Do you remember that for a few days after 9/11 planes were not allowed to fly over the U.S.? I stood in my backyard in Denver a day or two after the attack and listened to the absence of airplanes. Everything was strange and raw in those first days but the quiet in the sky was eerie. It added to my sense that everyone was holding their breath.

I’m in the den in Albuquerque this morning. It isn’t so hot yet that we have to close up the house and turn on the air conditioning. I can hear through the open windows the normal sounds of our neighborhood. In the past 10 minutes or so I’ve heard birds, cars, sirens, dogs, wind chimes, children’s voices, and planes.

The next time you step outside, listen for planes. I imagine that in any urban area, and many not-so-urban areas, you will hear them. You may have to make an effort, though; not to hear them but to know that jets or props are what you are hearing. They are part of the background now. White noise.