For amateur archaeoastronomer John Rudolph, the Bainbridge petroglyph is like a postcard from the past.

Rudolph believes he can read the meaning of the carved stone that juts from a Bainbridge beach as if it were a message from ancient islanders.

“The purpose of the site is to determine what time of year it is,” Rudolph says. “The petroglyph lies precisely west of the Skykomish canyon 60 miles away. On the vernal and autumnal equinox, one sees the rising sun shining straight through the canyon, if one is standing at the petroglyph.”

Rudolph suggests that such a calendar system would serve important functions for the early islanders, such as marking the return of the salmon.

Co-founder of the Battle Point Astronomical Association and Ritchie Observatory, Rudolph will share his interpretation of the petroglyph – literally, a rock drawing fashioned by prehistoric people – in a lecture Oct. 28.

The worn chunk of sandstone, about four feet high and 12 feet long, is carved with row of wide-eyed faces that inspired the Suquamish name “Haleets,” meaning “many faces.”

Rudolph correlates the carvings to the lunar calendar, noting the similarity of the faces to the moon’s features.

“They had pragmatic reasons for setting the stone,” Rudolph said, “overlaid with ceremonial reasons. Maybe they celebrated the return of the sun, and summer light. The Hopi people do this every day – they stand on a mesa and mark where the sun rises.”

Archaeoastronomers have researched similar sites world wide. Since conventional dating methods wouldn’t work on the Bainbridge petroglyph, a stone scrubbed clean by sea water twice daily, Rudolph estimates that the stone might have dropped from the glacial moraine just 1,640 years ago.

“That still doesn’t tell you when the petroglyph was made,” Rudolph says, “but we know it wasn’t, say, 2,000 B.C.”

Features of the petroglyph remain mysterious. For example, no one can tell whether the stone was found in place or moved to the site.

“Still, it’s important to speculate,” Rudolph says. “You draw up a hypothesis and you test it.”

Despite his scientific approach, the petroglyph has become a permanent feature of Rudolph’s imagination, deeply connecting him to the people who carved and used the stone.

“The stone attaches you to native people who were very smart, very observant and immersed in nature in a way that we are not,” he said. “It opens a window into what these people were concerned about and a little glimpse into their view of the cosmos.”

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Archaeoastronomer John Rudolph presents a lecture on the Bainbridge petroglyph, at 4 p.m. Oct. 28 at Island Center Hall.

Admission is free to historical society members, $5/adults, $2/students. For information, call 842-2773.