Astronomy buff Barry Peckham said that while the mission is exciting, folks on the ground aren't likely to be impressed by the visuals.

"It's 100 percent mind candy — the idea that we're going to be able to hit something that far away. It's a technological, gear-head accomplishment and I'll be impressed if they do it. But you won't be able to see it," he said.

The event, after all, will be 83 million miles away, and it won't be completely dark here at impact time. Furthermore, in urban parts of the Islands, light pollution will make it still harder to pick anything out.

But it's still worth looking, said Karen Meech, co-investigator on the Deep Impact science team and an astronomer with the University of Hawai'i Institute for Astronomy.

"I've been telling people all along it's possible that it will reach naked-eye visibility, but it won't be spectacular. Still, I think some people will be interested in actually seeing it live," Meech said.

She said the latest imagery from the comet suggests there is reason to hope for a big dust cloud that may make Tempel 1 glow like a star, as viewed from Earth.

"We're seeing outbursts from the surface, like explosions. Nobody has predicted that and we've never seen that before from a comet," she said.

It suggests that the surface may be comparatively soft, and she hopes it means the impact of the probe may throw up a huge cloud of dust and ice.

"People shouldn't expect to go out and see something" before the impact, said Bishop Museum planetarium manager Carolyn Kaichi. But it's possible, with clear skies and a pair of binoculars, that if you're watching the location just northeast of Spica, a blue-white star to the southwest of Jupiter, you'll suddenly see a light, like a star blinking on, she said.

Meech said a good backyard telescope in a good viewing location can pick out the comet, but Institute for Astronomy educator Gary Kajihara agreed that Tempel 1 is difficult even for experienced amateur astronomers to find.

"We don't want to promise anything, but you may see a new 'star' appear around the region of Spica," he said.

What, if anything, will be visible to folks on the ground depends a great deal on where the probe hits and what the comet is made of — how hard it is, and how much dust and ice gets blasted off.

"It's not really known how solid it is. That's one of the things we'll know more about after this experiment," said Bob McLaren, deputy director of the Institute for Astronomy. One of the main goals of the experiment is to study the exploded cloud of dust and ice to determine the makeup of the inside of a comet.