Relatives of victims killed at the World Trade Center are observing a moment of silence to mark the seventh anniversary of the Sept. 11 terrorist attacks.
The silence marks the exact time — 8:46 — when the first hijacked plane struck the trade center. Other moments of silence were 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 Thursday, Barack Obama and John McCain are due at ground zero to pay silent respects.