1. On September 20, 2001, New York City Mayor Rudy Giuliani declared a day of mourning for the victims of the 9/11 terrorist attacks, which had occurred just nine days prior. The city observed three minutes of silence at 8:46am, the exact moment the first plane struck the World Trade Center.

2. On September 20, 1913, the New York Philharmonic made its first appearance at Carnegie Hall, which had opened the previous year. The concert featured works by Beethoven, Wagner, and Dvorak, and was conducted by Gustav Mahler.

3. On September 20, 1957, nine black students were blocked from entering Central High School in Little Rock, Arkansas, by the National Guard. The incident, which occurred in the midst of the civil rights movement, sparked widespread outrage and eventually led to the desegregation of public schools in the United States.

4. On September 20, 1973, singer-songwriter Jim Croce and five others died in a plane crash near Natchitoches, Louisiana, while on tour. Croce, whose hits included "Bad, Bad Leroy Brown" and "Time in a Bottle," was just 30 years old.

5. On September 20, 1966, the Metropolitan Opera House at Lincoln Center opened its doors for the first time. The opening night performance featured the world premiere of Samuel Barber's opera "Antony and Cleopatra," with Leontyne Price and Justino Diaz in the title roles.