When you look to the horizon and see a contrail coming "towards" your location and then this airplane passes over your position and then goes off towards the other horizon (think flying north to south, or east to west) how much distance has this plane traveled when its contrail ceases to look like it is descending out of the sky and appears to just stop moving away from you? I know that the plane could be timed and that the speed could be plugged in to an equation of speed/time and figure the distance that way... Is there another way of figuring this out? Everytime I look up at work (outside, building a power plant) and see a plane flying over I wonder at how to go about figuring a solution to this question.