Seven years ago today, America and the world was changed forever. The U.S. marks the day with solemn rituals and the opening of a memorial at the Pentagon.
Relatives of victims killed at the World Trade Center are observing several moments of silence. The first marks the exact time — 8:46 — when the first hijacked plane struck the trade center. Other moments of silence are planned for the times when the second plane hit and when the towers fell.
Other ceremonies are being held throughout the day, including one at the Pentagon, where a new memorial will be dedicated. Services will also be held in Shanksville, Pa., where one of the hijacked planes crashed.
Later today, Barack Obama and John McCain are due at ground zero to pay silent respects.