Moments of silence. polo sandoval has more on that commemoration. >> reporter: good morning to you. 9/11 families once again are coming together here where the twin towers once stood. loaning on each other as they lead the country and the world in marking 21 years since that awful day. today includes six moments of silence. they will acknowledge the moment that the two hijacked planes hit each tower at the world trade center, when they fell and when they crashed into the p&g and the field in shanksville, pennsylvania, and the names will echo through downtown manhattan and will be several dig t...