When observing distant landmarks from aboard a moving train, it is noticed that those features that are closer to us seem to go past much faster than those that are further away. Indeed, very distant stationary objects traverse our field of view so slowly that they appear to be moving with the train. These otherwise fixed objects can thus appear to someone on the moving train as being in relative motion with one another. This apparent movement effect, caused by variations in proximity, is referred to as parallax.
The effect can be useful inasmuch as it allows for the determination of observer-object distances, as illustrated via Fig. 1, below.
