actually, you can't do much better than einstein's description.
imagine you are on bike (or tram car in vienna!) you're traveling in a straight line.
the bike keeps going faster--so fast, it beings to appoach the speed of light! You are carried along with the bike..
how do you know that the speed is close to the speed of light? well, you begin to notice thing coming towards you are getting redder.. red being a highest frequence of light humans can see, and if you looked behind you, things would be bluer! (you are moving so fast, you can only see the leading edge of white light!)
just like the forward motion of the train, that "pushes" the sound ahead of it, (making it seem a higher pitch) and that adds its own speed to the speed of sound (making the whistle behind it sound lower) your movement pushes you into the red!
doppler effects show up all over, your hard drive has software to counter the dopple effect that it experiences!
