By LEE BOWMAN
Scripps Howard News Service
July 01, 2005
The Deep Impact mission involves a probe that's been closing with the comet for months, releasing an 816-pound projectile into the comet's path, then moving away to a safe distance to record the result with cameras and other instruments 24 hours later.
The idea is to create a fairly large crater and reveal formations underneath the surface. The flyby spacecraft will have just over 13 minutes to gather data until it will no longer be in position to see the impact site, said Karen Meech, an astronomer at the University of Hawaii who is helping coordinate ground-based observations.
Several other spacecraft, including the Hubble Space Telescope and the Chandra X-ray observatory, and at least 60 large telescopes in 20 countries, will also be watching the event long after the collision. "Ground and Earth-orbital observations will be key to realizing the full scientific potential of the mission."
The collision is slated to happen at 1:52 a.m. EDT Monday (10:52 p.m. PDT Sunday), after the comet will have slipped below the horizon in the eastern half of the United States and Canada, but should be visible in any clear, dark sky in Western states.
Keep in mind, the encounter is taking place 83 million miles away, so there will be about a 10-second delay in seeing any flash from Earth.
"Anyone west of the Mississippi River has a chance of seeing the comet when Deep Impact slams into it," said Kelly Beatty, executive editor of Sky and Telescope magazine. "People in southwestern Canada, Mexico and Central America will have good seats, too."
Here are some hints on how to find Tempel 1. After dark, locate Jupiter shining high in the southwest. It's the brightest object in that part of the sky (Venus sets to the west-northwest at dusk).
Once you find Jupiter, look off to the left, a bit more than the width of a fist seen at arm's length, and find the somewhat fainter star Spica. The comet will be a couple of finger-widths above Spica on impact night, and gradually move farther to the upper left of the star during the rest of July. The comet is near its closest approach to the sun, and the tail should be streaming back away from Jupiter.
For Easterners, the hope is that while they may not witness the historic bump, the cloud of dust and rocks will linger around or behind Tempel 1 for several nights, perhaps for weeks.
For those who aren't able to see for themselves, many of the observations from professional observers will be posted on a mission Web site. Well-equipped amateur astronomers (those with an 8-inch-or-larger telescope and a high-quality digital camera) who do get a good look are being asked to submit observations to a related site.
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