When a rocket passes by, you might notice a delay between the time you see it and the time you hear the sound it produces. This phenomenon is known as the "sonic boom" and occurs due to the way sound waves propagate through the air.
The speed of sound is finite, and it travels at approximately 343 meters per second (at sea level and room temperature). When an object moves faster than the speed of sound, it creates a shock wave, which manifests as a loud boom. This shock wave is the sonic boom.
When a rocket is approaching you, the sound waves it generates move toward you at the speed of sound, so you hear the sound almost instantly. However, as the rocket moves away from you, it outpaces the sound it produces. This means that the sound waves take time to catch up with the rocket and reach your ears, causing a delay between the visual sighting of the rocket and the arrival of the sound.
The sound of a rocket passing by typically consists of multiple components. Initially, there might be a low rumbling sound as the rocket's engines become audible. As it gets closer, you hear the roar of the engines at their maximum intensity. After the rocket has passed, you may still hear a fading rumble as the sound waves continue to reach your location.
It's worth noting that the distance between you and the rocket, the rocket's speed, and atmospheric conditions can affect the intensity and duration of the sound you hear. Additionally, the specific design of the rocket and its engines can also influence the characteristics of the sound produced.