At the beginning of the wildly popular film The Da Vinci Code, the lead character played by Tom Hanks delivers a presentation titled "The Interpretation of Symbols" and begins by saying "Symbols are a language that can help us understand our past." Two astronomers attending the 208th Meeting of the American Astronomical Society in Calgary, Canada could not agree more.

Image: A petroglyph possibly depicting the supernova of A.D. 1006 (star symbol, right of center) and the constellation Scorpius (scorpion symbol, left of center). The boulder on which the petroglyphs appear is located in White Tanks Regional Park, Phoenix. Credit: John Barentine, Apache Point Observatory. Download larger image version here http://galileo.apo.nmsu.edu/~jcb/sn1006/SN1006_glyph_800_by_600.jpg

They announced this week what is believed to be a link between a historical stellar event and the meaning behind an ancient symbol. John Barentine, an astronomer with Apache Point Observatory in New Mexico and Gilbert A. Esquerdo, Research Assistant with Planetary Science Institute, Tucson, believe an early rock carving, or petroglyph, found in the White Tanks Regional Park in Arizona depicts the well-known supernova of A.D. 1006. The petroglyph is located in an area once occupied by prehistoric Native Americans called the Hohokam. From about A.D. 500-1100, the Hohokam are believed to have lived in this area, outside of what is now Phoenix, Arizona.

Until now, the one-thousand year old supernova was thought to only have been recorded by star watchers in the Old World. Simultaneous written records from Asia, the Middle East and Europe recognize the appearance of a "new star" in the modern constellation of Lupus on May 1, 1006. Confirmation of this proposition would advance understanding of prehistoric Native American astronomy and traditions concerning the night sky. On believing he may have found the first New World record of the exploding star, Barentine says, "The supernova of 1006 was perhaps the brightest such event visible from Earth for thousands of years, reaching the brightness of a quarter moon at peak, yet to date no representations of the event have been identified in Native American art. If confirmed, this discovery supports the idea that ancient Native Americans were aware of changes in the night sky and moved to commemorate them in their cultural record. It may also be of benefit to archaeologists trying to fix precise dates to petroglyphs in the Southwest and elsewhere in the world, providing a rare opportunity to relate a specific historical event to its depiction in rock art."

Traditionally, assigning dates of origination to prehistoric Native American art has been extremely difficult because of the lack of a written language and little continuity with the culture and folklore of historic Native American tribes. Barentine, who studies Southwest archeology as a hobby says, "Quantitative methods such as carbon-14 dating are alternative means to assign ages to works of prehistoric art, but they lack precision of more than a few decades, so any depiction in art that can be fixed to a specific year is extremely valuable." Though he admits, "Without my background in astronomy, I probably wouldn't have recognized the petroglyph for what it might represent."

Image: Simulated night sky looking south from the location of the petroglyph at midnight on May 1, 1006. The horizon profile is a true representation of the site horizon, made from photographs taken at the site and placed correctly with respect to the stars and the direction of true south. The supernova appears just above the horizon near center; the constellation Scorpius grzes the horizon left of center. Credit: Gilbert A. Esquerdo (Planetary Science Institute, Tucson, and Smithsonian Astrophysical Observatory) Download larger image version here http://galileo.apo.nmsu.edu/~jcb/sn1006/sky_and_horizon_1024_by_619.jpg

Barentine and Esquerdo created an accurate model of the night sky on May 1, 1006, to show that the relative position of the supernova with respect to the constellation Scorpius matches the relative placement of scorpion and star symbols on the rock. Petroglyphs such as these are among the most durable and longest lasting human art forms. They are made by pecking, or hammering away, at the rock surface using a smaller, handheld rock. It is the enduring image on this rock that inspired Esquerdo as he says, "Standing in the desert heat after studying the petroglyphs, the span of the ages hit home. One thousand years ago, someone else was standing in that exact spot looking upon the depiction they created of the star they had seen in previous nights. It was the change in the sky that had brought that artist as well as us to that spot one thousand years apart."

Similar petroglyphs have been identified as likely depictions of historic astronomical events in the prehistoric Southwest. One of the most widely recognized examples is the pictograph near Penasco Blanco in Chaco Canyon National Monument, New Mexico. There, a painted rock symbol is theorized to depict the supernova of July 4, 1054. As for the White Tanks Regional Park petroglyph in Arizona and its suspected relationship to the 1006 astronomical event, the results are not fully conclusive. The proposition is advanced and supported through circumstantial evidence. However, chemical dating, which relies on the abundance of certain elements in the rock varnish, could help confine the range of dates in which the petroglyph was created. A result substantiating an early 11th century date of origin would lead considerable credence to the claim that the prehistoric symbol represents the 1006 supernova event. Indeed, "Symbols are a language that can help us understand our past."