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NEW YORK — On the 20th anniversary of the Sept. 11 terror attacks, six moments of silence are part of the memorial ceremony.

The public is invited to observe any or all of them.

Here is the list:

  • 8:46 a.m. ET: Hijackers crash Flight 11 into the north tower.
  • 9:03 a.m.: Hijackers crash United Airlines Flight 175 into the south tower.
  • 9:37 a.m.: Hijackers crash American Airlines Flight 77 into the Pentagon.
  • 9:59 a.m.: The south tower collapses.
  • 10:03 a.m.: Passengers launch a counterattack on hijackers aboard United Airlines Flight 93. The hijackers crash the plane into an empty field near Shanksville, Pa.
  • 10:28 a.m.: The north tower collapses.
  • Photos: 6 moments of silence to remember 9/11
    8:45 a.m. – Flight 11 struck the North Tower
  • Photos: 6 moments of silence to remember 9/11
    9:03 a.m. – Flight 175 struck the South Tower
  • Photos: 6 moments of silence to remember 9/11
    9:37 a.m. – Flight 77 crashed into the Pentagon
  • Photos: 6 moments of silence to remember 9/11
    9:59 a.m. – The South Tower collapsed
  • Photos: 6 moments of silence to remember 9/11
    10:03 a.m. – Flight 93 crashed in Shanksville, Pennsylvania
  • Photos: 6 moments of silence to remember 9/11
    10:28 a.m. – The North Tower collapsed