The South Tower of the World Trade Center explodes in flames after being hit by the hijacked airliner now universally known as "the second plane," United Airlines Flight 175, September 11, 2001. This photo -- with its black smoke; the shocking, brilliant, colossal flames; the cloudless sky; the beautiful Brooklyn Bridge flying the American flag -- captures so much of the story of the day that, if one were to create a composite picture to illustrate the idea of "9/11," the result might look very much like this astonishing shot.
(Photo: STR/Reuters /Landov)