The first was held at 8:46 a.m. ET, to mark the moment that Al Qaeda terrorists crashed American Airlines Flight 11 into the north tower of New York’s World Trade Center two decades ago.

The second, 23 minutes later, will be at the same time that American Airlines Flight 175 hit the south tower and the third at 9:37 a.m. ET, allowed people to remember those who lost their lives when American Airlines Flight 77 crashed into the Pentagon.