Bishop Museum is orchestrating a special event for the impact, with telescopes on the lawn and an informational program in its Planetarium.

"They don't expect it to be visible to the naked eye, but with binoculars, maybe" and certainly with a telescope, said Planetarium manager Carolyn Kaichi.

On the Big Island, the University of Hawai'i's Institute for Astronomy's Hilo headquarters is planning "a very big public outreach program" with astronomers, educational materials and video of the impact. The institute also is hoping to get near-real-time images of the comet from a large amateur telescope on Mauna Kea, said Gary Fujihara, science education and public outreach officer.

Technicians prepare the Deep Impact spacecraft for its mission — releasing a probe to smash into the comet Tempel I on July 3. The impact is expected to throw up a huge cloud of dust visible from Hawai'i, astronomers say. Peter Cosgrove • Associated Press

The impact should throw up a massive cone of dust and debris that should be visible from Earth. The timing is set so that it can be viewed from sites in California and Australia, and since Hawai'i falls in between, it is in a perfect viewing spot.

The dust cloud should be visible for hours, or perhaps as long as days, Kaichi said. NASA officials say it is possible that people viewing the right spot in the sky could see the flash of impact with the naked eye.

The dust and debris is the key to the mission.

Scientists have been able to fly spacecraft through the tails of comets, so they know what's blowing off the surface of these space travelers. But the Deep Impact mission is designed to find out what's inside comets: How much is water, how much is rock, how dense it is, whether it's layered, and much more.

"It is a big deal," Fujihara said.

"We will be capturing the whole thing on the most powerful camera to fly in deep space," said Michael A'Hearn, principal investigator on the Deep Impact mission and a University of Maryland astronomy professor.

By analyzing the images, researchers hope to learn about the structure at the heart of comets. Astronomers believe that comets may have frozen within them materials that are the building blocks of planets, and that they may also contain water, which is required for life as it is seen on Earth.

Scientists say they are certain the collision will not threaten us.

"In the world of science, this is the astronomical equivalent of a 767 airliner running into a mosquito. It simply will not appreciably modify the comet's orbital path. Comet Tempel I poses no threat to the Earth now or in the foreseeable future," said Don Yeomans, a Deep Impact mission scientist at California's Jet Propulsion Laboratory, which manages the project for NASA.