Native America Skies: Lunar Standstill in Chaco Canyon

In any given month, the rising moon swings between two extremes on the eastern horizon, similar to the oscillation of the rising sun during the year. When the moon reaches its maximum northern or southern declination, it has a “standstill” similar to the sun at summer and winter solstices. The standstills could be said to be the moon’s equivalence to the Solar Solstices. [for details on lunar standstills, refer to

Native American Skies: Lunar Standstills]

Throughout the world, the cycles of the sun and moon have been diligently observed and recorded by ancient cultures. Today, with computers and wristwatches, we no longer have to depend upon our astronomers for calendrical information. So, we tend to ignore the movements and cycles of the sun and moon. But in ancient times, the seasons, holidays, years, and lunar cycles were marked and observed by astronomers sometimes in elaborate observatories. Tracking a Lunar Standstill was no small task for a people whose life expectancy was much, much shorter than today. One might not be alive to see more than one cycle since Lunar standstills occur in 18.6 year cycles. But, nonetheless, they were noted by ancient cultures in well-known sites around the world including Stonehenge, Callanish, Chimney Rock, Colorado and Fajada Butte at Chaco Canyon, New Mexico.

Atop Fajada Butte is an extraordinary ancient observatory. It was discovered by Anna Sofaer while cataloging petroglyphs in Chaco Canyon. The site has come to be known as the “Sun Dagger” site. [see the exhibit in Albuquerque] This site in Chaco Canyon, New Mexico, is, in many ways the most impressive of all the known Lunar Standstill sites. Even its discovery in 1977 was magical. Ray A. Williams describes it this way:

Finding the calendar device was a mixture of good luck and insight. As part of a team making a major rock art survey of the canyon, artist Anna Sofaer was recording the rock art at the top of the butte. While investigating a large pecked spiral hidden behind three large stone slabs on the southeast side of the butte, she was astonished to see a narrow dagger of light appear on the spiral and begin to move downward across it just to the right of center. In about twenty minutes the spectacular daggerlike appearance was over and the lighting around the spiral had returned to its normal dimness.” [See a video of this phenomenon]

Being there only a few days after the summer solstice, Sofaer understood the significance. She joined forces with others and studied the site and discovered that the “daggers of light’s” movement across the spiral and was an accurate indicator of the solstices and the equinoxes. Further study led her conclude that it also tracked the lunar cycle. Note that the glyph has 19 spirals. As mentioned above, the lunar cycle takes 18.6 years. Not as obvious is a line pecked into the stone bisecting the spiral. Sofaer suggests that this line denotes the lunar shadows during the course of the cycle.

Unfortunately, when word got out about the site, there was a flood of people willing to make the arduous climb up the butte to view it. But, because the soil beneath the stone slabs was fragile, one of the slabs shifted and now it no longer functions as a solar/lunar calendar. However, if you would like to see the phenomenon for yourself, Sofaer and a team have built an interactive, 3D model that can be seen at the New Mexico Museum of History and Science in Albuquerque, New Mexico.

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