LCROSS (Lunar CRater Observation and Sensing Satellite) is about to hit the moon. The exact time of the impact (give or take a few seconds) is Friday 9th Oct 2009 11:31:30 UTC (about 7.30 EDT).
Its going to hit at about 9000km/hr (~2.5km/s), and with a mass of about 2 tons that will give it about the same energy as a ton of TNT. Its not quite the biggest extra-terrestrial manmade silent bangs ever. Deep Impact which hit comet Temple had a considerably smaller impactor (~400kg) but went MUCH faster (MV^2 counts!). Deep Impact hit the comet at about 10 km/s and had the same energy as about 5 tons of TNT