I remember sitting at my desk at work that morning in 2001 watching what was going on in New York.  The City’s cable access channel staff had their TV feeds going all day long.

I also remember how quiet it was in the sky when I got home that evening.  That day the FAA closed all airspace and grounded all flights.

It went from this (9:30am EDT):

to this (after 12pm EDT):

It was very quiet over the skies in SoCal on the 12th.  Flights resumed on the 13th and 14th in tiers.  By the 21st they were fully restored.  Watch the video here.  For more info on 9/11, click here.