In 1986, Halley's Comet passed through our neighborhood much as it has every three-quarters of a century for at least the last two millennia. Unfortunately, the Earth was not in a very favorable position to give us a good view when the comet was at its best. The image below, photographed from a dark-sky site in southern Arizona, is the best I was able to capture.

Halley's Comet in the early morning sky of March 21, 1986 along with
the constellation Sagittarius and a serendipitous meteor appearing
to streak from the bright, central bulge of the Milky Way.

After Halley's Comet moved on towards the cold depths of the Solar System, I didn't find much reason to think about it, especially due to the excitement generated by the two great comets of the 1990's—Hyakutake and Hale-Bopp.

Recently however, at a Hohokam petroglyph site in southern Arizona, I found a panel of glyphs with one that looked like a comet (left). It consists of a circular comet head with a tail streaming down. Inside the head is a "+" symbol which the Hohokam often used to denote a star. That fit perfectly since most comets have a bright, star-like central condensation within the more nebulous head.

What bothered me was the downward pointing tail. Comet tails usually have an upward trend. This one aspect was the only thing keeping me from feeling comfortable calling this a comet glyph. So I decided to look at some great comet events of the past to see if I could find one that fit.

I quickly found it easiest to concentrate on Halley's Comet since its orbit has been well defined and checked against historic astronomical sightings. Also, this flashy periodic comet has put on some pretty fantastic shows over the centuries. I began with the Halley events of 1222, 1145, 1066, 989, 912, 837 and 760 since they definitely fit the time frame of the Hohokam.

It was a simple matter to obtain the information needed for this exploration. I already used the commercial astronomy program SkyMap, and to depict comet tails, I added a freeware program called Cartes du Ciel. I found a good set of orbital elements in a research paper by Donald K. Yoemans and Tao Kiang. With these magical numbers entered into the software, I could reliably tell where the comet appeared in the sky, how fast it moved, and even the direction and relative length of its tail.

Only one of the Halley's Comet apparitions I checked displayed a downward pointing tail—the fantastic event of 837 CE (shown in part at left). The unusual tail orientation was made possible in part by the comet's close brush with Earth. In fact, about an hour before midnight on April 9, 837 CE, Halley made its closest known approach to our planet—about 2.66 million miles.

All this was very exciting to find out, and it went a long way in helping me feel confident saying the petroglyph in question depicts a comet. It would be even more exciting to be able to call it a glyph of Halley 837, but there is definitely not enough evidence for that.

In the end, my explorations into tail direction could be meaningless. The Hohokam glyph maker, most likely a shaman, was probably little concerned with accurately recording the comet. The petroglyph panel was more likely religious or ceremonial in nature. The comet glyph could depict a particular aspect with which the people were concerned. To me, the symbolic comet looks as if it's flying away. Who knows, maybe the glyphs were a shaman's ceremonial attempt to drive away the bright, fast moving and powerful unknown spirit from the sky. Or possibly it was an attempt to ally with and share in the power. These are questions for anthropologists, not me.

After spending so much time scrutinizing the 837 CE passage of Halley, I felt I had almost witnessed the event first hand. In my mind, I stood on that hill where the comet glyph now resides, and watched the giant tail of the great comet elongate and merge with the Milky Way. Now, I don't peck on rocks, so I am not about to make a petroglyph panel to symbolize my experience of the event. I am a photographer however, and I could hardly keep from making the image below. Now I have my own spiritual memory of the closest known approach of the most famous comet in history.

This represents how Halley's Comet may have looked on April 9, 837 CE
at 4:30 AM. I used four different images to make the composite: the
Milky Way, comet Hale-Bopp, a landscape looking south from the
hill containing the petroglyphs, and a close-up of the glyphs.

Note: I included the circle cluster petroglyph because at one point I thought it might relate to the Milky Way. It is already well accepted that swaths of dots or small circles were used in large petroglyph panels to represent this nebulous pathway traveled by spirits. I figured maybe the small cluster could depict a smaller, noteworthy section of the Milky Way, say the bright Sagittarius Star Cloud in the center of the image above. Visually, that makes some sense, but it is mostly based on proximity, not on meaning. Artistically, the circle cluster helps balance the image.

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