What, If Anything, is Standing Still?
Let it be noted at the outset that neither the sun nor the .. moon ever physically stands still. There is no evidence that the earth ever stopped spinning on its axis, unless of course you subscribe to a literal interpretation of Joshua 10: 12–13.
Recent newspaper coverage (New York Times September 29, 2006) has sparked interest in an obscure lunar event. This phenomenon, familiar to archeoastronomers and a few new age types, is called a lunar standstill. The standstill manifests itself as a series of spectacular moonrise events at Chimney Rock, an ancestral Puebloan (Anasazi) site in southeastern Colorado. The moon rises between two immense sandstone spires when viewed from the ancient Chacoan Great House located on a narrow razorback ridge 1000 feet above the nearest water source. The Great House was constructed in 1076 AD and the site abandoned by 1125 AD. This area is related to the central site of the ancestral Pueblo in Chaco Canyon, New Mexico and to the later settlement at Mesa Verde in southeastern Colorado.
The current set of moon rise alignments occur only a few times between July and December each year. They started in 2004 and will end in 2007. The moon will not rise between the spires again until 2022. This series will end in 2025. If you noted a difference of 18 years and related that to the Draconic lunar cycle then you may go to the head of the class. This cycle can be projected back in time. It is interesting to note that a series of moonrise alignments started in 1073 AD just before construction of the Chacoan Great House began.
Lunar motion apparent to the naked eye is a complex compounding of three major characteristics:
1. The 23.5 degree tilt of the earth on its axis with respect to the plane formed by the earth’s orbit and the sun (ecliptic).
2. The annual motion of the earth/moon system around the sun.
3. The 27.3 day orbit of the moon around the earth in a plane tilted about 5 degrees with respect to the ecliptic (plane of the earth’s orbit around the sun).
Fig. 1: Lunar orbit. The blue grid is the ecliptic plane with the sun at the center. The earth’s orbit is represented by the blue oval. The lunar path is represented by the dotted red spiral.
The combined effect of the monthly lunar orbit in the tilted plane and the earth’s annual orbit around the sun looks to an observer remote from the earth’s surface like the dotted spiral in Figure 1. The moon spends half the month above the ecliptic plane and half below the plane.
The points where the moon passes through the ecliptic are called the lunar nodes. The line connecting them was called by classical (Greek) astronomers the “dragon” with one node the head and the other the tail. At six month intervals, a new moon or full moon occurs close enough to the node for either a lunar or solar eclipse to occur. This was the dragon swallowing the celestial objects.
Solar gravitational perturbations of the lunar orbit cause the line of nodes to precess with a period of 18.6 years. This perturbation results in three different lunar cycles:
1. The Metonic cycle: Lunar phases occur on the same calendar date at 19 year intervals
2. The Draconic cycle: Lunar declinations vary five degrees on either side of the solar declination resulting in maximum and minimum declinations at 18.6 year intervals;
3. The Saros cycle: The new moon returns to the same node at about the same distance every 18.06 years resulting in a repeat of the calendar dates for eclipse seasons.
The direction of the rising and setting sun or moon was tracked and marked by many ancient cultures around the world. Solar behavior is relatively simple. As the earth orbits the sun, the North Pole tilts toward the sun until passing the fall equinox. It then tilts away, passing the winter solstice (maximum tilt away) until it passes the spring equinox. The pole again starts to tilt toward the sun, passing the summer solstice (maximum tilt toward). The length of the day and the direction of sunrise and sunset depend on the tilt of the earth’s axis. At the equinoxes when the North Pole is not tilted toward or away from the sun, the time from sunrise to sunset is exactly 12 hours (equal hours of light and dark—equi-nox) and the direction (azimuth) of sunrise is due east and sunset, due west. At the summer solstice the sun rises in the northeast and sets in the northwest, reaching a maximum altitude above the horizon which will depend on the observer’s latitude. From these extreme positions, the azimuth changes daily, moving toward due east/west and then reaching a maximum point in the southeast/southwest at the winter solstice.
Fig. 2: The regular annual variation in solar sunrise azimuth over a 20 year period.
The rate of azimuth change is very slow near the solstices and quite rapid near the equinoxes. The point seems to stand still from one sunrise to the next as the solstice is approached and for several days after. (sol-stice is “sun stands still” in Latin). Fig. 2 shows the annual variation in sunrise azimuth over a 20 year period.
Visualization of the variation in lunar azimuth is possible when we recognize how it is tied to the azimuth of the sun. The new moon is aligned with the sun so the new moon azimuth must coincide with the sun. The new moon rises at exactly the same point on the horizon as the sun. The full moon is 180 degrees away from the sun and so the azimuth of full moon rise must be 180 degrees from the azimuth of sun set. Each month the azimuth of moonrise migrates along the eastern horizon from a point coincident with the sun to a point opposite sunset. This approximates the annual solar azimuth migration on a monthly cycle. Some writers term the monthly extremes, “lunistices” or standstills because the daily rate of change in azimuth is relatively slower there. Figure 3 shows the monthly variation in moonrise azimuth over a 20 year period.
Figure 3 reveals the complexity added by the five degree tilt of the lunar orbital plane. This effectively adds or subtracts up to five degrees from the declination of the moon. The extreme declinations which lead to extreme azimuths are called the major and minor standstills. The moon periodically rises between the sandstone spires at Chimney Rock when the azimuth is near the northernmost part of a major standstill.
Fig. 3: The monthly variation in moonrise azimuth over a 20 year period.
Archeoastronomy—More than alignment hunting?
Highly publicized work in the 1970’s by Archibald Thom, a retired English engineer, attempted to prove that Stonehenge was an ancient observatory. He theorized that Neolithic (3000 BC) observers made highly accurate measurements of solar and lunar events, marked them out with stones and posts and used them to predict eclipses and precisely measure the length of the solar year. He extended his researches to many other Neolithic stone circles and lines throughout the British Isles, eventually concluding that ancient builders had developed a standard measuring system based on a so-called “Megalithic yard.” His work greatly excited many amateurs and led to a frenzy of alignment seekers at various archeological sites. Most of his work did not stand up to rigorous statistical analysis and so is no longer taken seriously by the professional community.
His work still fuels the “mysterious ancient knowledge” enthusiasts and those who believe the ancients gained this knowledge during visits from extra terrestrials. John Rudolph, a very enthusiastic archeoastronomer and one of BPAA’s founders, induced me to chase alignments at an ancient Native American site in the high desert near Susanville, CA (See “Dusty and Lefty Meet the Petroglyph Groupies”, BPAA Dec. 2003 Newsletter). The results of our efforts were written up in the BPAA Newsletter back in 1997. Our most interesting finding was a unique and complex petroglyph deeply pecked into the rock of an almost inaccessible cave crevice. John and I carefully measured the distance and angular relationship between points on the glyph and the tip of a crevice between two rocks which formed an opening to the sky just above the glyph. This enabled me to model the glyph on a computer and see if a dagger of moonlight might reach the glyph. The computer predicted that a dagger of moonlight would sweep across the glyph at full moons near the winter solstice for a few years around a major lunar standstill. John trekked to the site one December but unfortunately it was not near enough to the lunar standstill to verify my predictions. Now (December 2006) would be the time to verify the computer predictions but my enthusiasm has dimmed—particularly when one visualizes huddling in a cave through a high desert winter night. I wasted some time trying to convince myself that the glyph might provide eclipse indications. Unfortunately, any attempt to interpret this very rich petroglyph site is seriously hindered by the complete lack of information on the culture or people who created it. The site might be as early as 2000 BC, much older than the Chaco civilization.
Archeoastronomy becomes relevant only when it can be related to a larger body of cultural knowledge. Multiple sites showing similar alignments or commemorations provide strong indications of cultural links to the sky. The multiple site link makes Chimney Rock very significant. The earlier ceremonial center of the Anasazi in Chaco Canyon (950 to 1100 AD) contains a dramatic spiral glyph at Fajade Butte. A summer solstice sun dagger formed by a crevice between two large rocks passes through the center of the glyph. Lines scribed through the center and tangent to one side of the 19 turn spiral mark the lunar shadow near the minor and major standstills. After abandoning both Chaco Canyon and Chimney Rock, the ancestral Puebloans settled at Mesa Verde in Southeastern Colorado. J. McKim Malville, noted archeoastronomer from the University of Colorado, discovered the Chimney Rock alignment in 1988 and shortly after that found a similar alignment at Mesa Verde. It appears that the Mesa Verde astronomers tried to duplicate the natural observatory formed by Chimney Rock and its companion sandstone spire with two manmade towers. Major standstill moonrises align between the towers and windows in the Sun Temple.
You can still observe a lunar standstill event at Chimney Rock next year. This year’s events are sold out. Tickets for 2007 events will go on sale May 15, 2007. I took a moonlight tour of Chaco Canyon several years ago. We had no spectacular alignments but the location is breathtaking. I am inspired to visit Chimney Rock next year. It will be summer and I will remember John Rudolph with great fondness.
http://www.chimneyrockco.org/MalvilleMLS.doc “Rediscovery of Lunar Standstills at Chimney Rock” by J. McKim Malville
http://www.chimneyrockco.org/Web site for the Chimney Rock Archeological Area.