Thursday, November 15, 2012

Archaeoastronomy -- Fajada Butte -- Sun Daggers

First of all, what is archaeoastronomy?  It is the study of how the ancients studied or used astronomy.   The position of the stars in the night sky; the movement of the sun across the horizon throughout the year; the movement of the Moon across the horizon on its eighteen-nineteen year cycle; were all studied and recorded and used by the ancients as their celestial calendar.   Knowledge of these cycles helped the ancients to know when to plant their crops, or migrate, celebrate their religious holidays, and many other important events during the year.

In the heart of New Mexico there is an arid canyon called Chaco Canyon that was once the center of the Anasazi culture.  In this canyon stands an ominous butte called Fajada (fa-ha-da) Butte.  Atop this huge 450 ft-high formation are three large sandstone slabs that lean up against the southern wall.  On the wall behind these huge stones, the Anasazi astronomers chiseled two large spirals.   At noon every day the sun shines between the stones and casts shaft(s) of light across the spirals.  Popularly called “daggers of light”, the dagger materialize before noon in the upper left of the spiral and then spread across the spiral to project a “dagger” covering the spiral and then clears off the spiral top to bottom.   It is an amazing, almost magical occurrence.
Click for video of Sun Dagger

The Sun Dagger phenomenon was first noticed by artist Anna Sofaer in 1977 when she was a volunteer recording the petroglyphs on Fajada Butte.  On her first visit, she noted the three stone slabs leaning against the cliff in front of two spiral petroglyphs on the cliff wall.  On her second visit, she happened to be at the site around 11 a.m. and witnessed the dagger of light bisecting one of the spirals.  An amazing stroke of luck since the dagger only appears for about 18 minutes each day.  Realizing that the summer solstice was imminent, she correctly recognized the site as an important archaeoastronomical site.

The following year,  she founded the “Solstice Project” to focus on the study, documentation and preservation of the Sun Dagger site.   Her team learned that for the spring equinox, two daggers appear.  A smaller dagger bisects a smaller spiral through its center, whereas the larger dagger pierces the larger spiral off center.  For the summer solstice, the larger spiral is bisected by a larger dagger through its center.  The autumn equinox is the same as the spring equinox.  Then for the winter solstice, two large daggers embrace the sides of the larger spiral like bookends.  Even more remarkable, it was observed that the 19 segments of the larger spiral marked the 19 year movement of the moon from minimum to maximum across the horizon.


At the Archaeoastronomical Symposium at Queen’s College, September, 1981, Anna Sofaer submitted a paper on her work .  It was the conclusion of the symposium that the Sundagger Site is the only known site in the world where both the solar and lunar extremes are marked.
 

 
For over one thousand years, the stone slabs produced a dagger of light to mark the solar extremes and marked the lunar shadow marching through its 19 year extremes.  Its rediscovery  generated so much interest that the many visitors eager to observe the site first-hand tramped down the soil next to the slabs prompting the site to be restricted and not even the park staff are allowed to visit the Sun Dagger site today.   Unfortunately, the damage was fatal and caused the slabs to shift.  As a result, the slabs no longer produce the daggers of light as they once did.  The restriction was placed too late to save it.
 

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