Near the bottom of the Mormon Trail at South Mountain Park in Phoenix, Arizona, there is a small group of unassuming petroglyphs. Most prominent of this prehistoric Hohokam rock art is a pair of lizard figures with one holding the arm of another having a concentric circle body. City of Phoenix Archeologist Todd Bostwick calls it the Lizard Site in his book Landscape of the Spirits, and includes it in a list of those with possible solar interactions on the summer solstice.

So, on the solstice of 2005, I found myself standing with the lizards waiting for the sun to rise. On a previous outing, I had checked the compass heading of solstice sunrise, and found it pointed straight at Four Peaks. This notched landmark of the Mazatzal Mountains lies 45 miles east-northeast from the Lizard Site. How fitting it would be if the solstice sun rose right in the middle "V" of these sacred peaks.

The lizards and I continued to watch the sky brighten. All of a sudden the first flash of sunlight burst over the horizon. Bull's-eye! A brilliant summer beacon was shining directly from the deepest central notch. It is well accepted that past cultures marked the solstices and equinoxes for ceremonial purposes, and many such "calendar" sites were left by the Hohokam. It seems difficult to believe they wouldn't have used this perfect spot for exactly that purpose.

Of course, few things are ever that simple. Sunrise and sunset points shift slightly over time due to a 2.5 degree change in the tilt of Earth's axis which occurs over a 41,000-year period. We live in a time of the cycle when the axial tilt, called the obliquity of the equinox, is decreasing. This has the effect of drawing solstice sunrises and sunsets in towards those of the equinox. I used astronomy software to calculate the summer solstice sunrise point of 1,000 years ago and found it occurred about 10 arcminutes (1/3 sun width) north of where it does today at the Lizard Site.

I needed something to help visualize how these shifts affected the solstice sunrises over the time period this site might have been used by Hohokam sun-watchers. Using digital images taken at the Lizard Site on the 2006 summer solstice, I constructed the Sunrise Simulator. This handy tool exists as an image file with the sun, ruler and sunrise line on separate moveable layers set against the background of Four Peaks. I made it so the whole sun shows for easy positional reference, but is brighter where it appears above the horizon.

To use it, I find the difference between sunrise coordinates of the year I'm checking and those of 2006. I then reset the rise line by the correct amount and realign the sun. If needed, I can move the sun up or down slightly as long as I keep it aligned to the new rise path. The simulator can also be used in reverse fashion by finding an interesting configuration first, then determining the amount of shift and corresponding range of years.

Before delving into the search there was one more point to consider. It seems that although a visually meaningful solstice interaction would have been useful to the Hohokam for ceremonial purposes, a sun-watcher most likely would need to find an interaction occurring several days before the solstice. Village elders and priests would use this to determine the correct timing of upcoming ceremonies so that preparations could begin.

The number 4 (and multiples: 8, 12, 16 etc.) seems to have had spiritual significance to many prehistoric people. There is evidence that these sacred cycles were applied to many situations including solar interactions.

This is the case at another South Mountain location called the Sun-Struck Site. The top section of the rock art panel is shown at left on the summer solstice with a distinct shadow notch centered on a 5-pointed star symbol. The site has been extensively examined by Wes Holden, retired director/editor of Arizona Highways Book Division and long-time studier of rock art and past cultures. He found convincing interactions of light and shadow with petroglyphs that mark solstices, equinoxes and most cross-quarter days. Some of these preceded the actual event by 4, 8 and 12 days.

With this in mind, I went to the Sunrise Simulator to examine past solar positions over Four Peaks. I uncovered a great set of circumstances that could have been used for most of the 10th through 12th centuries CE. Shown below are views from 9 and 8 days before solstice for the year 1009 CE. You can see that 1000 years ago the sun would rise in the right notch at 9 days before solstice, then move north just enough to rise in the central notch a day later. For nearly 300 years, generations of Hohokam sun-watchers had a location from which they could see an unmistakable sunrise signal to confidently know when it was 8 days before solstice.

The solstice itself had a distinctive interaction as shown below. Sunrise would begin with 2 closely spaced points of light that would merge seconds later. To confirm the eye's ability to see these separate points and also to photograph the sunrise, I calculated where I would need to stand to compensate for how much the sun shifted in 1000 years. I easily saw it and the image I captured is used in the title graphic at the top of the page.

The symbolic joining depicted by this particular sunrise would certainly not have escaped the Hohokam. It may even be echoed by the pair of lizard petroglyphs with which they marked the location. The twosome seems to be male and female, with the latter having a concentric circle abdomen. A circle inside another circle was sometimes used to depict the sun and moon which have a connotation of being opposites: day/night, male/female. Concentric circles can also depict a portal to other levels of being or to the realm of the gods. A portal as part of a woman's body could represent the womb through which new life comes from the joining of opposites.

If Hohokam sun-watchers used the solar interaction at 8 days before summer solstice (SS -8), they would have noticed that the sun rose in a slightly different position over a 4 year period. This happens because the year is actually about 1/4 day longer than the 365 days used in the calendar. The views below represent SS -8 from the years 1008-1011 CE. They have been calibrated to when the sun would first peek out of the right notch to keep the solar altitudes relatively equal to more clearly show the amount of shift.

To visualize what is happening, remember the sun is still shifting north (left) towards the solstice from day to day. Each year, the sun doesn't quite make it as far as it had the previous year. The cycle progresses smoothly until 1011 CE when the SS -8 sunrise sighting has to be pushed to the following day because it occurs closer to that sunrise. This waiting to sight on the rising sun gives it more time to travel northward, creating the jump seen in the bottom illustration.

Notice the sunrise for 1010 CE. During the time the Lizard Site SS -8 interaction was working at its best, every 4 years would present the sun-watcher with an awesome multi-pointed sunrise. On a previous solstice outing, before knowing it might be of special interest, I just happened to take a photo of this sunrise (below). It is a scan of a 35mm transparency which shows a bit too much flaring. I need to shoot it again on digital to get an image that shows the separate points of light better.

The Lizard Site at South Mountain Park marks a location from which useful and accurate summer solstice interactions could have been seen. The site also contains petroglyph figures that seem well suited to the special nature of its particular solstice sunrise. To me, the evidence that this site was used by the Hohokam as a summer solstice "calendar" is quite convincing.

All images are copyrighted by Frank Zullo. Please do not use without written permission.