The comets are coming!

A second "home" for comets is the Kuiper belt. It's named for another Dutch astronomer (what is it with the Dutch and comets?), who deduced its existence. It lies like a flattened doughnut at a distance of from 30 to 50 AU. Here, at least 100 million objects larger than .6 mile in diameter are thought to orbit the sun. Halley's comet, one of the most famous, originates here.

These close-in comets, which orbit the sun once every 200 years or less, include Stardust's target: Comet Wild 2. During the craft's comet encounter in January, it snapped some great photos of Wild 2's nucleus. "The images are quite spectacular," says Thomas Duxbury, the mission's project manager at Cal Tech's Jet Propulsion Laboratory in Pasadena, Calif. (We've reproduced one of them above.)

The nucleus, he says, looks like a hamburger patty with a bite or two taken out of it. It's a big oblong burger - measuring about 3.4 miles long, about 2.5 miles wide, and 1.9 miles thick. The comet overtook Stardust from behind, coming to within about 148 miles of it.

It was a wild ride. Dust particles and spacecraft collided at bulletlike speeds. Stardust gave its earthbound handlers a few tense moments during its closest encounter, which lasted tens of minutes.

The spacecraft is shielded with three layers of material, each acting like a bullet-proof vest. Each layer has its own dust counter so engineers can see how well the shields are performing. Roughly a dozen particles about an inch across punched through to the second shield. The systems that help keep the craft stable and the shields pointed toward the oncoming stream of dust worked extra hard to keep the craft from becoming a tumbling hunk of hardware.

"We did hold our breath a little bit," Mr. Duxbury says. But once the craft had passed safely through the coma - the halo of dust and gas around the nucleus - "of course we told everybody we knew it would work all the time."

Special gel-filled collectors swept up some of the comet dust while the spacecraft's camera snapped away. Where movies like "Armageddon" (1998) show a nucleus with jets of gas erupting all over the place, Stardust found only a couple of dozen. Even that was a surprise, since the team only expected one or two. As the sun heats the nucleus, subsurface ice and frozen gases vaporize, spewing through the surface. The gas and dust form the coma and tail. Wild 2's surface was remarkable, Duxbury says. "We were seeing bedrock - the actual solid surface."

They also saw stair-step formations on the surface, as well as spires that appear to be from jets of dust and gas that long since have shut down.

If Comet Churyumov-Gerasimenko, Rosetta's target, is like Wild 2, the European probe should have no trouble finding a landing spot.

If you want to watch this spring's cometary extravaganza, grab a pair of binoculars. Binoculars will help you see the comets if they don't get bright enough to spot with the naked eye.

Try to find an observing spot with a low horizon. If that's your backyard, great! Otherwise, look for a nearby hilltop or a big park where the treetops appear low in the distance.

Set your alarm clock to see LINEAR. In early May, that comet should appear about an hour before sunrise just above the eastern horizon. If you miss it, don't despair: LINEAR will reappear in the southwestern sky at twilight in late May (as shown on the chart above).

You can watch comet NEAT in the evenings, starting around May 5 or 6. It should appear at the end of twilight, just to the left of Sirius, the "dog star."

Use the sky charts above to find out where to look for the comets on a given date. (Charts are also available at: skyandtelescope.com/observing/objects/ comets/article_1229_1.asp.)

Scan the indicated part of the sky slowly to spot the comet. If the comet appears faint, shift your eyeballs (not your binoculars!) slightly to one side. This should give you a brighter view.

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