A big bang - and the small fry who'll see it

As cosmic objects go, Tempel 1 is something only an astronomer could love - a pockmarked potato half the size of Manhattan spewing dust and gas.

Nevertheless, the comet is getting star treatment of late from hundreds of people across six continents who have been tracking its movements with telescopes and feeding images of the comet to professional astronomers. The reason? On July 4, an American spacecraft will launch a projectile to slam into the comet and offer clues to what Tempel 1 is made of.

Whatever secrets it uncovers, the mission - dubbed Deep Impact - also highlights the key role amateur scientists play in several aspects of astronomy. Unlike the world of, say, biology or physics, the cosmos remains one of the few realms of science where dedicated amateurs can still make consistent, significant contributions. They feed professional scientists with data that track changes in variable stars. They discover and track comets and asteroids, hunt for planets beyond the solar system, and record changes in the afterglow of powerful gamma-ray bursts.

And while the glory associated with Deep Impact will go to the National Aeronautics and Space Administration and the scientists who conceived the mission and will record the July 4 collision with mighty mountaintop telescopes, some credit should be given to the amateur astronomers doing reconnaissance work.

"Observations from the amateurs ... have proved very useful," says Tony Farnham, a University of Maryland astronomer. The key is telescope time.

Dr. Farnham has been observing the comet once a month since January from the Kitt Peak Observatory near Tucson, Ariz. That's generous for professionals, who must vie for hours at major observatories. But "ideally, we would like to get images more frequently" in order to track changes in the comet's output of dust and gas, any sudden emergence of jets of gas, or changes in the form and structure of the comet's features, he adds.

The data amateurs provide help fill those gaps. And they aid in planning his next mountaintop observing run. The images are not as detailed as those from the telescope he uses. Still, "there are some very talented observers out there, and they have been getting some very high-quality images."

At least 250 amateur and professional astronomers are participating in the small-telescope science program. Sixty-nine are individuals operating from small observatories and backyard sites. Others are working in teams averaging at least four members apiece.

Their telescopes host light-gathering optics that range in size from 6 to 36 inches across. Some are commercially made, some are homemade, and none of the setups comes cheap. The participants must replace their eyepieces with digital imaging equipment sophisticated enough to meet the Deep Impact team's specifications. That can run into several thousand dollars.

Amateur groups got tapped in a roundabout manner, says Gary Emerson, an engineer and amateur astronomer who works for Ball Aerospace & Technologies Corp. in Golden, Colo., which built the Deep Impact spacecraft.

The impact may kick up enough dust to brighten the comet from a telescope-only object to one visible to the naked eye under dark skies or via binoculars under less favorable conditions. So the mission's public-outreach coordinator initially came to Mr. Emerson and asked about opportunities to involve amateur astronomers in visiting schools to give talks or hosting comet-collision parties during which the public could view the comet through amateurs' telescopes. Indeed, the mission has a component - the amateur observers' program - that follows through on that idea.

"But I said: 'There's a lot of really advanced amateurs around the world who would love to get involved in some serious science,' " Emerson recalls. He says he'll be recording the event from a new backyard observatory at his retirement spot in southwestern New Mexico.

When the comet slams into the spacecraft's impactor at some 23,000 miles an hour - an event one astronomer has likened to a 767 colliding with a mosquito - no one knows what the outcome will be. The projectile could ding the comet's ice-and-rock surface, excavating a crater the size of a house. Or it could carve a hole as wide as a football stadium and 14 stories deep. The Deep Impact spacecraft will observe the proceedings - fleetingly - as it speeds past the comet, then beam the results back to Earth for the first close-up of the anatomy of a comet.

But long after the big telescopes have turned elsewhere, the cadre of amateurs will still be staring at the afterglow of the celestial fireworks of the Fourth of July.