I remember that question being asked on several shows. There are certain events that the whole nation, or most of it, understands. A shared consciousness.

January 28, 1986 - 73 seconds after launch, the space shuttle challenger exploded. I was in high school, and I can remember the social studies teacher wheeling out the television after the accident occurred. School stopped that day, and we were all glued to the televisions. There was a hushed silence in the school that day, for several minutes.
Those 73 seconds were played on the news that night, that day, that week. We heard a lot about space exploration after that. Really, NASA, which had been in the background for a few years, took center stage again. We heard about all seven astronauts that day, especially Christa McAuliffe – who was supposed to be the first teacher in space. The same Christa McAuliffe, when asked about the dangers of the mission, said, "Every shuttle mission's been successful."
Those older than me will remember Sputnik, they will remember Apollo 11 (Neil Armstrong, 'Buzz' Aldrin and Michael Collins) and Neil Armstrong's moon walk. Sort of reminds me of something Alan Shepard once said: "It's a very sobering feeling to be up in space and realize that one's safety factor was determined by the lowest bidder on a government contract."
The Day After
I was in middle school in 1983, when it seemed everybody watched "The Day After." Okay, I don't remember much about the movie, but it was a much anticipated movie, showing the effects of world war involving nuclear weapons. It was not the movie that was so important – but our reactions to the movie. This was in an age where newspapers had things about SALT and SALT II (Jimmy Carter), and Star Wars (Ronald Reagan). I was a child, so I did not pay close attention to it all. All I knew was that we had nuclear weapons, the USSR did as well, and we did not know if anyone could survive a "nuclear winter." This movie popularized the concept of a nuclear winter.
9-11
I remember hearing the news – about one, perhaps two airplanes that accidentally ran into a building in New York. Preliminary reports were very sketchy, and then when all flights were being grounded, we knew this was not an accident. I remember when there were 8 unaccounted for planes, one eventually running into the ground in rural Pennsylvania. And when we remember 9-11, most don't even recall the plane that hit the Pentagon. Sort of like it hit a military site, not as shocking as hitting a civilian structure. I did not really get that, but whatever.
Point is that this generation remembers what they were doing, whether it was getting breakfast, on the way into work, or waking up to a phone call from a friend or family member.
The point, I guess, is that there are certain events that grip the United States. Where we remember what we were doing when we heard. It is part of the American Consciousness.