Observing a contrail
I once observed a contrail of a 747 using an astronomical telescope. The four lines from the engines were quite distinct. It appeared that they were moving backwards as fast as the 74 was moving forwards and eventually curled over each other, presumably in the vortex. They were still moving aft minutes later.
Speaking of vortexes, on a very rare day in Wellington NZ,s harbour I was completely becalmed off the end of runway 16 in my small yacht. I lay back in the sun waiting for a breeze when a QF SP flew over and landed. A few seconds later, hearing an odd noise, I looked up in time to see two dark pointed marks of turbulence racing across the water straight at me. I just had time to hang on before we were blasted over on our ear with me gazing at the keel. A few seconds of lashing thrashing drama before we rolled upright and everything returned to normal.
A perfect demonstration of vortex.