Star Points for July, 2005; by Curtis Roelle Space Probe and Comet to Go Bump in the Night If all goes according to plan an obscure comet could brighten to naked eye visibility on Independence Day due to man made effects. An "impactor" module aboard the Deep Impact mission will be slammed into Comet Tempel 1. The impact should excavate a crater on the comet's surface and sunlight hitting the resulting debris cloud is expected to cause a temporary brightening of the comet. Deep Impact began its journey when launched from Florida last January. The spacecraft consists of two components, an instrument assembly and the 820 pound impactor. Photographs imaged by the instrument assembly will be used to guide the spacecraft on its final approach to the comet which is scheduled to release the impactor about 24 hours prior to impact with Tempel 1. The impactor is constructed primarily of a solid copper mass which is predicted to slam into the comet at a velocity of 23,000 mph. Technically speaking, like a possum on a Carroll County highway at night, the impactor will scurry in front of, and get run over by, the comet. The impactor is equipped with "smart" technology allowing it to perform last minute navigation using its own imager and propulsion system. The impact is to occur around 2 a.m. on the morning of Monday, July 4. Unfortunately, the comet will be below the horizon for observers in Maryland. The time was chosen so that the spacecraft can be observed simultaneously from tracking stations in both California and Australia. Our first opportunity to view any possible results of the impact will come later that night as twilight fades. The comet could reach naked eye visibility when viewed from a dark country site far away from city lights. Binoculars may also be a good way to track the comet and any changes that may occur. During the encounter the comet will appear in the sky in the constellation Virgo near the bright star Spica. See SkyandTelescope.com for up to date finder charts. Comet Tempel 1 was discovered from France by Earnst Wilhelm Liebrecht Tempel in 1867. Tempel 1 is a short period comet and orbits the sun every 5.68 years. Without accounting for any effects caused by the impact, normal predictions call for the comet to be only about magnitude 10 during the first week of July. At the time of impact the comet will be more than 80 million miles from the earth. At that distance the chances of any dangerous side effects are essentially nil. Deep Impact is one of NASA's "discovery" program missions. It is a partnership between the University of Maryland (UM), the California Institute of Technology's Jet Propulsion Laboratory (JPL), and Ball Aerospace. The Principal Investigator is Dr. Michael F. A'Hearn, head of the Astronomy Program at UM.