, now of equal length, perfectly frame the larger spiral, after which the movement, day by day, is from right to left. At noon on march 21, the day of the spring equinox, the positions of the light beams are exactly as they had been September 21, and by the summer solstice the cycle is completed.
The sunlight travels across the spiral from above to below, following the point of light. In the crude illustrations below, a rough representation of the function of the calendar
“… the patterns formed by moonlight shining between the slabs are as clear as hose of the day, and when the moon’s declination is anywhere between the solar extremes of 23.5 degrees and minus 23.5 degrees, the patterns formed are the same as those of the sun. However, in the course of a cycle of nineteen years [the Metonic Cycle], the Moon’s declination for a part of that time, goes beyond these solar limits. This periodic extreme was not reached again until 1987, when photographs taken on November 8th (the night the moon attained the most northerly extreme of its nineteen-year excursion) confirmed predictions… that the rising moon, shining on the vertical slabs, casts a shadow which is tangent to the left edge of the spiral. It has been noticed that the count of the lines of nine and a half turns crossing any diameter is 9 + 10 = 19, and we know that once every nineteen years there’s a full moon on winter solstice eve.”
“The Anasazi Calendar utilizes three large rock slabs to baffle and focus both the sunlight and the moonlight, so that significant celestial intervals are marked by a sliver of illumination that falls upon and traverses one or another of the spiral petroglyphs on the adjacent cliff face.”