I know this is OT - but I'll quickly add that they have a mobile app that even has a "augmented reality" feature where you can point your phone camera around and it'll show you the flights on your screen that are visible in your line-of-sight. You won't see military flights on there for the most part, but commercial, Project Loon balloons, and recreational aircraft all show up. It's been helpful when I hear a helicopter fly low over and I'm trying to figure out who it is.
If nothing else, goes to show you that even when air travel is "slow" there's still a crap ton of planes flying around up there.