The likelihood that one of these space rocks poses a real threat to human lives may be low—researchers at Prince-ton University have placed 1-in-5,000 odds on an asteroid two-thirds of a mile across smacking into Earth sometime in the next century (for comparison, the risk that you will be struck by lightning in your lifetime is about 1 in 3,000)—but the stakes are high. A relatively small 150-foot asteroid that struck Tunguska, Siberia, in 1908 packed the punch of 15 million tons of TNT, equivalent to the largest nuclear bomb ever detonated by the United States. Fortunately, it fell far from human habitation. If an asteroid of the size studied by the Princeton researchers struck Europe or the eastern seaboard of the United States, the death toll could run into the millions. “There’s no upper limit on the amount of damage that could occur if a large asteroid were to hit,” says Roy Tucker, an imaging specialist and amateur astronomer in Tucson, Arizona. “Even the boulders that crumble off the surface of big asteroids could cause Tunguska-like events.”

The American government has responded to the threat with funding to allow NASA to seek out potentially threatening asteroids—just barely. NASA supports the Spaceguard survey to the tune of $4.1 million per year, but that sum of money is not enough to cover the cost of continually monitoring all areas of the sky for near-Earth objects. As a result, Representative Dana Rohrabacher of Southern California has introduced congressional bills that would provide monetary awards to amateur astronomers for their contributions to the asteroid hunt. “The near-Earth object threat to our planet is a vital area of concern,” he says. “We can’t just rely on the government to narrow the information gap, so we’re mobilizing our citizens to identify things that might be dangerous.”

From NASA’s point of view, the value of amateurs is obvious: The more pairs of telescope-aided eyes scanning the cosmos, the greater the likelihood that significant discoveries will be made—and given the budget crunches of the past few years, the agency needs all the unpaid sky watchers it can get. More observers in far-flung locations also mean more vantage points, making it easier to calculate the orbit of a stadium-sized asteroid once it is discovered. At the same time, the number of serious amateurs is growing quickly because of new digital CCD light detectors that can make even modest telescopes powerful enough to observe dim asteroids. “A research-quality microscope can cost $100,000, but nowadays a good telescope might be as little as $10,000,” says Steve Chesley, an expert on near-Earth objects at NASA’s Jet Propulsion Laboratory who analyzes the observations of dozens of amateur astronomers.

Over the past decade, scientists like Chesley have routinely turned to hobbyists for help with important but unglamorous tasks like taking several images of an asteroid to plot its trajectory. In return, they give their amateur acquaintances the same respect as colleagues with advanced degrees—for the most part. “There are only a few prima donnas,” Tucker says. Amateurs and professionals are frequently on a first-name basis. “Dear Ron,” reads an e-mail from Chesley in Dyvig’s inbox, “really appreciate all the assistance! Thanks again, Steve.”

As a result, amateur astronomers are playing a crucial role in the search. Two years ago, Tucker helped discover 2004 MN4 (more catchily known as Apophis), an 800-foot-wide asteroid that looked like it might be on course to collide with Earth in 2029.

In principle, asteroid hunting is accessible to anyone with a decent grounding in astronomy and a modest-sized savings account, but in practice it can be a full-time job—one with strange hours and virtually no compensation. Tucker, who has discovered 234 large and small asteroids since 1996, shuts off his alarm clock at 4:15 in the morning, rolls out of bed, and goes outside to put covers on the mirrors of his three 14-inch telescopes. The $12,000 scopes take high-resolution snapshots of one particular strip of sky all night, but their efficacy declines rapidly as dawn creeps over the horizon. By 5:00, Tucker is already in front of his computer, scrutinizing the several hundred digital images his telescopes have just produced for signs an asteroid might be passing through. “I look for streaks,” he says. “Asteroids tend to move very fast relative to everything else.”

Software on Tucker’s computer compares his fresh images with maps of known stars and asteroids. This makes it easier for him to pinpoint potential new objects, but it still takes him about two hours to eyeball each morning’s photos. The drudgery is punctuated by occasional moments of excitement. “When I think I see something new, I go to the Minor Planet Center’s Web site and enter in the object’s coordinates,” he says. “If the site tells me ‘No known object,’ that’s when I start getting excited.” Once researchers at the MPC independently confirm his find, he can celebrate—and add another notch to his asteroid belt. It takes observations on at least three different nights to calculate an approximate orbit, but to really nail down an orbit so that the asteroid’s position can be predicted accurately for years in advance requires dozens of observations conducted over several years.

Although large, professionally conducted surveys like the Catalina Sky Survey, which uses telescopes in Arizona and Australia, and LINEAR in Socorro, New Mexico, have made the majority of Spaceguard finds, amateurs fill a critical role. “The surveys are sweeping the sky in a very systematic way, but amateurs can look outside of the survey paths, and they also have the flexibility to look closely at small patches of sky,” Chesley says. The Minor Planet Center at the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, which vets every reported asteroid discovery in the world, welcomes amateur finds. Any observatory, private or public, that passes the MPC’s initial test—recording telescope images of well-known asteroids and measuring their positions correctly—is assigned a site code (Dyvig’s is 918). Nearly a thousand amateurs have these codes, which enable them to submit discoveries for official verification. The amateur record holder is a Japanese engineering professor, Takao Kobayashi, who has a staggering 2,392 numbered asteroids to his credit.

While several members of Congress, including Rohrabacher, contend that a national prize program would help encourage the best amateur asteroid hunters, enthusiasts like Dyvig and Tucker don’t need a financial incentive. Their night job is its own reward. “Finding an asteroid or comet is an incredible experience,” Tucker says. “Imagine all the endorphins in your brain being released at once!” Chesley agrees: “The publicity that would go along with a prize might energize the amateur community and keep it more vibrant, but these people aren’t motivated by money.” All the same, Rohrabacher thinks awards would draw more Americans to the task of asteroid finding. He cites the success of the $10 million Ansari X-Prize, which reinvigorated the personal spaceflight industry and inspired the first private rocket ship into space. “Prizes are a great way of bringing about change,” he says. “They create competition, and there’s no cost unless someone succeeds.”

If an amateur or survey telescope did spot a potentially dangerous asteroid, there would be no need to build bunkers or mount Armageddon-style rescue missions right away. With only a few observations to feed into their calculations, the early estimates by scientists of an asteroid’s future orbit have huge uncertainties. Later observations that refine the predicted trajectory of worrisome rocks have always—at least so far—shown there’s no cause for alarm. For example, the asteroid Apophis, which initially seemed headed our way in 2029, now seems destined to miss Earth by thousands of miles, but there is still a 1-in-45,000 chance of an impact on April 13, 2036. “You can’t just discover something and say, ‘Oh, it’s going to hit us in 30 years,’” Chesley says. On the other hand, if an asteroid hit ever does appear to be in the cards, we will probably need many years to deflect it off course. The sooner we try to deflect an asteroid (perhaps by using the gravitational pull of a spacecraft to yank it onto a new course) the easier it will be, which is why Spaceguard is trying to catalog everything big enough to be a threat.

Regardless of how crucial Spaceguard’s mission turns out to be, the same march of technology that has made amateurs like Dyvig and Tucker so valuable to the asteroid hunt may soon make them obsolete. Instruments like the 8.4-meter Large Synoptic Survey Telescope, slated to begin operation in 2014, will use massive computer power to carry out continuous scans of sky for near-Earth objects, leaving ever fewer patches for amateurs to focus on. But Tucker isn’t deterred. His fellow amateurs, he points out, are starting to make an impact in other areas, like monitoring the fluctuations of variable stars and investigating powerful cosmic explosions known as gamma-ray bursts: “Something else is going to come along—and we’ll be able to contribute.”