Isn't there a flight tracking website somewhere that shows you the position of all US and perhaps transatlantic flights too?
All you'd need is the flight no.
Failing that if you can either judge the difference between mid level and high level traffic and make an assumption about height, therefore range, or use a bit of aircraft recognition, a table of wingspans and a telescope/bins with an angular graticule you could do the job scientifically. Then measure the angle of the aircraft from the vertical/horizon abd again simple trig gives you an answer.
All the same, it seems a lot of faff just for curiosity.