the next method that is used is a method which again is familiar to people on the earth — surveyors use it all the time — and that's what we call triangulation, and the idea there is that if you look at a distant object against an even more distant background, then the apparent direction will depend on where you're standing, and if you move from one end to the other of a baseline, then a distant steeple, for example, will appear to move against the hills on the horizon.