9/11: The moment before the second plane hits the World Trade Center

To me, this is the definitive image of 9/11.

United Airlines Flight 175, a Boeing 767-222, was hijacked by 5 al-Qaeda terrorists 30 minutes into its flight, and then crashed it into the South Tower of the World Trade Center, New York City, killing all 60 people aboard plus the hijackers.

Time of impact: 9.03am, which was 17 minutes after the first plane, an American Airlines Flight 11, crashed into the North Tower.

Due to TV cameras being trained on the WTC at that moment, the impact was seen live by a worldwide audience.

The South Tower collapsed 56 minutes after the crash.