What causes the observable time delay between seeing a rocket ignition flash and hearing its roar?

The sound of the powerful rocket launch travels at the speed of sound, which is significantly slower than the speed of light.

The sensory discrepancy experienced during a close-range rocket launch—seeing the bright ignition flash instantly followed by a delayed auditory experience—is a direct consequence of fundamental physics regarding wave propagation speeds. Light travels nearly instantaneously across typical viewing distances, meaning the visual cue of ignition is perceived immediately. However, sound travels much slower, at the speed of sound. This speed differential ensures that the deep, chest-rattling roar arrives seconds later, after the sound wave has physically traveled the distance between the launch site and the observer. This delay is a tangible metric that can actually be used to estimate one's physical distance from the launch pad.