# Explain this common observation clearly---If you look out of the window of a fast moving train

Explain this common observation clearly—If you look out of the window of a fast moving train the nearby trees, houses etc., seem to move rapidly in a direction opposite to the train’s motion, but the distant, objects (hill tops, the moon, the stars etc.,) seem to be stationary. (In fact, since you are aware that you are moving, these distant objects seem to move with you.)

A line joining the object to the eye is called the line of sight. The relative speed of any object outside the hist moving train (seems to be hist or slow) is decided by the angular speed of its line of sight. The line of sight of nearby object i.e. trees, houses etc., crosses large angles in a short interval of time and therefore, appears to run hist in opposite direction.The line of sight of very far away objects i.e. hill tops, the moon, the stars etc., crosses a very small angle in the same interval of time and hence appears to be stationary i.e.- moving in the direction of train.