Watching the sound

There have been a lot of military planes training in the valleys this week. Several came thundering down the corridor over Keswick and over Bassenthwaite Lake. Their distance away was far enough to be able to tell that light travels much faster than sound. When the first one came through, I was looking at the sound and didn't see the plane. I saw the following plane and as it came past (circled in the picture) I started to count. I got to 5 seconds before the sound was directly in front of me. Sound travels at 330 metres per second so the plane was just over a mile away.