"It appears to be a dot of light in the sky, moving ... like a plane going over, but silent and without flashing," said Jonathan McDowell of Jonathan's Space Report and Harvard Center for Astrophysics. It can be viewed in the early evening when it's dark and the satellite is high enough in the sky that its metal is reflecting sunlight. Until the weekend, the satellite - called USA 193 - is supposed to pass over some U.S., Canadian and western European cities, moving generally from southwest to northeast. McDowell suggests times and locations might be found at http://www.heavens-above.com., though the site has been overwhelmed in recent days.

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THE SHOOTDOWN

Chances of seeing the missile launch are slim "unless you're underneath it on the ship in the middle of the Pacific Ocean," said Riki Ellison, president of the Missile Defense Advocacy Alliance, who has been on ships to witness past missile defense tests.

The military wants to attempt the shootdown during the day. There is some chance those in western Hawaii "might be lucky and see the streak of the missile going up in the sky in the distance," said McDowell, adding it will be very difficult to see against the daytime sky.

Ditto for the flash from the collision, if a missile actually hits its mark.

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THE DEBRIS

If the satellite is pulverized into tiny pieces, it won't leave much to see. Chances are a little better if big chunks remain that "could stay in orbit for a couple of weeks," McDowell said.

"Overall, the average person won't be able to see much of anything," he said.

Ted Molczan, a hobbyist satellite observer who has tracked USA 193 since its launch in December 2006, is slightly more optimistic. Fifteen hours after the intercept, depending on cloud cover, observers near latitude 50 degrees north will be able to scan the satellite's known orbit to determine whether it is still there.

"They could also detect debris in orbit," he said. But, he added, "There is a lot of cloud at mid-northern latitude during the winter."