(September 11, 2003) - (Undated-AP) -- Memorials are being conducted across Arkansas and throughout the nation to mark the second anniversary of the September eleventh terror attacks. A ceremony at ground zero in New York is to last three and one half hours, with moments of silence at four different points -- the time of impact of each plane that flew into the trade center, and the time of each tower's collapse. In Washington, President Bush planned to observe 7:46 a.m. Central time, the moment when American Airlines Flight 11 struck the trade center's north tower to begin the timed attacks. A ceremony at the Pentagon was to include a moment of silence at 8:37 a.m. Central time, when the impact of a jetliner killed 184 people. And in southwest Pennsylvania, rural hamlets were to toll bells to mark the time when the fourth hijacked plane plunged into a field there -- 9:06 a.m. Central time. Forty passengers and crew were killed. People on the flight were later hailed as heroes for trying to stop more catastrophe.