This is a
question that some people (when I used to read alt.society.generation-x) used as a
marker for belonging to
Generation X; if you were too young to remember the explosion, then you were a
Millenial. It was an equivalent to the
Baby Boomers' "Where were you when you heard
John F. Kennedy had been
assassinated?"
Me, I was home sick from seventh grade, watching MTV in my bedroom; my mom came in from the living room to tell me what had been announced on the station she was watching. I remember MTV stopped using their "moon landing" station identification for a while, feeling that any reference to astronauts was inappropriate at the time.