Today was a beautiful clear day here in South Western PA. While I was busy cleaning up the yard and burning scrap wood and limbs, I took my binoculars with me and watched the planes fly over. It is fun to do that wondering where they are coming from and where they are going. Fall and Winter are always the clearest days to watch planes here. Fun thing to do when you are outside working. One thing to ask though, What causes some planes to leave a vapor trail behind and some not to. I always thought it had something to do with higher altitude and the air temperature.