The search for extraterrestrial intelligence, or SETI, turns 50 years old this year. By scanning the cosmic radio dial, it has forged a scientific beachhead into the mystery of whether we are alone in the universe. One of its main disciples has written a book chronicling the history and offering an apologia as to why it is a worthy cause.

As senior astronomer at the SETI Institute, Seth Shostak spends a good deal of his time publicly championing the search for extraterrestrial intelligence. He writes popular articles, gives presentations and even offers technical advice on movie sets (showing Keanu Reeves, for example, how to write the Greek letter "mu" on a blackboard).

In his new book Confessions of an Alien Hunter: A Scientist's Search for Extraterrestrial Intelligence, Shostak provides an insider's account of the SETI universe.

Shostak defends his choice of work from detractors that would say he and his companions are tilting at windmills. He is neither bitter nor strident - instead he weighs the opposing viewpoints very carefully (sometimes obscuring his own convictions).

But the book is in no way stiff. Shostak pokes fun of Hollywood depictions of aliens and lampoons several hoaxes like the Face on Mars.

He peppers his prose with clever turns of phrase and a seemingly endless supply of analogies, such as "the moon was drier than a Mark Twain quip," and "finding clues to life's earliest moments on Earth is tougher than overcooked roadkill."

This is an enjoyable read both for those who believe "the truth is out there" and those who think that we pretty much have the galaxy to ourselves.

A-Hunting We Will Go
Although some early attempts to make alien contact date back to the 19th century, SETI in its current form began in 1959, when Giuseppe Cocconi and Philip Morrison published a paper claiming that interstellar messages would best be sent by radio.

Independently, Frank Drake devised a search of nearby stars, called Project Ozma, with an antenna at the National Radio Astronomy Observatory (NRAO) in West Virginia.

In the years that followed, radio astronomers used spare telescope time to occasionally dabble in informal SETI surveys. One of these dabblers was Shostak. In the 1970s, while doing postdoctoral research at the NRAO, he filled the time between scheduled galaxy observations with impromptu peeks at nearby star systems. As he writes in his book:

"This was like feeding pocket change to a slot machine on the off chance of hitting the jackpot - in this case, an artificial signal that would come booming in and make my day."

Around this same time, some of the SETI hobbyists began to organize themselves. With NASA funding, a formal search strategy was put together and the necessary computer equipment was developed for analyzing incoming radio waves. In 1984, the non-profit SETI Institute formed as the organizational nucleus of various SETI-related research projects (Shostak joined in 1991).

NASA funding was pulled in 1993, but private funding allowed the research to continue. Under the name Project Phoenix, SETI astronomers examined about 750 star systems from 1995 to 2004.

Without a dedicated SETI telescope, the alien hunters contented themselves with hopscotching between existing radio observatories: mainly the NRAO's Green Bank telescope, the Arecibo telescope in Puerto Rico, and the Parkes telescope in Australia.

They used their allotted time at these facilities to point the antennas at different stars in the sky, eventually scanning millions of channels between 1,200 and 3,000 MHz on the radio dial.

In describing how this data was analyzed, Shostak jokes about Hollywood's portrayal of SETI work:

"You can now appreciate one of the more delicious incongruities of the movie Contact. In the film, Jodie Foster sits on the hood of her car in the New Mexico desert, with earphones playing celestial static to her bored brain. But in the technically correct version, she would be wearing tens of millions of earphones (or using a computer). Surprisingly, when this fact was pointed out, Warner Brothers refused to give it much consideration. Presumably the production company worried that wearing millions of earphones would crowd the shot."

A Lonely Quest
Another incongruity in the movie is that Jodie Foster makes contact with other beings. No such luck yet for SETI's real-life protagonists.

It is perhaps telling that the most dramatic event to occur in decades of actual alien hunting was a false alarm. Shostak describes the events of June 24, 1997, when the SETI crew had been up all night following a signal that had the makings of an interstellar "hello.":

"The possibility of discovery was making me fidgety. My immediate worry, ironically, was about trivial matters. If the signal turned out to be real - if it really was beamed from aliens - then my schedule for the week was going to be completely messed up.... We were on the verge of proving that humankind had company, that other intelligence dwelled among the stars. But I wondered if we were ready to hear from beings that would make Homo sapiens look like an also-ran."

Although the radio blips later turned out to be from a solar-observing satellite, Shostak believes a bona fide message could be picked up in the next few decades. This optimism is due to the recently-constructed Allen Telescope Array, a facility dedicated to hunting for alien signals. The ATA will eventually comprise 350 radio antennas scattered over a half mile stretch in northern California. Shostak writes:

"A straightforward calculation shows that by the year 2030, the Allen Telescope Array could check for signals in the direction of a million or more star systems."

If the number of cosmic neighbors estimated by SETI pioneers Frank Drake and Carl Sagan are right, then one or more of these stars is home to an alien civilization that is sending us a message - a message that is surely going to mess up all of our schedules for the week.

A Life's Gamble
Shostak clearly explains what astrobiologists assume when they estimate how many radio-broadcasting societies fill our galaxy. He also gives his take on what these aliens might be like (he's guessing they are computers) and whether they are already here poking around in our air space, farmlands and bedrooms (he's pretty sure they aren't).

But there's one issue that Shostak comes back to several times throughout the book. Why do SETI at all?

"Many scientifically literate critics point to the Fermi paradox, or some variant thereof, and pronounce that the verdict is already in: Our galaxy is, at best, only sparsely inhabited. Even those who accept SETI's mission frequently opine that it may take generations to succeed, if success occurs at all. So... why would I spend my one-and-only brief moment on the stage of life chasing this particular rainbow? ... [It] is the fact that SETI addresses a truly big-picture question. This is exploration on the scale of those European sailors who plied and plotted the world at the start of the 16th century. Unless our concept of the cosmos is gravely in error, SETI is the beginning of the last major foray into the unknown."

To those who would say that SETI is going about it all wrong, that future technology or scientific discoveries will revolutionize alien searches, Shostak answers with another analogy to ocean exploration:

"Imagine being a member of the Spanish court in the late 15th century, counseling Columbus. You might suggest he give wooden ships a pass and hang fire for 500 years, after which he could cross the Atlantic in hours eating low-grade meals off his lap. Yet Columbus discovered an extraordinary new world, and his wooden ships were (just) good enough to find it."

Will the Allen Telescope be SETI's Santa Maria? We'll have to wait and see.