The images reveal themselves slowly: a hot air balloon covered in moss, an NYPD helicopter darting across a granite sky, the delicate outline of what appears to be the Space Shuttle. Overhead, satellites dutifully orbit through space. This is no ordinary astronomical display. On a steep granite outcropping that lies within earshot of a major New York roadway, artist Kevin Sudeith has carved a series of delicate petroglyphs that depict a variety of air traffic.

It is an unusual juxtaposition of technique and imagery: crude rock carvings -- of the sort that have been produced for tens of thousands of years -- depict objects that represent the latest and greatest in scientific achievement.

"It's the cutting edge of human technology," said the clear-eyed Sudeith, who still carries a bit of a twang from his native Minnesota. "It could be there and we don't know about it. I'm interested in documenting it in a permanent way."

Since 2008, this itinerant artist has carved petroglyphs into stones around North America, from Cape Breton to California -- documenting facets of local culture and his long-running interest in space. ("When I first got a computer, the first thing I did was went online and looked at the Mars rover photos at NASA," he said. "Space imagery is amazing.")

Many of the pieces are done with the permission of land owners. Others are executed in abandoned, overlooked bits of parkland -- of the grim, dirty sort that can sometimes be found jammed between a couple of roadways.

"One of my goals in doing rock art in remote places is that it hopefully adds something to the place," said Sudeith. "That it makes something out of nothing."

Over the last couple of years, he has bounced in and out of New York City, planting roughly two dozen petroglyphs in the greater metropolitan area -- on boulders and granite outcroppings, amid leaf litter and hypodermic needles.

(For legal and other reasons, he prefers not to disclose their locations. Plus, he likes to give intrepid explorers the thrill of simply happening upon them.)

Sudeith, who was born in St. Paul, but received his MFA in painting from the School of Visual Arts in Manhattan in 1995, says that his work is a way of creating a long-lasting record of our moment in time. In Nova Scotia, he recorded species of fish harvested by local fisherman. In Colorado, he did bear. On a rugged hillside, he carved images of area pick-up trucks. In his New York work, he's included the police department's high-tech helicopters.

"You see these ancient works of rock art that are beautiful and reveal things about cultures that don't exist anymore," he said of his inspiration. "Some of the carvings in the Southwest, they don't know what happened to the people that made them. They disappeared and that's all that's left of them. And that interests me -- to make a very permanent document of our moment."

Ultimately, it's about leaving little surprises for intrepid explorers -- a type of public art that takes place far away from high-traffic galleries and plazas. "People who come across work they are not expecting to see enjoy the surprise of it -- of coming across some unexpected thing," he said. "That is very rewarding for me."

To hear Sudeith talking about his work, click on the audio file below. His Web site Petroglyphist.com contains additional images of his work. (Special thanks to the band Ohioan for the snippet of their song "Being Cold" for our audio.)