On Aug. 16, 1977, a volunteer looked over a stack of data from Ohio State's Big Ear radio telescope and saw something surprising. He grabbed a red pen and wrote down one word in the margin -- Wow!.

On Aug. 16, 1977, a volunteer looked over a stack of data from Ohio State's Big Ear radio telescope and saw something surprising. He grabbed a red pen and wrote down one word in the margin -- Wow!

DELAWARE, Ohio - If you call Jerry Ehman at home, you'll likely reach his answering machine. He wants to hear who's calling before he picks up. He's not anti-social, just cautious. It could be another alien fanatic. Or another reporter.

Both want to talk with him about the signal. The "wow" signal.

Though it's been nearly 33 years since he discovered a mysterious space signal, there is still a lot of interest.

After all, his find is the closest thing to alien contact that man has ever recorded.

Ehman was even mentioned by name in a 1994 episode of The X-Files called "Little Green Men."

"That was cute," he said.

Every time his name shows up in a newspaper story, on a blog or a TV series about aliens, new questions pop up about what happened on Aug. 16, 1977. Star Wars was still in theaters and Elvis had left the building that morning when Ehman began to decipher another stack of printouts from Ohio State University's Big Ear radio observatory in Delaware.

Decades later, Ehman, now 70, rattles off the sequence that made him famous: "6EQUJ5."

"Numbers we'll always remember," said Bob Dixon, 71, who was the assistant director of the Big Ear radio observatory during its heyday in the early 1970s.

Grant money from the National Science Foundation was rolling in, and SETI (the search for extraterrestrial intelligence) research was hot. The Big Ear, which had scanned the heavens for natural radio waves, was beginning to seek artificial signals. Alien signals.

And in 1977, just months before Close Encounters of the Third Kind opened in theaters, Ehman "heard" something that made him and the Big Ear famous. That something might have been the only alien "hello" we've ever heard.

When he was growing up, Ehman never put much thought into UFOs or extra-terrestrials.

"As far as I know, I've never been abducted," he said. "I'd never seen any aliens, so that didn't interest me."

His future, Ehman thought, was in agriculture.

And for a while, before he earned a doctoral degree in physics and worked in radio astronomy, Ehman considered becoming a farmer.

He spent his first 21 years in the hills of western New York. When he was 8, his family moved to a dairy farm.

Ehman went into high school ready to learn about raising crops. He even grew strawberries in a school agriculture program, but soon lost interest. It wasn't the same without his dad, who died when Ehman was 11.

So he focused on his other interest: science.

He studied at the University of Buffalo and then the University of Michigan before he went to Ohio State in 1967 to split his time between teaching electrical engineering and working at the Big Ear.

When he didn't get tenure at OSU in the early 1970s, he took a job at Franklin University teaching business classes. But he continued to work at the radio observatory without pay. He enjoyed the work.

Then one morning, he wrote down the word "wow" on a printout and everything changed.

"Oh, I want it to be a signal from an extra-terrestrial civilization," Ehman acknowledges.

Others do, too.

And some go to great lengths to find meaning in the six letters and numbers that Ehman circled in red pen.

Dixon said a man in Poland once called to tell him he had solved the puzzle.

"He said he spent 10 years studying this," Dixon said. "I tried to explain to him that there is no code, there's nothing to decode, that it makes no sense to talk about that."

Just another one for the "crazies file," as he likes to call it.

"I keep getting a call from a guy in the Netherlands," Ehman said. "Says he's got this theory - I could tell he was a flake.

"Now, when he calls, I've got my answering machine, of course."

The Big Ear was built in the late 1950s by electrical engineer John Kraus and operational by 1963.

The antenna, large as three football fields, spent seven years searching for newly discovered deep-space radio sources known as quasars. By 1972, Big Ear had recorded more than 20,000.

From 1973 to 1997, the focus shifted to narrowband radio signals, which are not natural. In other words, the telescope became a SETI scout.

Everything emits an electromagnetic signal or signature. This is why astronomers measure radiation from planets or other objects to learn about their chemical composition. An observer on a far-off planet might be able to measure the radiation Earth emits and learn that it contains hydrogen, oxygen, carbon and other elements and chemicals.

Each of these chemical signals occupies a distinct portion of the spectrum, a distinct frequency. Because hydrogen is the most abundant element in the universe the OSU team chose the hydrogen frequency as its target.

The hope was that extraterrestials might think the same way as SETI researchers and choose that common hydrogen frequency to send us a radio broadcast.

For years, Ehman and others took their printouts and looked for anything that resembled a beacon signal.

The "wow" signal remains the solitary find.

In 1997, the program was shut down. The telescope was scrapped the next year.

Ehman continued to volunteer in Ohio State's radio astronomy program over the years, but stopped in 2008. He volunteers at his church and is considering getting an amateur radio operator license.

Although the Big Ear is no longer around, the search for alien signals has never really gone away. The University of California at Berkeley has a program called SETI@Home , which uses millions of home computers around the world to process data from radio observatories.

What took Ehman and others hours to do by hand is tackled by a computer in milliseconds.

The "wow signal," however, is not forgotten. In fact, it serves as a case study, a lesson in what works and what doesn't.

"It emphasized the importance of doing signal processing in real or near-real time in an interference-rich environment," said Jill Tarter, director of the Center for SETI Research.

If the computers sense a signal, researchers will immediately focus on it to see what it is.

That wasn't the case with Big Ear.

The radio telescope ran for three or four days at a time. Then it was shut down and the data was printed out. Once the 1-megabyte hard drive was cleared, the telescope was turned back on.

So by the time Ehman wrote "wow," the signal was long gone.

So far, the decade-old SE TI@Home program has logged 1 petabyte (1 million megabytes) of data. And it's possible, said Dan Werthimer, who directs the program, that there's a signal in there that contains decodable information - maybe a picture or a language lesson.

"It's looking more and more like the universe is teeming with life," he said.

Ehman agrees, but said he discovered long ago that some scientific fields are more about seeking than finding.

Ever since he wrote down "wow," Ehman and others have worked to rule out other causes: military experiments, distorted space waves, satellites, supernovae, black holes.

So far, the only explanation that seems plausible is intelligent life. Something. Way out there.

"But I can't prove that it was, and I can't prove that it wasn't," he said. "It's an open question."

So he hasn't lost any sleep waiting for the aliens to call.