Interplanetary fireworks show on July 4

The Deep Impact spacecraft will attempt to nail a passing comet, Tempel 1, with an 820-pound "bullet". If it's successful, the firework display should be visible with the naked eye and scientists hope to reap some detailed information about the composition of comets:

Scientists hope the July 4 collision will gouge a crater in the comet's surface large enough to reveal its pristine core and perhaps yield cosmic clues to the origin of the solar system.

NASA's fleet of space-based observatories — including the Hubble, Spitzer and Chandra telescopes — along with an army of ground-based telescopes around the world are expected to record the impact and resulting crater.

The big question is: What kind of fireworks can sky-gazers expect to see from Earth?

Scientists do not know yet. But if the probe hits the bull's-eye, the impact could temporarily light up the comet as much as 40 times brighter than normal, possibly making it visible to the naked eye in parts of the Western Hemisphere.

"We're getting closer by the minute," Andrew Dantzler, the director of NASA's solar system division, said earlier this month. "I'm looking forward to a great encounter on the Fourth of July."