In early July, NASA’s Deep Impact spacecraft will deploy a tiny impactor to smash into the nucleus of a small comet. The idea is to excavate a sizable crater and provide valuable insight into the true nature of comets.
For skywatchers here on Earth, it should also produce a large cloud of ejected material that should cause the comet to significantly brighten enough to become visible with binoculars and perhaps even with the unaided eye.
The comet that has been chosen for the task was discovered by a Frenchman in the mid-19th century. Known as Comet Tempel 1, it already has a rather checkered history. Soon, however, it will go down in history books.
Finding the target
During June, Comet Tempel 1 will be gliding on a south-southeast course through the constellation of Virgo, the Virgin. The comet will have already made its closest approach to the Earth in early May at a distance of 66 million miles (106 million kilometers)...cont'd
http://www.space.com/spacewatch/050603_deep_impact.html