 The relativity of simultaneity is a consequence of two startling assumptions. First, each of these “observers”, no matter at what (subluminal) speed or in which direction they or the source of the light are moving (as long as neither the speed nor the directions change), must come to the same result (conventionally indicated as \(c)\) when they measure the speed of light. We will not attempt to justify the assumption of the constancy of the speed of light here, though many standard texts present the empirical and theoretical background that led to it. Nor is it obvious that this assumption leads to the relativity of simultaneity, though one of the joys of even elementary presentations of the subject is that this prima facie astonishing connection can be convincingly demonstrated to persistent non-specialists.